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Article

Fermentation Process Effects on Fermented McIntosh Apple Ciders

by
Zhuoyu Wang
1,*,
Andrej Svyantek
1,
Zachariah Miller
1 and
Aude A. Watrelot
2
1
Western Agriculture Research Center, Montana State University, Corvallis, MT 59828, USA
2
Department of Food Science and Human Nutrition, Iowa State University, Ames, IA 50011, USA
*
Author to whom correspondence should be addressed.
Fermentation 2024, 10(3), 115; https://doi.org/10.3390/fermentation10030115
Submission received: 30 January 2024 / Revised: 16 February 2024 / Accepted: 17 February 2024 / Published: 20 February 2024
(This article belongs to the Special Issue Assessment of the Quality and Safety of Fermented Foods 2.0)
Browse Figures
Versions Notes

Abstract

:
This research is the first study of McIntosh apple cider fermentation using different must treatments. The must materials included standard pressed juice, the common cider fermentation material, mash, direct from the apple shredder both with and without pectinase additions, and finally, pomace. These four treatments caused multiple differences from the standard hard ciders from juice, starting with the apple must characteristics, following through the yeast fermentation processes, and carried into the final ciders. Initial apple musts had different sugar content, pH, acids, total phenolics, and antioxidant activities. Although juice contained more total phenolics and had more antioxidant capabilities, it contained lower levels of yeast assimilable nitrogen. The sugar consumption dynamic changes had a differential dynamic trend but did not alter the capacity for complete apple cider fermentation. From the fermentation color dynamic changes, it indicated that must materials would have effects on color-changing amplitudes. Juice treatment had the largest changes from the must. Pomace and mash with pectinase had fewer color changes in multiple color values (L*, a*, b*). The mono phenolics in the final cider indicated that pomace ferments contained the least hydroxycinnamates but a similar amount of total flavanols as juice-fermented ciders. Cider from the juice contained the least flavonols, whereas the mash, both with and without pectinase treatments, had the largest amount of flavonols. This work will provide some applicable information for apple cider fermentation from the apple wastes in the cider industry.

1. Introduction

The original trees of Mcintosh were discovered by John McIntosh, and horticulturist William Tyrrell Macoun was credited with popularizing this cultivar in Canada. Mcintosh apples were selected for their sweet-tart old-fashioned apple cider taste and aromas of honey, fruit, and spice. They are commonly cultivated in Canada, the United States, and Eastern Europe. Mcintosh apples are reported to have a significant decrease in total acidity with time of harvest [1]. With a three-week difference in harvest date, early Mcintosh contains high acidity with a citrus-like flavor, while late-harvested apples are sweeter and mellower. Mcintosh apple is among the most widely used cultivars for research, especially for winter hardiness and cloning [2]. This cultivar is also commonly used in apple breeding due to its pathogen resistance and winter hardiness [3,4].
McIntosh apple cider has been studied with other cultivars to compare varieties or cider technologies [5,6]. McIntosh apple cider showed inhibition of Escherichia coli bacteria growth compared with Golden Delicious and Melrose, even though its pH and °Brix did not have significant differences [6]. This indicated that McIntosh apple cider may contain some compounds which were not present in other cultivars. So far, only one research publication has applied treatment to McIntosh apple mashes by microwave processing [7]. Beyond this, electronic nose evaluations have been applied to discriminate volatile gas differences among intact apples and apple juice samples among Mcintosh and other two cultivars (Gala and Delicious) [8].
For cideries, apple musts with low pH, higher titratable acidity, high polyphenol content, and moderate to high YAN (yeast assimilable nitrogen) are common characteristics producers seek. For cider fermentation, sugar adjustment, selection of yeast strains, and temperature modification are the common strategies to improve cider must, impacting physicochemical characteristics and further influencing the cider aroma and flavors [9]. Beyond these methods, apple cider raw materials and pre-fermentation strategies can also influence the apple cider’s qualities.
In this apple cider fermentation research experiment, different apple materials, including juice, mash (whole fruit from the apple shredder), pectinase-treated mash, and pomace, were used. One of the must materials, freshly pressed juice is the most common and convenient material for cider fermentation [10,11].
Considering apples’ rank among the main fruits processed worldwide, after apple pressing to collect the juice, large volumes (approximately 25%) of by-products are generated, known as apple pomace [12,13]. Apple pomace, the left-over solid biomass, is, in fact, rich in carbohydrates, pectin, fiber, and minerals [14,15,16]. Apple pomace isolates can be used as a dietary supplement, functional food, or additives to benefit human health [12,15,17]. Adding apple pomace to cider increases phenolics and antioxidants, and apple pomace addition also influences the cider's sensory characteristics and color [18]. Pomace extract is also reported as a cider quality improvement method [19]. Therefore, in this research, pomace is one of the most used materials studied for McIntosh apple fermentation.
Apple mash, the ground products yielded directly from apples, is composed of juice and pomace with large amounts of both wet and dry materials. Mash can be treated with pectinase to destroy pectin and other dietary compounds [20]. In research and industry, pectinase has been used to clarify and increase apple juice extraction, even in the early 1980s [21]. It has been reported that pre-fermentation juice clarification can reduce unpleasant sulfur off-aroma in ciders. Pectinase clarification may change apple juice chemistry profiles, such as total nitrogen content, without changing the cider quality [22]. For fruit spirits, pectinase can contribute to higher methanol concentrations in the final products [23].
This study investigates cider fermentation from various materials: pomace, juice, and apple mashes. Further assessed is the influence on apple cider fermentation dynamics and final products. The cider products were characterized for basic cider physicochemical characteristics, phenolic content, and antioxidant activities. This research offers some suggestions for apple cider fermentation through pre-fermentation material choices and processes.

