Innovative Craft Beers Added with Purple Grape Pomace: Exploring Technological, Sensory, and Bioactive Characteristics

Abstract

Purple grape juice produces a significant amount of grape pomace (GP) as a by-product, which can be reused as a raw material in producing craft beers with bioactive properties. The objective of this study was to produce craft beers with the addition of GP during the fermentation process to evaluate the incorporation of bioactive compounds, aiming at using a by-product generated in the production of grape juice. Craft beer was produced, incorporating GP at concentrations of 1%, 5%, and 10% (w/w), and the physicochemical, technological, bioactive, and sensory properties were evaluated. The beers with the highest concentrations of GP (10% w/w) exhibited higher bioactive concentrations, including phenolic compounds (308 mg GAE/L), flavonoids (0.05 g of quercetin/L), anthocyanins (754.6 mg cyanidin-3-glucoside/L), and antioxidant capacities, as measured by DPPH (1878.2 µM Trolox/L), ABTS (4294.5 µM Trolox/L), and FRAP (844.7 mg ascorbic acid/L) methods. Adding GP promoted lower brightness (62.2) and intensified the a*, b*, and chroma parameters (18.0, 10.1, and 20.6, respectively), with the pigments of GP contributing to changes in the color parameters. However, increased sedimentation was observed under both conditions analyzed (4 °C and 25 °C), due to the higher presence of particulate matter from GP (3.4% and 3.7%, respectively). In general, for sensory analysis, while the knowledge of beneficial effects did not significantly change emotional responses, there were distinct emotional profiles associated with different beer samples. Utilizing GP for the bioactivation of beer is a positive approach to enhance its overall properties and an effective way to address issues related to the disposal of this by-product.

1. Introduction

The grape juice industry represents a traditional and well-established sector, playing a significant role in the economy and diversifying beverages for human consumption. The global grape juice market generated approximately USD 5 billion in 2023 and is projected to grow by 3.29% by 2028 [1]. The continuous and increasing demand for this product reflects a significant change in consumer behavior, with more people valuing beverages that combine convenience and nutritional quality. Additionally, consumers want to adopt healthier habits to improve their quality of life [2,3].

The consolidation of global information about the sector is quite irregular. However, countries such as the Netherlands, Chile, the United States, South Africa, Australia, Egypt, Brazil, Mexico, Turkey, and Greece lead in the production and export of grape juice [4]. In Brazil, for example, the per capita consumption of grape juice was estimated at 1.4 L in 2022, and the national production is estimated at approximately 190 million liters of grape juice per year [5,6]. Along with the growth in consumption and market expectations, there is a significant generation of by-products from the processing, particularly skins and seeds, which are produced from pressing grapes for juice extraction. The solid by-products represent approximately 20–25% of the material processed to produce around 1.5 billion liters of grape juice worldwide. This results in an enormous amount of solid material that remains underutilized globally [1,7].

Although grape pomace from juice production is often discarded without utilization, it still represents a diverse source of important nutritional, bioactive, and technological components. This is because only a small portion of the components are transferred from the grape to the juice during processing. In terms of composition (dry matter), grape pomace has high concentrations of proteins (~8.49%), lipids (~8.16%), carbohydrates (~29.2%), and phenolic compounds (60.1 mg of gallic acid equivalent/g) [7]. These components are associated with various biological activities, including antioxidant, antimicrobial, and anti-inflammatory properties [8]. Due to its composition, the solid by-product can be conveniently processed and utilized to prevent improper environmental disposal, leading to the proliferation of insects, urban pests, and unpleasant odors. Additionally, inadequate disposal can result in the excessive release of phytotoxic and antimicrobial components into the soil, impairing soil quality and viability [9,10].

Various strategies have been explored to mitigate the negative impacts of GP, including the extraction of bioactive compounds [11], transformations of GP into flour and food ingredients [12], and even its use as a raw material for the production of bioethanol [13]. However, no reports exist on using purple GP as an adjunct ingredient in producing bioactive craft beers by applying it directly to the beer wort during main fermentation. There is only one report of pasteurized (70 °C) and unpasteurized white GP in the second stage of beer fermentation [14]. Another report is about the application of red grape must and pomace that undergoes a process of saturation with gas (CO₂ and N₂), drying, and pressing, with subsequent application in the fermentation process for beer production [15]. One of the advantages would be the immediate use of fresh grape pomace, which preserves bioactive compounds, such as anthocyanins and phenolic compounds, that are sensitive to light, pH, and high temperatures, in addition to not requiring any auxiliary mechanism, such as drying or freezing [16].

Craft beers are produced through the alcoholic fermentation of malt derived from malted barley and potable water, with the addition of hops. During fermentation, yeast consumes fermentable sugars, producing ethanol and carbon dioxide [17,18]. Craft beers are generally characterized by smaller production volumes, various styles and flavor profiles, and less automated and more customized methods [19]. The bioactivation of beer can occur through mixing different components present in the raw materials used in beer production or by incorporating components that, in addition to their nutritional role, provide additional health benefits when consumed in low to moderate amounts. These benefits may include antioxidant properties, cardiovascular health support, prevention of osteoporosis, and protection against certain types of cancer [20,21].

The use of a solid by-product rich in bioactive compounds in the production of craft beers is an emerging field that aims to attract craft beer enthusiasts and health-conscious consumers and contribute to product personalization and diversification of styles and flavors offered by the beverage industry. In addition, this process helps to reuse valuable components, thereby contributing to a circular economy and adding economic value. Therefore, this study aimed to develop craft beers added with purple grape pomace and evaluate technological, bioactive, and sensory properties.