2. Materials and Methods

2.1. Apples and Apple Treatment

McIntosh apple trees were planted at the Western Agricultural Research Center of Montana State University, Corvallis, MT, USA, in 1878 by Amos Buck of the Bitterroot Valley. About 60 kg of McIntosh apples were harvested in October 2022 and stored in a walk-in cooler (0–4 °C, humidity > 95%) until they were shredded by an electric apple grinder (MuliMIX, Downey, CA, USA) for fermentation. After grinding, four treatments were applied to apple mashes in this study (Figure 1). In detail, four replicates of 3.5 kg of apple mashes were mixed with 1.5 g/L pectinase (Cellar Science, Eugene, OR, USA) and incubated overnight before fermentation. Three-quarters of apple mashes were allocated to non-pectinase treatment, which was further divided into three parts for fermentation, one-quarter of which was utilized for direct fermentation without pectinase treatment (3.5 kg of apple mash per fermenter). The final two-quarters of apple mash were pressed to create juice and pomace fractions. A bladder fruit press (Speidel, Providence, RI, USA) with 3 bar water pressure was used to generate apple pomace and apple juice. Four replicates of 3.5 kg pressed apple juice represented juice treatment for fermentation (Table 1). A total of 0.875 kg (25% × 3.5 kg) pomace was used as the main material for pomace treatment. Potassium metabisulfite (Morewine, Pittsburg, CA, USA) was added to each fermentation vessel at a rate of 50 ppm at the time of sample partitioning in order to increase microbial stability and prevent oxidation [24].

2.2. Fermentation

The fermentation experiments were conducted in 1.4-gallon glass Little Big Mouth Bubblers (Northern Brewer, Minneapolis, MN, USA). After collecting the initial, must samples for testing basic chemical compositions, including °Brix, pH, and acidity, corn sugar (2.27 kg/bag, Brewmasters, Pittsburg, CA, USA) was added to pomace treatment fermenters to adjust °Brix to 15. The commercial yeast strain Côt des Blancs (Red Star Yeast, Milwaukee, WI, USA) at a rate of 0.25 g/L was inoculated into each bubbler following rehydration in 1.25 times Go-Ferm Protect (Morewine, Pittsburg, CA, USA). All the fermentations were processed at room temperature (21–23 °C) for 12 days to 19 days. Each fermentation treatment was replicated four times for a total of sixteen experimental fermentations.
After no signs of continued fermentation were observed based on carbon dioxide evolution or density reduction, ciders were transferred into 750 mL clear Ferro glasses (MoreWine!TM, Concord, CA, USA) and corked after adding 50 ppm potassium metabisulfite.

2.3. Chemical and Chromatic Properties of Ciders

Pre-fermentation liquid portions of musts were taken before sugar adjustment and analyzed for total yeast assimilable nitrogen (YAN). Two assay results were added together to generate the total YAN; one part was primary amino nitrogen (K-PANOPA, Neogen, Lansing, MI, USA), and the other part was L-Arginine/Urea/Ammonia (K-LARGE, Neogen, USA). The original must solution was used for these two assays. Total YAN was calculated by the equation: YAN = YAN(K-LARGE) + YAN(PAN).
The fermentable sugars, including fructose, glucose, and sucrose, were monitored in must-liquid extract samples through K-SUFRG enzymatic kits (Neogen, USA), according to the manuals. Soluble solid content (SSC in °Brix) was monitored using a density meter DMA35 (Anto Paar, Ashland, VA, USA), while pH was assessed through a pocket pH meter (PAL-pH; Atago Co., Tokyo, Japan). Pre-fermentation malic acid, citric acid, and tartaric acids were analyzed with a K-LMAL malic acid assay kit, K-CITR citric acid assay kit, and K-TART tartaric acid kit (Neogen, USA).
During fermentation, cider from each fermenter of each treatment was collected into 1.5 mL microcentrifuge tubes to check fermentation color-changing dynamics. Samples were briefly centrifuged at room temperature to separate particles from the solution before testing. The visual spectra (from 380 nm to 700 nm with 1 nm interval) of samples were analyzed by using a SPECTROstarnano microplate reader (BMG Labtech, Cary, NC, USA) in Corning 96 well plates (SLS3922, Millipore Sigma, Burlington, MA, USA). Spectra were collected as a means of checking fermentation color dynamics. The color data was converted by the software ColorBySpectra [25]. The absorbance data was translated into CIEL*a*b color parameters. Illuminant D65 was the condition utilized for translation. The color information was reported with L* (lightness), a* (green-red), and b* (blue-yellow) and plotted by R 4.2.1. Core Team.
Final ciders were analyzed by FTIR wine analyzer (Lyza5000 wine, Anton Paar, Ashland, VA, USA) to collect estimated ethanol and glycerol levels using the base wine model. The titratable acidity of the final wine was analyzed according to AOAC methods [26,27]. The results were calculated as a percent (grams of malic acid equivalent/100 g). The equation was T i t r a t a b l e   A c i d i t y % = 0.1 N   N a O H   ×   0.0067 m L   o f   c i d e r   u s e d × 100 .

2.4. Total Phenolics Concentrations and Antioxidant Activities of Cider Musts and Final Ciders

Following the manufacturer’s manuals, total phenolics were quantified through the Folin Ciocalteu method with a polyphenol quantification assay kit (KB03006, BQC, Asturias, Spain). The outcome data were expressed as µg Gallic Acid Equivalent (GAE)/mL. Antioxidant activities of cider musts were determined through the 2,2-diphenyl-1-picrylhydrazyl radical (DPPH) free radical scavenging method (KF01007, BQC, Asturias). Original apple cider must or cider samples were used for DPPH assays and tested at the same time. The outcomes were expressed as Trolox Equivalent Antioxidant Capacity (TEAC µM/µL).

2.5. Monomeric Phenolic Compounds Concentrations

Monometric phenolic compounds of ciders were analyzed using a 1260 Infinity II HPLC (Agilent Technologies, Santa Clara, CA, USA) with a reverse-phase column (LiChrospher 100-5 RP18 250 mm × 4.0 mm, 5 μm, Agilent Technologies, Santa Clara, CA, USA), DAD (Agilent 1260 Infinity II DAD WR) (Agilent 1260 Infinity II FLD Spectra) as previously publications [28,29]. The mobile phases were 50 mM ammonium dihydrogen phosphate pH 2.6 (mobile phase A), 20% (v/v) mobile phase A in acetonitrile (mobile phase B), 0.2 M ortho-phosphoric acid in water, pH 1.5 (mobile phase C). The detailed gradient followed the previous publication [30]. The column temperature was maintained at 40 °C with a flow rate of 0.5 mL/min. 20 μL of sample was injected. The monomeric phenolics were identified and quantified at different wavelengths: 280 nm for flavanols, 316 nm for hydroxycinnamic acids, 360 nm for flavonols, and 520 nm for anthocyanins. Flavan-3-ols were quantified using (-)-epicatechin (E1753, Sigma-Aldrich, St. Louis, MO, USA), the reference standard, and expressed as epicatechin equivalent (eq.) mg/L. Hydroxycinnamic acids were quantified using caffeic acid (C0625, Sigma-Aldrich, USA) as the reference standard and expressed as caffeic acid equivalent mg/L. Flavanols were quantified using quercetin-3-O-glucoside (E4018, Sigma-Aldrich, USA) as standard and expressed as quercetin-3-O-glucoside equivalent mg/L.