2. Materials and Methods

2.1. Materials

2,2-diphenyl-1-picrylhydrazyl (DPPH), 2,2-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS), potassium persulfate, 2,4,6-tris(2-piridil)-s-triazina (TPTZ), and 6-hydroxy-2,5,7,8-tetramethylchroman-2-carboxylic acid (Trolox) were purchased from Sigma-Aldrich^® (St. Louis, MO, USA). All other chemicals used were of analytical grade and were used as received without any further purification; they were obtained from Synth^® (Diadema, SP, Brazil) (ethanol 96%) and Isofar^®, (Rio de Janeiro, RJ, Brazil) (isooctane, sodium hydroxide, hydrochloric acid, sulfuric acid, and methanol). Purple grape pomace was obtained from a local purple grape juice producer in Rio de Janeiro, RJ. The fresh material was placed in airtight bags to preserve it and avoid any external contamination, being immediately stored at 4 °C and promptly used in beer production. The malt and hops used to produce Pilsner craft beer were purchased from the Brew Beer Shop company (São Paulo, SP, Brazil). The yeast Saccharomyces cerevisiae (Dry Ale Yeast—Safale US-05) was purchased from Fermentis (Marcq-en-Barœul, Lille, France).

2.2. Characterization of the by-Product; Craft Beer Production; and Physicochemical, Technological, and Sensory Properties

2.2.1. Proximal Composition of Grape Pomace

The proximal composition of the grape pomace was determined following the official methods for ash, lipid, moisture, and protein contents (calculated using the conversion factor 6.25) [22]. The carbohydrate content, including fiber, was calculated by subtracting lipid, protein, moisture, and ash from 100%. The energetic value was calculated based on the composition using Atwater conversion factors of 4, 9, and 4 kcal/g for protein, lipids, and carbohydrates, respectively [23].

2.2.2. Production of Craft Beer with Grape Pomace

The craft beer was produced following the traditional Pilsen Cream Ale production method, according to the guidelines provided by malt and hop suppliers and as described in the methodology by Piva et al. [24]. For this, 4.6 L of mineral water at 66 °C was added to 1.35 kg of malt (Pilsen malt, wheat malt, and cornflakes). The mixture was kept under constant stirring and temperature (66 °C) for 75 min for the saccharification of the wort starch. Afterward, the mixture was filtered, and the retained material was washed with 3.7 L of mineral water to extract the residual sugar from the malt bagasse. The filtered material (permeate) was then heated to 100 °C and maintained at that temperature for 60 min, with hops added at three stages (Chinook hops at 30 min, Whirlfloc at 50 min, and Chinook hops at 60 min). After heating, the wort was clarified (filtration) and cooled to 20 °C, followed by aeration of the wort through vigorous agitation during the cooling process. The cooled and aerated wort was divided into four bioreactors: (1) control without the addition of grape pomace; (2) addition of 1% grape pomace; (3) addition of 5% grape pomace; and (4) addition of 10% grape pomace. Fermentation was initiated by inoculating previously hydrated Saccharomyces cerevisiae yeast (0.5 g/L) and maintaining the temperature between 18 and 20 °C for 7 days. After the fermentation period, the temperature was lowered to 4–6 °C, where it remained for 10 days for maturation. The beers were bottled in 500 mL amber bottles, to which 0.5 g/L of sucrose was added (for secondary carbonation), followed by homogenization and sealing with a beer bottle cap. They were then kept at 20 °C for 10 days. After this period, the beers were used for subsequent analyses.

2.2.3. Physicochemical Characterization, Technological Properties, and Color Profile

The pH was determined using a digital pH meter. The total soluble solids (SS) and density values were determined using a digital refractometer. Titratable acidity (TA) was determined by titration with 0.1 M NaOH solution and 1% phenolphthalein as an indicator [22].

The determination of foam formation and stability (beer foam) in the beers was conducted using a method adapted from Leike [25] based on the deposition of the beers in a graduated cylinder. A quantity of 20 mL of beer at 4 °C was added to a fixed height of 19 cm from the bottom of a 2.5 cm diameter graduated glass cylinder at a 45° angle. After the complete addition of the beer, the cylinder was immediately returned to the standard angle, and the foam layer formed was measured (cm) and monitored for 5 min.

The alcohol content was determined by high-performance liquid chromatography (HPLC) with refractive index detection (RID), according to BallL and Lloyd [26]. The solvent flow rate was 0.8 mL/min, and an Agilent Hi-Plex H ion-exchange column (300 × 7.7 mm) with an 8 μm particle size was used, protected by a PL Hi-Plex H guard column (5 × 3 mm) (Agilent Technologies, Santa Clara, CA, USA). The separation temperature was set at 60 °C, with a run time of 20 min. The mobile phase consisted of 0.004 M H₂SO₄, and compound detection was achieved by comparison with external standards. The methodology was validated for linearity, recovery, and limits of detection and quantification [27].

The bitterness of the beers was determined following a protocol adapted from Analytica EBC (Section 9, Method 9.8—Bitterness of Beer IM) [28]. Thus, 2.5 mL of the de-carbonated sample was added to 0.25 mL of 3 M HCl and 5 mL of isooctane, and the mixture was agitated for 15 min at 30 rpm. The samples were then centrifuged for 3 min at 3000 rpm at a temperature of 4 °C. The bitterness units were determined using a spectrophotometer at 275 nm (the wavelength at which iso-α-acids, responsible for bitterness, absorb radiation), with isooctane used as a blank. The bitterness in IBU (International Bitterness Units) was calculated using Equation (1):

IBU = 50 × A

(1)

where IBU is the bitterness unit and A is the absorbance at 275 nm.

The sedimentation of the beers was determined at temperatures of 4 °C and 25 °C to simulate refrigeration and room-temperature storage conditions. For this, 2 g of the sample was added to a microtube and centrifuged at 14,000 rpm for 5 min. The supernatant was discarded, and the percentage of sedimentation was calculated using the initial amount of the sample (g) and the mass determined after centrifugation [29].