2.6. Statistical Analysis

All experimental data were expressed as mean ± standard deviation (SD) of four biological replicates. Statistical analysis was conducted using R 4.2.1. Core Team (2023) [31]. The replicates (n = 4) were treated as a random effect, while treatments were assessed as fixed effects. One-way ANOVA followed by Tukey HSD test was used to determine if there were significant differences between the pectinase treatment, untreated mash, juice, and pomace. The 95% confidence level was used to determine the statistical significance. In detail, the lme4 1.1-31 package was used for fitting and analyzing models, emmeans 1.8.5 packages were used to estimate the marginal means [32]. Package ggplot2 was used to generate plots [33].

3. Results and Discussion

3.1. Pre-Fermentation Must Components

Generally, sucrose and fructose contributed the largest amount to the total fermentable sugar in the differing McIntosh cider musts before sugar adjustment (Table 2). Glucose contributed the smallest amount among the three types of sugar. Pectinase-treated must, apple mash, and apple juice contained similar concentrations of total sugar (individual samples with ranges around 110–147 g/L). The pomace treatment contained only about 39.43 g/L sugar, which is about a quarter of the sugar from other treatments. Although there were no significant differences (p < 0.05) from the total sugar among pectinase, mash, and juice treatments, the extraction rate from each type of simple sugar showed variations. Glucose from juice and mash both had moderate amounts (about 6 g/L), whereas the pectinase treated must contain the maximum amount of glucose, which was approximately 9 g/L. This was expected since pectinases constitute a group of enzymes that break down complex polysaccharides [34]. This phenomenon slightly changes with less sucrose; greater levels of glucose availability following pectinase treatment have also been observed in other fruits [35]. Fructose from pectinase, mash, and juice must be about the same (around 70 g/L), and the pomace contained the least amount of fructose, only around 23 g/L. Also, pomace had the lowest amount of sucrose, while other musts contained similar amounts of sucrose (around 40–50 g/L). The sugar components indicated that pectinase could influence the glucose amount, although the must was only tested after overnight treatment with pectinase. The small amount of glucose changes (about 3 g/L) in pectinase treatment compared to mash and juice treatment but did not influence the total amount of sugar in the musts. Pectinase treatment for juices in publications has been variable in treatment pH conditions, treatment time length, and treatment doses [20,36]. Optimizing conditions for pectinase treatments of McIntosh apple must warrant further exploration.
Malic acid is reported as the main organic acid in apples, taking up to 90% of the organic acids and influencing the fruit coloration, shelf life, and ripeness perception. Meanwhile, citric acid also contributes a small portion to mature apple organic acid profiles [37]. In this research, we observed malic acid as the prominent detectable acid, as expected (Table 3). Citric acid results indicated that mash contained the most citric acid, no matter whether it was with or without pectinase. Juice and pomace contained the least amount of citric acid, from 0.02 to 0.08 g/L of citric acid on average.
Nitrogen is among the primary growth-limiting nutrients for yeast growth and activity, influencing the fermentation processes [38,39]. The YAN amount in apple juice varies among apple cultivars, location, and field management but often falls below 140 mg N/L, which is considered a minimum requirement for healthy fermentation [36]. Low YAN can contribute to increased levels of hydrogen sulfide (H2S), a common off-aroma compound [39]. In this research, low amounts of YAN were detected, especially in pomace. Pectinase, mash, and juice-treated musts contained a slightly higher amount of YAN (about 10 mg N/L on average) but were still far lower than typical fermentation-recommended YAN amounts. There was a similarly low amount of YAN among treatments. Therefore, for McIntosh apple cider must, YAN supplementation may be extremely important for maintaining healthy fermentation.
Wine and cider quality indicators, such as color and taste, are largely influenced by phenolic compounds [40]. In our research, the apple cider must contain a variable amount of total phenolics among treatments. Juice seemed to contain the largest amount of total phenolics after wine pressing, which was approximately 450–500 µg GAE/mL, followed by the must of mash, pectinase, and pomace treatment. It is worth noting that while pomace added into the fermentation contributed about ¼ of the weight of mash or pectinase-treated mash, the phenolics exceeded ¼ of the total phenolics (200–300 µg GAE/mL) relative to pectinase or mash treatments at the beginning of fermentation. The distribution of phenolic compounds varied significantly, and McIntosh apple peel contributed 26% to 29% to the total phenolic content, generally lower than other cultivar peel contributions [41]. Since apple flesh and peels contain different qualities and quantities of phenolics and antioxidants, different amounts of apple mass would be expected to correlate with total phenolics in principle [42].
The apple cider must antioxidant capacities, as measured through DPPH assays, indicated that juice and mash with/without pectinase treatment soluble must show higher antioxidant activities compared to pomace treatment must. Surprisingly, considering the weight of pomace (a quarter of other mash treatments) used for pomace treatment ferments, pomace must have a high level of antioxidant activities in soluble must, which indicates apple pomace is a valuable source of antioxidants [43].