The color of the craft beers was determined using a Color test II spectrophotometer (Hunter lab, Reston, VA, USA) and by measuring the color parameters L* (brightness), a* (red–green tone), and b* (yellow–blue tone). The hue angle (h°), which provides a qualitative measure of color attributes, was determined using Equation (2). The chroma index (C*), a quantitative measure of color, was computed as per Equation (3).

h° = tan⁻¹ (b*/a*)

(2)

C* = (a*² + b*²)1/2

(3)

In addition, the European Brewery Convention (EBC-Method 9.6) was used to read the absorbance of the diluted samples against a water blank on a UV-5100 UV/Vis Spectrophotometer (Metash) at 430 nm (${\mathrm{A}\mathrm{b}\mathrm{s}}_{430\mathrm{n}\mathrm{m}})$. The results were calculated using Equation (4) and were expressed in color units [30].

$$\mathrm{EBC}\left(\mathrm{c}\mathrm{o}\mathrm{l}\mathrm{o}\mathrm{r} \mathrm{u}\mathrm{n}\mathrm{i}\mathrm{t}\mathrm{s}\right)=25\times \mathrm{d}\mathrm{i}\mathrm{l}\mathrm{u}\mathrm{t}\mathrm{i}\mathrm{o}\mathrm{n} \mathrm{f}\mathrm{a}\mathrm{c}\mathrm{t}\mathrm{o}\mathrm{r}\times {\mathrm{A}\mathrm{b}\mathrm{s}}_{430\mathrm{n}\mathrm{m}}$$

(4)

2.2.4. Bioactive Characterization

Preparation of Extracts

The extracts for the analysis of bioactive compounds (anthocyanins and total phenolic compounds) and antioxidant activity (ABTS, DPPH, and FRAP methods) were prepared according to the methodology proposed by Larrauri et al. [31]. For this, 100 µL of the samples was pipetted and sequentially extracted with ethanol/water (50:50, v/v) at room temperature for 1 h without light. The supernatant was then recovered, and a mixture of acetone/water (70:30, v/v) was added to the residue and subjected to a new extraction under the conditions mentioned previously. The extracts from the ethanol and acetone extractions were combined and stored at −4 °C in the dark for later analysis.

Total Phenolic Compounds

Total phenolic compounds (TPC) were determined according to the methodology described by Folin and Ciocalteu [32], with some modifications proposed by Almeida et al. [33]. The analysis was performed in 96-well microplates, using a mixture of 10 µL of the craft beer samples (1:6) and 200 µL of Folin–Ciocalteau reagent (1:10, v/v). After 3 min, the reaction was stopped by adding 100 µL of sodium carbonate (20%, w/v). Absorbance was measured at 765 nm with a spectrophotometer. The standard curve was obtained with gallic acid, and the results were expressed in mg gallic acid/L of the sample (mg GAE/L).

Total Anthocyanins

Total anthocyanins were determined using the differential pH method described by Lee et al. [34]. The extracts were diluted in two buffer solutions with pH 1.0 and pH 4.5. Absorbance was determined at 510 nm and 700 nm using a spectrophotometer. The total anthocyanin content of the extracts was calculated using Equations (5) and (6).

A = (A_510nm − A_700nm) pH_1.0 − (A_510nm − A_700nm) pH_4.5

(5)

$$\mathrm{T}\mathrm{A}\mathrm{C}={{\displaystyle \frac{\mathrm{A}\times \mathrm{M}\mathrm{W}\times \mathrm{D}\mathrm{F}\times 10}{\mathsf{ϵ}\times 1}}}^3$$

(6)

where TAC corresponds to the total anthocyanin concentration, A corresponds to the absorbance calculated by Equation (5), MW is the molecular weight of cyanidin-3-glucoside (449 g/mol), DF is the dilution factor, and ε is the molar extinction coefficient (L/mol⁻¹/cm⁻¹). The results were expressed in mg of cyanidin-3-glucoside equivalent per L.

Flavonoids

The total flavonoid content was determined using colorimetry, following the method described by Subhasree et al. [35]. A quantity of 250 mL of sample was mixed with 1.5 mL of distilled water and 150 mL of a 5% (m/v) sodium nitrite solution. After 5 min, 300 mL of a 10% (m/v) aluminum chloride hexahydrate solution was added to the mixture, which was then homogenized and left at room temperature (25 °C) for 6 min. Next, 1.0 mL of 1M sodium hydroxide was added, and the volume was adjusted to 5 mL. The absorbance of the mixture was measured at 510 nm. Quercetin was used as the standard, and the results were expressed as g of quercetin per 100 mL of beer (on a wet weight basis).

Antioxidant Activity (ABTS, DPPH, and FRAP Methods)

The ABTS method was carried out by reacting 5 mL aqueous ABTS solution (7 mM) and 88 μL potassium persulfate solution (140 mM) to produce the ABTS radical cation (ABTS⁺), which was kept in the dark for 16 h. The ABTS radical was diluted with ethanol to absorb 0.7 ± 0.05 at 734 nm. In the dark, 15 μL of the samples was added to 1500 μL of ABTS radical solution, and after 6 min, the absorbance at 734 nm was measured [36].

The DPPH method was carried out by reacting 45 μL of the sample with 1800 μL of 60 μM 2,2-diphenyl-1-picrylhydrazyl in the methanol solution. After a 30 min incubation in the dark, the absorbance was measured at 515 nm. The results were expressed in μM of Trolox equivalents [36].

The FRAP method was carried out by preparing the FRAP reagent (1 mL of TPTZ (10 mM), 1 mL of FeCl₃ (20 mM), and 10 mL acetate buffer (300 mM), pH 3.6) in the dark. The reaction was carried out by mixing 15 μL of the sample with 285 μL of the FRAP reagent. After 30 min of incubation in the dark, the absorbance was measured at 593 nm, and the results were expressed in μM of ascorbic acid equivalents [37].

2.2.5. Sensory Analysis

Sensory analysis protocols were approved by the Research Ethics Committee (No. 3300322). The analysis was performed in individual offices of the Sensory Analysis Laboratory of the Instituto Federal Goiano, Rio Verde, Goiás, Brazil. Among the participants, 67% were male and 33% were female. Participants were given approximately 20 mL of each craft beer at a temperature of <7 °C. The samples were presented in a monadic and balanced manner to each of the 12 participants.