3.2. Fermentation Sugar Dynamic Changes

Pomace ferments received sugar adjustment on Day 1. The purpose was to adjust the sugar to a similar amount (about 15 °Brix) as the other three treatments. Therefore, °Brix changed from 5 to around 18, as depicted in Figure 2. The variation of °Brix as 18 instead of 15 might be driven by sampling variation and issues with ensuring added sugars are integrated into the solution early in the process. The ethanol in the final Pomace cider was not as high as might be expected (>9 vol%) but was 8.18 vol% (Table 4). After inoculation, all treatments showed expedited sugar reduction from Day 5. Sugar was generally reduced with the slowest speed in Pomace treatments. Juice and mash had similar trends of sugar dynamic changes. Sugar content achieved a minimum level by Day 14 within all the treatments.

3.3. Chromatic Dynamics during Fermentation

Investigating the relationship between fermentation days and chromatic changes during fermentation, apple ciders were analyzed for L* (lightness), a* (green/red), and b*(blue/yellow) values (Figure 3). Through the fermentation processes, the largest differences in lightness were observed in juice fermentation, which increased by 60–70 L* units from the start of fermentation, indicating the juice color became brighter and clearer during fermentation. This increasing trend was also observed in pectinase-treated ferments, although the changes were less drastic. Mash treatment fermentations had the darkest color with lightness values between 0 and 75. Cider from pomaces had a downward lightness shift as the color grew darker during the fermentation processes.
Meanwhile, green/red pigments could also be observed via shifts in a* values. Juice a* values had a large range (−5 to 15) of changes during fermentation, and the a* values decreased with fermentation. Pectinase and pomace had the lowest a* values, both had a* values around 0, and the changes during fermentation were smaller, within a 5 to 10 a* unit range. Fermentation in mashes showed a* value above 5 at the beginning and around 5 at the end. As lightness changes, juice also had the largest decreased changes of a* values, which indicates the loss of red pigment. Other treatments did not have a large range of a* value changes in this study.
The largest changes in b* values were observed in juice and pectinase treatment; both had decreasing b* values, indicating the yellow pigment decreased during fermentation in these two treatments, corresponding to their true colors in circles during fermentation. Mash-treated ciders had b* values around 30 in the end, whereas pomace and pectinase had only around 20 and 15 in b* values, indicating their lower level of visual yellow coloration.
Overall, fermentation with juice had the largest color changes during fermentation. Mash contributed stable but darker and browner cider. Pomace fermentation and pectinase-treated mash fermentation had a more stable color during fermentation, and pectinase, as juice fermentation, resulted in brighter yellow cider as their products.
Color is an important sensory factor and is the first impression to be observed in wine or ciders by humans; this often leads to consumption expectations and is correlated with quality [44]. Anthocyanin quantity and stability contribute to color and qualities in red wine and some fruit wines [45,46]. However, polyphenols and tannins are responsible for the yellow-orange color in apple juices [47,48]. Oxidization products derived from flavanol monomers and hydroxycinnamic acids play an important role in cider color and its storage [49]. French cider research indicates that the desired color in ciders is also consumer-dependent [50]. Apple pomace has been used in apple cider making to recover phenolic compounds. It has also been reported that ciders fermented with apple pomace were the lightest in color compared with juice-fermented ciders [18]. As shown in our research (Figure 3), apple pomace fermentation had a lighter color compared with mash and juice fermented cider. The lightest colors in our study were pectinase-treated mash fermented apple cider. The amount of mash used in fermentation in the four treatments did not directly correspond to the final cider colors.