The CATA (check-all-that-apply) variant of the EsSense Profile^® questionnaire with 39 emotion words was used to evaluate product-focused emotion research [38]. The evaluated terms were: “active”, “adventurous”, “affectionate”, “aggressive”, “bored”, “calm”, “daring”, “disgusted”, “eager”, “energetic”, “enthusiastic”, “free”, “friendly”, “glad”, “good”, “good-natured”, “guilty”, “happy”, “interested”, “joyful”, “loving”, “merry”, “mild”, “nostalgic”, “peaceful”, “pleasant”, “pleased”, “polite”, “quiet”, “satisfied”, “secure”, “steady”, “tame”, “tender”, “understanding”, “warm”, “whole”, “wild”, and “worried”. The emotional profile was assessed in three parts.

First, the emotion profile for grape pomace craft beer was evaluated before and after reading texts about grape health benefits (text 1) and the use of by-products and sustainability (text 2) to see how they could change the emotions of potential consumers. Text 1 was as follows: “The beverages you consumed contain part of grapes. Recently, research has shown that grapes and their fractions may contain active compounds beneficial to human health, especially due to their high content of compounds called flavonoids, which have high antioxidant activity”. Text 2 was as follows: “Furthermore, we inform you that the drink you consumed contains grape pomace which is a by-product of the manufacture of grape juice. In addition to contributing to the nutritional aspect and potentially beneficial to health, using grape pomace can reduce the environmental impact of producing grape juice by using a valued by-product (grape pomace). As long as they are produced and handled correctly, consuming grape pomace in other food products is a tasty, healthy, and safe alternative and does not result in health risks”. Following the reading of the texts, the participants filled out CATA EsSense Profile^® questionnaires.

Second, participants received all the grape pomace craft beers, labeled with three-digit numbers, served monadically and randomly assigned, and evaluated the CATA EsSense Profile^® of each sample. The purchase intention for each sample was evaluated immediately afterward, ranging from (1) certainly would not buy to (5) certainly would buy, and expressed as a percentage by score.

Third, participants were asked what the best ways to offer products based on grape by-products would be, and the comments were evaluated qualitatively, as they were descriptive highliners.

The frequency of use of each term was determined by counting the number of consumers who checked that term to describe each beer sample. Cochran’s Q test was performed to identify significant differences among samples for each emotional perception (second step). A Correspondence Analysis (CA) was used to analyze the association between the CATA EsSense Profile^® results and the beer samples using matrix data (second and third stages).

In addition, Correspondence Analysis (CA) was performed on the total frequency count of emotions in each condition (blind and informed about health benefits [text 1] and sustainability [text 2]) to identify relationships among them [39]. Following this, the global chi-square test was employed to assess the independence between rows and columns, which could verify differences between emotional profiles and the impact of information on different emotions.

2.2.6. Statistical Analysis

All experiments were performed in triplicate, and all analyses were performed in triplicate. Results were expressed as average values ± standard deviations. The average values of all experiments were evaluated using analysis of variance (ANOVA) and Tukey’s mean test at a 5% significance level (p ≤ 0.05) with the Statistica 7.0 software (version 8.0, StatSoft).

3. Results and Discussion

3.1. Physicochemical and Bioactive Characterization of Grape Pomace from Grape Juice Production

Table 1. Physicochemical (wet basis) and bioactive characterization of grape pomace from grape juice production.

Component	Wet Basis	Dry Basis
Moisture (%)	78.27 ± 0.35	-
Protein (%)	1.30 ± 0.20	6.56 ± 0.37
Ash (%)	0.65 ± 0.04	3.00 ± 0.17
Ether extract (%)	1.48 ± 0.05	6.85 ± 0.22
Carbohydrates (%)	18.17 ± 0.41	84.08 ± 0.79
Energetic value (kcal)	91.22 ± 1.12	424.34 ± 3.84
pH	4.29 ± 0.10	-
Total titratable acidity (%)	6.65 ± 0.09	-
Total phenolic compounds (mg GAE/L)	3866.23 ± 1.45	-
Total anthocyanins (mg of cyanidin-3-glucoside/L)	1368.37 ± 74.60	-
FRAP (mg of ascorbic acid/L)	6499.03 ± 11.36	-
ABTS (µM Trolox/L)	43,311.37 ± 13.44	-
DPPH (µM Trolox/L)	33,549.36 ± 5.69	-

provides a comprehensive physicochemical and bioactive characterization of grape pomace derived from grape juice production, analyzed wet and dry. The results indicate that grape pomace is notably rich in carbohydrates, containing 18.17% on a wet basis and 84.08% on a dry basis. This high carbohydrate content suggests that grape pomace can be a valuable source of fermentable sugars, potentially enhancing ethanol production by yeast during fermentation. Conversely, grape pomace exhibits relatively low concentrations of proteins (1.3% on a wet basis and 6.56% on a dry basis), ash (0.65% on a wet basis and 3.99% on a dry basis), and ether extract (1.48% on a wet basis and 6.85% on a dry basis).

The fresh grape pomace used in the fermentation process for producing bioactive beer demonstrated a high moisture content (78.27%), necessitating immediate processing due to its implications for raw material utilization. The elevated water content poses a significant limitation for preserving grape pomace, as it can facilitate microbial growth and initiate chemical and enzymatic reactions. These factors can adversely affect the raw material’s safety, shelf life, and nutritional, bioactive, and sensory properties [40].

The obtained results vary from those documented by Machado et al. [41] for grape pomace from the ‘Vinhão’ cultivar, which reported (%) 8.20 ash, 3.38 lipid, 9.85 protein, and 35.47 carbohydrate contents and a pH of 3.69. Furthermore, these findings differ from those observed in GP samples from two distinct Portuguese regions, Alentejo and Ribatejo, which exhibited ash contents ranging from 3.69% to 7.93%, proteins at trace levels, and pH values between 3.77 and 4.52 % [42]. Additionally, the results are distinct from those reported by Pereira et al. [43] for GP derived from the Touriga Nacional and Arinto varieties (Vitis vinifera L.), which recorded protein levels between 8.38% and 10.13%, polyunsaturated fatty acids ranging from 5.18% to 6.66%, soluble dietary fiber contents between 1.7% and 14.3%, and insoluble dietary fiber contents from 46.4% to 55.1%.