3.4. Final Cider Characteristics

From the final cider characteristics in Table 5, mash with or without pectinase did not influence the sugar amount available for yeast fermentation. Resultingly, they had similar ethanol quantities in the final ciders. Juice, on the other hand, resulted in 7.91 ± 0.1 vol% of ethanol. Pomace-fermented ciders had the highest amount of ethanol due to sugar adjustment at the beginning; however, these were not significantly different from juice-fermented ciders.
From the result of titratable acidities in ciders, the methods contributed to the differences in acidities in apple ciders. Juice-fermented cider had the largest amount of titratable acidity, followed by pectinase-treated mash and mash-fermented ciders. This also indicated that pectinase breaking down the apple mash contributed to higher acidity in the final ciders compared to mash-fermented ciders. Pomace fermented ciders had 3.98 ± 0.15 titratable acidity, which was higher than a calculated ¼ of mash or pectinase treatment final acidity. This might indicate that more acids were soluble in the final ciders in pomace ciders. The pH in the final ciders was around 3.20 to 3.40, with higher pH in ciders from juice, pomace, and mash treatment, whereas lower pH (3.22 ± 0.04) was observed in pectinase-treated mash fermented ciders.
Glycerol is a compound in fermented ciders that has a favorable impact on wine and cider quality [51]. Yeast strains and apple cultivars impact the glycerol content. From this study, pomace had the greatest glycerol content in the final ciders, and it was significantly higher than other fermented ciders. This may stem from the associated higher degree of fermentable sugars and final ethanol content, indicating a potentially more favorable environment for yeast metabolism to produce glycerol as its by-products.
From the phenolic content result (Table 5), in final ciders, juice, and pectinase-treated mash, fermented cider contained the most phenolics, about 271.85 and 248.59 µg GAE/mL on average. Meanwhile, mash without pectinase had significantly fewer phenolics compared to ciders from juice and pectinase-treated mash. Pomace contained about 139.44 µg GAE/mL phenolics in the final cider, which was more than a quarter of the phenolic content of cider from juice or mash. This indicated that pomace, as a source of cider fermentation, had the potential to extract more phenolics from apples. Meanwhile, compared to the corresponding phenolics in cider must (Table 4), the total phenolic content changes were minimal in ciders from juice and mash with or without pectinase treatment. Pomace must and cider had the maximum phenolic changes, more than 50 µg GAE/mL on average.
The final cider DPPH results indicated that although pomace used only a quarter of pomace for fermentation, its cider antioxidant activities were not significantly different from mash with/ without pectinase-treated ciders. Juice-fermented cider showed the highest antioxidant activities (about 90.09 TEAC µM/µL) compared to the other three treatments. Meanwhile, final cider antioxidant activities were largely increased in pomace and mash treatment compared to the cider must antioxidant activities (Table 4), increasing about 10 and 13 TEAC µM/µL per se. This might indicate that without pectinase, mash treatment ferment antioxidants can be improved through fermentation.

3.5. Cider Monomeric Phenolics

Three groups of monomeric phenolic compounds were quantified by HPLC-DAD. The four treatments caused large differences in each group of monomeric phenolic compounds (Figure 4). The flavanols, or flavan-3-ols, as the functional monomers or oligomers, play important roles in platelet aggregation, vascular inflammation, endothelial nitric oxide metabolism, and protective effects against neurodegeneration [52]. In the fermented products, juice and pomace fermented cider contained less flavanols compared to mash and pectinase-treated fermentation products. Flavanols were retained within the pomace after pressing, and extended contact with the pomace was needed to extract more flavanols for the final ciders. In ciders with juice treatment, the concentration of flavanols was the same as in the pomace treatment, indicating the flavanols remained in the pomace during fermentation.
Hydroxycinnamates, include chlorogenic acid, para-coumaric acid, caffeic acid, ferulic acid, sinapic acid, and their esterified/ esterified conjugate. This group of phenolics was reported as having the potential to reduce chronic diseases [53]. However, their bioavailability is determined by many factors, such as the type of hydroxycinnamates, chemical structures, doses, and human metabolism. The most hydroxycinnamates were detected in juice fermented cider through HPLC-DAD, followed by mash with and without pectinase. No difference was noted for hydroxycinnamates related to pectinase additions to mash. Pomace contained the least hydroxycinnamates, which was less than 10 mg/L. The juice cider contained more than five times of hydroxycinnamates compared to pomace cider.
The flavonols, a subgroup of flavonoids, are widely distributed in plants. Besides their antioxidant effects, they may also interfere with biochemical pathways, preventing certain diseases [54,55]. The flavonols were mainly detected in mash, with or without pectinase. Meanwhile, the pectinase treatment enhanced the total flavonols significantly compared to the mash treatment. Pomace contained about half the amount of flavonols of pectinase-treated ciders. The fermentation with juice only contained a small amount of total flavonols. This indicated that apple cider waste from mash or pomace could enhance the total flavonols in cider products.

4. Conclusions

This study showed that fermented McIntosh apple ciders from different base materials are affected in multiple dimensions. Compared to the standard apple cider from juice, each method showed its advantages. Pomace fermentation with only apple skins and pulps has very promising applications for cider fermentation or ciderkin production. Pomace apple cider showed a slightly darker color and fewer acids without compromising the amount of flavonols, but there was a higher amount of flavonols in the final cider products. Skin/pulp contact during fermentation with or without pectinase had similar amounts of flavanols and hydroxycinnamates between these two treatments. Pectinase-treated mashes produced brighter apple cider with higher flavonols and flavanols among the four treatments.
Concerning must, fructose was the main fermentable sugar among the most from different treatments, followed by sucrose and glucose. Before sugar adjustment, pomace had a different pH and Brix compared to the other three treatments. With mash, the must contain more yeast-assimilable nitrogen nutrients, although all musts were still far from desirable levels. Juice must have had the most total phenolics before fermentation, which were significantly different from other treatments. Pomace ferments contained less total phenolics and DPPH capabilities in the must.
Treatments caused differences in final cider characteristics. Pomace ferments largely influenced the acid and glycerol content in the final ciders. Although pectinase did not make differences in ethanol and glycerol content compared to the mash without pectinase treatment, it did cause significant differences in acids and pH of the final ciders. Juice, as the base cider must material, had different acidity and ethanol content compared to mash and pectinase treatments. Juice-fermented cider also had significant differences in pH and glycerol compared to pomace treatment ciders. Specific phenolic classes were largely variable based on treatments in final ciders.
This study provides useful information for apple cider fermentation, especially through exploring the use of waste materials in the juice and cider industry. The results suggest that pectinase, mash, and pomace can be useful for creating unique, sustainable apple cider fermented products. Each treatment had some advantages for fermentation. Depending on the customers’ preferences, these applied methods can be selectively employed for their desired purposes.

Author Contributions

Conceptualization, Z.W.; methodology, Z.W. and A.S.; investigation, Z.W., A.S. and A.A.W.; formal analysis, Z.W. and A.S.; resources and fruit collection, Z.M.; writing—original draft, Z.W.; writing—review and editing, Z.W., A.S., Z.M. and A.A.W.; funding acquisition: Z.W., A.S. and Z.M. All authors have read and agreed to the published version of the manuscript.

Funding

This research is funded by the Montana Department of Agriculture. Grant No.: 23SC00309.

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

The datasets generated and/or analyzed during the current study are available from the corresponding author on reasonable request.

Acknowledgments

The authors would like to thank Haydon Davis and the 2022 summer crew for assistance with farm maintenance. The authors would also like to thank Bridgid Jarrett and Kierstin Schmitt for the work coordination. We also thank Alexander D. Gapinski and Yiliang Cheng, for their help in the analysis of monomeric phenolic compounds in ciders.

Conflicts of Interest

The authors declare no conflicts of interest.