As reported in various studies, the variability in the physicochemical composition of GP is attributed to factors such as grape species, cultivation conditions, soil types, climatic conditions, processing methods, and pressing and preparation techniques [44]. All of these factors directly influence the physical and chemical composition of beer. Furthermore, the products to which the by-product will be applied (beverages and food) may also undergo some variability in their physical and chemical compositions. Therefore, it is very important to know the composition of the by-product, especially when adjusting the quality parameters during the fermentation process of beer production. Thus, appropriately carrying out the processing, transportation, and storage of the by-product is essential to preserve its nutritional, sensory, and bioactive components until they are incorporated as an ingredient in the beer production process. This diversity highlights the importance of understanding the composition of grape pomace to optimize the utilization of its components, which not only enables the development of consistent and high-quality products that meet consumer expectations but also contributes to the sustainability of the production chain and the reduction of environmental impacts.

Grape pomace contains various bioactive compounds that can positively impact technological and sensory aspects and, most importantly, benefit health. In this regard, grape pomace has been identified as a rich source of phenolic compounds (3866.23 ± 1.45 mg GAE/L). Phenolic compounds are key plant metabolites with antioxidant, antihypertensive, antimicrobial, and anticancer properties. They are used in food to prevent lipid oxidation and control microbial growth and in pharmaceuticals and cosmetics for products like mouthwashes, eye creams, and herbal cosmetics. The main phenolic compounds in GP are anthocyanins, flavonoids (like quercetin and kaempferol), phenolic acids (caffeic and ferulic acids), and resveratrol [10,45].

Another important set of bioactive compounds in grape pomace are anthocyanins (1368.37 mg of cyanidin-3-glucoside/L). Anthocyanins are natural pigments in many plants, imparting red, purple, and blue colors. Beyond their sensory role, they provide various health benefits, including antioxidant and anti-inflammatory properties, support for cardiovascular health, and potential reductions in the risk of type II diabetes and certain cancers [46,47]. Although their absence does not cause disorders in the body, regular and moderate consumption of beverages enriched with these compounds can enhance their benefits, supporting physiological aspects and overall health throughout life [48].

Since there is no universal standard for consumption and intake recommendations, dosages of anthocyanins can vary worldwide, with various studies suggesting specific amounts for achieving desired effects. For example, China recommends a daily intake of 50 mg per person to promote positive effects, such as reducing oxidative stress levels, cancer risk, metabolic syndromes, diabetes, and other health conditions [49]. Furthermore, 80 mg/day or higher of purified anthocyanins have demonstrated antioxidant and anti-inflammatory effects in a randomized clinical trial [50]. The recommended dose of anthocyanins can vary depending on the therapeutic objective and the individual’s health status, age, and sex. Additionally, the variation in doses used in studies and recommendations reflects the need for individual adjustments to optimize therapeutic effects and address personal specifics [47,51].

In addition to anthocyanins, a high concentration of antioxidant compounds has been observed. These can act as neutralizers of oxidation reactions and prevent oxidative processes in the human body and the matrices where they are applied. Grape pomace demonstrated high antioxidant activity across all three methods employed, including the FRAP (6499.03 mg of ascorbic acid/L), ABTS (43,311.37 µM Trolox/L), and DPPH assays (33,549.36 µM Trolox/L). Among the antioxidant compounds commonly found in grape processing by-products, polyphenols such as anthocyanins, flavonols, flavan-3-ols, and proanthocyanidins are particularly noteworthy. Additionally, phenolic acids, resveratrol, and dietary fibers are significant components. These compounds are crucial in neutralizing free radicals, protecting against oxidative stress, improving health, and reducing the risk of various diseases. Grape pomace, a common by-product of winemaking, is particularly rich in these antioxidants, making it a valuable resource for nutritional and functional applications [52].

In addition to its use in food and beverages, grape pomace has been repurposed for anthocyanin extraction [46] and used in cosmetics [53], as well as for food production [12]. This practice adds value to a by-product of the juice industry and contributes to sustainability by reducing waste and minimizing the environmental impacts of pomace disposal.

3.2. Physicochemical, Technological, and Color Characterization of Craft Beer Added with Grape Pomace

Table 2. Technological characterization and color profile of craft beers produced with grape pomace from grape juice production.

Analysis/Samples	Control	1%	5%	10%
pH	4.08 a ± 0.06	4.08 a ± 0.07	4.01 ab ± 0.05	3.94 b ± 0.05
Soluble solids (°Brix)	5.26 b ± 0.11	6.48 a ± 0.10	6.40 a ± 0.06	6.35 a ± 0.03
Total titratable acidity (%)	2.56 ± 0.31 b	2.69 b ± 0.15	2.85 ab ± 0.17	3.13 a ± 0.17
Alcohol content (%)	3.8	5.5	5.43	5.43
Bitterness (IBU)	28.57 a ± 1.50	27.30 a ± 1.40	15.00 b ± 0.43	16.66 b ± 0.84
Beer foam (cm)	2.75 a ± 0.25	1.83 b ± 0.15	1.4 b ± 0.15	0.95 c ± 0.05
Density (g/mL)	1.0209 b ± 0.00	1.0256 a ± 0.00	1.0251 a ± 0.00	1.0250 a ± 0.00
Sedimentation at 25 °C (%)	2.06 a ± 0.08	2.88 b ± 0.20	3.27 b ± 0.12	3.76 b ± 0.17
Sedimentation at 4 °C (%)	1.93 a ± 0.17	2.49 b ± 0.01	2.64 b ± 0.18	3.40 c ± 0.20
Dry extract	3.42 c ± 0.12	3.70 a ± 0.08	3.62 ab ± 0.01	3.43 bc ± 0.01
Color (EBC)	14.99 d ± 0.03	19.41 c ± 0.03	21.01 b ± 0.03	22.50 a ± 0.03
L*	81.15 d ± 1.86	74.85 c ± 2.61	70.54 b ± 0.94	62.24 a ± 2.40
a*	−0.06 d ± 0.02	1.17 c ± 0.19	8.94 b ± 0.25	18.00 a ± 1.05
b*	3.13 b ± 1.27	8.22 a ± 2.62	8.33 a ± 0.4	10.11 a ± 0.86
c*	3.13 d ± 1.27	8.56 c ± 2.78	12.22 b ± 0.46	20.65 a ± 1.34
H	91.08 d ± 0.94	81.63 c ± 1.66	42.98 b ± 0.61	29.29 a ± 0.70

Means on the same line with different lowercase letters are significantly different (Tukey’s test, p < 0.05).

presents the technological characterization and color profile of craft beers produced with varying concentrations of grape pomace derived from grape juice production. Additionally, Figure 1 presents the visual appearance of the control beer (without the addition of grape pomace) (Figure 1A) and beers with 1% (Figure 1B), 5% (Figure 1C), and 10% grape pomace (Figure 1D). In general, the addition of grape pomace affected the beer’s technological parameters and color profile, with these changes becoming more pronounced as the concentration of grape pomace increased.

The bitterness of beer, measured in International Bitterness Units (IBU), quantifies the concentration of alpha-acids extracted from hops during the wort heating process, which are responsible for its characteristic bitterness. The IBU level is influenced by the quantity and type of hops used and the timing of their addition during production. It significantly balances the malt’s sweetness with the beer’s overall flavor profile [54,55].

In the present study, the addition of grape pomace reduced bitterness, particularly in beers with 5% and 10% GP (15.0 and 16.6 IBU, respectively), compared to the control beer and the beer with 1% grape pomace (28.5 and 27.3 IBU, respectively). This reduction may be attributed to the dilution of alpha-acids or the binding of iso-alpha-acids with proteins that did not precipitate during wort heating [56] or even to their binding with components of the grape pomace, which are removed during the separation of solid material for clarification and bottling. Various studies have demonstrated that grape pomace has a high capacity for adsorption and binding with various components [57,58].

Foam in beer is a crucial technological parameter with significant physical and sensory effects on the product. It consists of a layer of carbon dioxide bubbles trapped in a matrix of proteins and other compounds. This foam, generated by natural or forced carbonation, is essential for perceiving beer quality, influencing appearance, texture, and aroma retention and protecting against oxidation [59,60].

Among the craft beers produced, the control beer (without GP addition) exhibited the highest foam formation (2.75 cm). As the concentration of grape pomace in the beer formulation increased, foam formation decreased significantly, with beers containing 1%, 5%, and 10% grape pomace showing foam heights of 1.83 cm, 1.4 cm, and 0.95 cm, respectively.

The reduction in foam formation in beer can be attributed to several factors, mainly ethanol and lipids. Ethanol is a significant compound that negatively affects foam; concentrations above 3% can interfere with foam formation and stability. Similarly, lipids prevent the proper binding of foam-stabilizing components, hindering the formation of a stable matrix [59].

Beers produced with the addition of grape pomace exhibited higher alcohol contents compared to the control beer (3.8%, 5.5%, 5.43%, and 5.43% for the control beer and beers with 1%, 5%, and 10% grape pomace, respectively). The supplementation with grape pomace appears to have introduced fermentable sugars metabolized by the yeast, thereby contributing to increased ethanol production [13]. The higher alcohol content and other chemical components from the grape pomace, such as lipids, may explain the foam formation reduction in beer incorporating grape pomace during fermentation.

Another important factor in foam formation and stability is pH, and, consequently, the beverage’s acidity. These factors can influence the protein structure and the stability of the matrix that retains CO₂ in the beer [59]. In this case, the beer with 10% grape pomace addition, with a pH of 3.94, exhibited a lower pH value and a higher total titratable acidity (3.13) compared to the control beer, which had a pH of 4.08 and a total titratable acidity of 2.56%. The lower pH of the beer with the addition of purple GP is related to the presence of organic acids, mainly tartaric, malic, citric, and acetic acids, which can promote greater acidification and a decrease in the pH of the beer when they are extracted during the fermentation process [14,15].

The soluble solids (SS) values were significantly higher in the craft beers with added grape pomace (1%GP: 6.48 °Brix, 5%GP: 6.40 °Brix, and 10%GP: 6.35 °Brix) compared to the control beer (5.26 °Brix). This increase could influence sensory properties and the fermentation process, and it also appears to have contributed to the observed sedimentation. Sedimentation in beer quantifies the sediments that accumulate at the bottom of a container after the beer has been subjected to a specific gravitational force under conditions simulating storage at refrigeration and ambient temperatures. This can indicate the amount of particulate material from autolyzed yeast during the maturation period, as well as proteins, phenolic compounds (both free and complexed forms), and other solids that were not completely removed during filtration or clarification steps in the production process [30,61]. Sedimentation and the presence of particles impact the sensory and technological aspects of beverages, as they affect visual appearance, turbidity, and, consequently, the clarity of the drink. These factors are among the most important considerations during consumption [30].

In this study, beers with grape pomace addition during fermentation exhibited higher sedimentation levels, regardless of temperature. However, a temperature of 25 °C resulted in higher sedimentation percentages. The grape pomace concentration significantly (p < 0.05) raised sedimentation levels, with the highest sedimentation values observed at 25 °C (control: 2.0%; 1% GP: 2.8%; 5% GP: 3.2%; 10% GP: 3.7%) followed by 4 °C (control: 1.9%; 1% GP: 2.4%; 5% GP: 2.6%; 10% GP: 3.4%).

Temperature affects the sedimentation rate in beer, as lower temperatures increase viscosity and slow down sedimentation, while higher temperatures decrease viscosity and accelerate the sedimentation of particulate matter. Additionally, smaller particles can result in slower and less noticeable sedimentation than larger particles of the same density due to the viscosity [62].

Additionally, as indicated by the percentage of dry extract, beers with grape pomace incorporation showed significantly (p < 0.05) higher levels of dry extract (1% GP: 3.7%, 5% GP: 3.62%, and 10% GP: 3.43%) compared to the control (3.42%). This suggests the presence of more solid material and, consequently, more significant interference in sedimentation.

The luminosity (L*) parameter was altered by incorporating grape pomace during fermentation. The parameter L* in color analysis represents the luminosity or brightness of the sample. It quantifies the intensity of light reflected by the sample, providing information about how light or dark the sample is [63].

The control sample exhibited the highest luminosity (81.15), while luminosity progressively decreased with the addition of 1% (74.85), 5% (70.54), and 10% (62.24) GP. The decrease in luminosity can be attributed to the pigments in the grape pomace, which are transferred from the solid fraction to the liquid, resulting in beverages with more intense colors, including anthocyanins, tannins, and other components (total anthocyanin contents are shown in

Table 3. Bioactivities of craft beers produced with grape pomace from grape juice production.

Analysis/Samples	Control	1%	5%	10%
Total phenolic compounds (mg GAE/L)	181.56 d ± 1.48	270.17 c ± 4.71	294.45 b ± 1.08	308.10 a ± 2.00
Total flavonoids (g of quercetin/L)	0.0411 d ± 0.0	0.0441 c ± 0.0	0.0501 b ± 0.0	0.0542 a ± 0.0
Total anthocyanins (mg of cyanidin-3-glucoside/L)	3.76 c ± 0.32	30.34 c ± 4.7	515.34 b ± 9.32	754.59 a ± 17.74
FRAP (mg of ascorbic acid/L)	84.75 d ± 4.09	208.64 c ± 14.84	498.58 b ± 4.91	844.75 a ± 18.19
ABTS (µM Trolox/L)	2468.33 d ± 16.67	3031.81 c ± 15.56	3860.11 b ± 12.03	4294.52 a ± 6.60
DPPH (µM Trolox/L)	1044.82 d ± 4.24	1258.59 c ± 4.91	1456.52 b ± 6.06	1878.22 a ± 6.45

Means on the same line with different lowercase letters are significantly different (Tukey’s test, p < 0.05).

and are discussed later).

The parameter a* indicates colors on the green–red axis (positive values indicate a tendency toward red, while negative values indicate a tendency toward green). In contrast, the parameter b* indicates colors on the blue–yellow axis (positive values indicate a tendency toward yellow, and negative values indicate a tendency toward blue) [63]. The control beer (without grape pomace) had a negative value (−0.06), while the incorporation of higher concentrations of grape pomace (1%: 1.17, 5%: 8.84, and 10%: 18.0) increased the positive values, indicating a shift toward red hues. Similarly, the b* parameter also increased with the addition of grape pomace, rising from 3.13 in the control beer to 10.11 in the beer with 10% grape pomace.

The chroma parameter (C) was also significantly increased from the control sample (3.13) in the beers with 1%, 5%, and 10% grape pomace (8.56, 12.22, and 20.65, respectively), indicating that the addition of and increase in grape pomace concentration enhanced the color intensity of the beer. Finally, the hue parameter (h), calculated from the a* and b* parameters, decreased as the concentration of grape pomace increased in the samples (1%: 81.63, 5%: 42.98, and 10%: 29.29) compared to the control beer (91.08).

The addition of grape pomace to craft beers not only introduced unique and attractive color variations, altering the sensory profile of the beer, but also provided a sustainable option for incorporating bioactive compounds without the need for prior extraction of the components.

3.3. Bioactive Characterization

Table 3 presents the bioactivities of craft beers produced with grape pomace from grape juice production. In general, the addition of grape pomace altered the presence of bioactive compounds, such as total phenolics, anthocyanins, and flavonoids, and the antioxidant activity of the beers, with these changes becoming more evident as the concentration of grape pomace was increased.

Beers produced with grape pomace showed a significant increase (p < 0.05) in total phenolic content, with a proportional rise corresponding to the concentration of grape pomace, ranging from 181.5 m GAE/L in the control beer to 308.1 mg GAE/L in the beer with 10% grape pomace. The contents of flavonoids (from 0.04 to 0.05 g of quercetin per 100 mL of beer in the control beer and the 10% beer, respectively) and anthocyanins (from 3.7 to 754.5 mg of cyanidin-3-glucoside/L of beer in the control beer and the 10% beer, respectively) also followed this increasing trend. This enhancement is highly beneficial, as phenolic compounds, flavonoids, and anthocyanins possess valuable bioactive properties, such as antioxidant and anti-inflammatory effects and potential protection against chronic diseases, reinforcing the beverage’s functional value and health potential.

Various methods for evaluating the antioxidant activity of compounds in plants are available, as the components may have specific characteristics, and the methods must be able to assess this variability in compounds. Antioxidant activity methods such as FRAP, ABTS, and DPPH have distinct properties, allowing for a more comprehensive and detailed analysis of the antioxidant capabilities of compounds present in grape pomace. The varying antioxidant activity values obtained using ABTS, DPPH, and FRAP methods can be attributed to their different mechanisms of action, which help identify diverse antioxidant compounds. The FRAP method measures the sample’s electron-donating ability in an acidic environment, the ABTS method detects both lipophilic and hydrophilic antioxidants across a wide pH range, and the DPPH method assesses the neutralization of the DPPH radical, preventing chain oxidation reactions [64].

In this context, we used three methods to evaluate the antioxidant activity of grape pomace and beers incorporated with grape pomace during fermentation to confer bioactive properties. The beers produced with grape pomace exhibited higher antioxidant activity compared to the control (without grape pomace addition) in both methods used (FRAP: 84.75 mg of ascorbic acid/L, ABTS: 2468.3 µM Trolox/L, DPPH: 1044.8 µM Trolox/L). Additionally, higher antioxidant activity (p < 0.05) was observed in the beers containing 10% grape pomace (FRAP: 844.7 mg of ascorbic acid/L, ABTS: 4294.5 µM Trolox/L, and DPPH: 1878.2 µM Trolox/L). The higher antioxidant activity in the beers can be attributed to the presence of various bioactive compounds naturally found in the by-product, including anthocyanins, catechins, flavonol glycosides, phenolic acids, alcohols, and stilbenes [65], which have their solubility and extraction improved during the fermentation process due to the production of alcohol, an efficient solvent for extracting bioactive compounds [11], and can contribute to the transfer of components from the grape pomace to the beer. Other factors can also influence the transfer of bioactive compounds from grape pomace to beer. They may be mainly related to processes related to the grape, such as skin size and thickness, degree of maceration, and pomace pressing, in addition to the production of alcohol during the fermentation process that can extract phenolic compounds from the pomace, resulting in their migration to the beer [66].

Several studies in the literature report the use of commercial fruits in beer production as a means to diversify flavors and bioactivities, including the application of grapes [67], cherries, raspberries, peaches, apricots, plums, oranges, apples [68], quinces [69], omija fruit [70], and others. In general, the properties and bioactivities of beers produced with these commercial fruits showed significant dependence on the starting materials’ quantity and quality and the beer production process. In contrast, there are few reports on using fruit by-products to enhance beer’s physicochemical, technological, and sensory properties. To our knowledge, there are only reports of beers produced with by-products such as banana peels, rice hulls, riceberry, and coffee pulp, which contributed to the presence of phenolic compounds and more intense colors (reddish-yellow and a more turbid appearance) [71].

3.4. Sensory Analysis

Sensory evaluation is essential for craft beer developed with grape pomace, as it helps assess the impact of by-products on taste, aroma, and overall consumer satisfaction. Regarding the emotion profile provided by participants before (blind) and after reading about the beneficial effects that may be contained in craft beer and the potential use of grape pomace in food as a means of promoting sustainability, there was no significant difference between the emotion profile expressed by participants before and after reading text 1 or text 2 (p > 0.99).

Pereira et al. evaluated the sensory acceptability of probiotic cupuaçu beverages [72] and demonstrated that nutrition claims effectively increased the acceptability of these beverages. Although acceptability appears to be influenced by knowledge of beneficial effects, expressing emotions can be challenging, as demonstrated in the present study.

After the participants evaluated the developed grape pomace craft beers, the emotional profile expressed by the participants was evaluated using the CATA EsSense Profile^®. Figure 2 demonstrates the representation of samples in the first and second dimensions of the Correspondence Analysis (CA) of grape pomace craft beers. Eager, tender, and worried emotions were removed because it was impossible to calculate the Cochran values due to lack of representativeness.

The CA revealed the association between the samples (grape pomace craft beers) and the emotional attributes in the CATA EsSense Profile^®, which explained about 77.44%% of the original information in two dimensions (Figure 2). The first and second dimensions represented 45.72% and 31.72% of the total variability, respectively.

The control craft beer demonstrated a high association with interested, joyful, and merry emotions, while 1% craft beer demonstrated a high association with enthusiastic, energetic, and secure emotions. The 5% craft beer demonstrated an association with mild and nostalgic emotions, and the 10% craft beer demonstrated an association with affectionate and whole emotions. Emotions considered positive (joyful, merry, pleasant, good, peaceful, happy, glad, tame, and active) seemed to be associated with all samples, since they were found among the control, 1%, 5%, and 10% samples.

The purchase intention test demonstrated average values of 3.5, 3.3, 3.6, and 3.1 for the control, 1%, 5%, and 10% craft beers. This value was in the “would not purchase” range. In sensory analysis, purchase intention refers to the likelihood that consumers will buy a product after evaluating it sensory-wise. This metric is used to measure product acceptance and consumers’ willingness to purchase, serving as an important indicator of market success potential [73].

Participants claimed that demonstrating the nutritional values in products developed with grape pomace is more important than adverting to sustainability issues (related to using by-products) (25% vs. 10% of participants). In addition, suggestions regarding the development of food products indicated that alcoholic beverages such as beer seem to be a good use of by-products (33.34%) and inclusion in dairy beverages, bakery products, sweets and jams, capsule-type powder products, and juices was also mentioned.

Sensory analysis reveals that while flavors are crucial for the acceptance of a new beverage, precise information on nutritional value plays an equally important role in product development. Consumers increasingly seek beverages with appealing taste profiles and precise, reliable nutritional benefits. This dual focus ensures that new products meet sensory preferences and health-conscious demands, enhancing their overall market appeal and potential for success.

4. Conclusions

The study demonstrated the potential of grape pomace (GP), a by-product of grape juice production, as a valuable raw material for enhancing the bioactive properties of craft beers. Incorporating GP at 1%, 5%, and 10% (w/w) during the fermentation stage resulted in beers with higher levels of phenolic compounds, flavonoids, anthocyanins, and antioxidants, particularly at the 10% GP concentration. These bioactive compounds contribute to the health-promoting properties of the beers. Additionally, adding GP influenced the color characteristics of the beers, reducing brightness and enhancing color intensity.

Despite the benefits, increased sedimentation was observed due to GP’s higher particulate matter content. Sensory analysis revealed distinct emotional profiles associated with different GP concentrations in the beers, although participants did not significantly change their emotional responses based on information about the beneficial effects. Furthermore, participants prioritized nutritional information over sustainability considerations, suggesting a need for clear communication of the health benefits of such bioactive ingredients.

Overall, the utilization of GP in craft beer production is a promising strategy for enhancing the nutritional and sensory qualities of the beverage while also providing a sustainable solution for the disposal of grape juice by-products. This approach adds value to the final product and aligns with sustainable food production practices. Despite this, further studies are needed to investigate the production of beer with the addition of purple grape pomace on a larger scale, aiming to assess the technical and economic viability and the evaluation of shelf life.