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Fermentation 10 00115 g001
Figure 1. McIntosh cider fermentation flow chart indicating partitioning of pectinase-treated mash, untreated mash, juice, and pomace.
Figure 1. McIntosh cider fermentation flow chart indicating partitioning of pectinase-treated mash, untreated mash, juice, and pomace.
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Figure 2. °Brix changes across the fermentation process by Days with four different McIntosh apple cider fermentation treatments. Except for pomace treatment with adjustment of sugar at the beginning, all the other treatments are without sugar adjustment. Day 1 of pomace indicated the soluble solids before sugar adjustment. Bars indicate the standard error of the mean for individual treatments, n = 4).
Figure 2. °Brix changes across the fermentation process by Days with four different McIntosh apple cider fermentation treatments. Except for pomace treatment with adjustment of sugar at the beginning, all the other treatments are without sugar adjustment. Day 1 of pomace indicated the soluble solids before sugar adjustment. Bars indicate the standard error of the mean for individual treatments, n = 4).
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Figure 3. Lightness (L*), Red/Green Value (a*), and Blue/Yellow (b*) changes during fermentation. Four different treatments are included in each plot: juice, mash, pectinase, and pomace treatments; each treatment contains four replicates. The Y-axis value indicates the specific values of L*, a*, or b*. The X-axis indicates the fermentation days (Day). The color of each dot indicates the must sample color through a 1 cm cuvette.
Figure 3. Lightness (L*), Red/Green Value (a*), and Blue/Yellow (b*) changes during fermentation. Four different treatments are included in each plot: juice, mash, pectinase, and pomace treatments; each treatment contains four replicates. The Y-axis value indicates the specific values of L*, a*, or b*. The X-axis indicates the fermentation days (Day). The color of each dot indicates the must sample color through a 1 cm cuvette.
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Figure 4. Monophenolic changes in McIntosh ciders. Four treatments for cider fermentation are Juice, Mash, pectinase-treated mash (Pectinase), and Pomace. Bars indicate the standard error of the mean for individual treatments, n = 4). The same letter above the error bars indicates no significant difference (p < 0.05).
Figure 4. Monophenolic changes in McIntosh ciders. Four treatments for cider fermentation are Juice, Mash, pectinase-treated mash (Pectinase), and Pomace. Bars indicate the standard error of the mean for individual treatments, n = 4). The same letter above the error bars indicates no significant difference (p < 0.05).
Fermentation 10 00115 g004
Table 1. McIntosh apple cider fermentation treatment basic materials.
Table 1. McIntosh apple cider fermentation treatment basic materials.
Treatment Pomace Weight (kg)Water Added (kg)Juice Weight (kg)Mash Weight (kg)Sugar Added (kg)
Pectinase---3.5-
Mash---3.5-
Pomace 0.875 (25% × 3.5 kg)Filled (~2 L) up to 3.5 kg--~0.47 (Targeted ~15 °Brix)
Juice --3.5--
Four treatments include pectinase-treated mashes (Pectinase), untreated mash (Mash), Pomace, and apple juice as original materials. Four repetitions are included in each treatment.
Table 2. Fermentable sugar content in apple must before sugar adjustment.
Table 2. Fermentable sugar content in apple must before sugar adjustment.
TreatmentD-Glucose (g/L)D-Fructose (g/L)Sucrose (g/L)Total Fermentable Sugars (g/L) 1
Pectinase9.00 ± 0.69 a67.69 ± 4.92 a39.78 ± 2.25 a116.46 ± 6.56 a
Mash5.88 ± 0.57 b70.65 ± 2.93 a48.00 ± 6.75 a124.53 ± 7.83 a
Pomace2.99 ± 0.21 c23.41 ± 1.83 b13.02 ± 0.78 b39.43 ± 1.70 b
Juice6.21 ± 1.63 b73.79 ± 4.95 a51.94 ± 12.85 a131.95 ± 15.32 a
1 The fermentable content includes D-Glucose, D-Fructose, and sucrose. Values are listed as mean ± standard error. Within each column, different letters indicate significant differences among treatments (p < 0.05).
Table 3. Pre-fermentation SSC (°Brix), pH, and acids.
Table 3. Pre-fermentation SSC (°Brix), pH, and acids.
Treatment°BrixpHMalic Acid (g/L)Citric Acid (g/L)
Pectinase15.03 ± 0.04 a3.64 ± 0.04 a4.95 ± 2.16 a0.21 ± 0.06 a
Mash14.85 ± 0.29 a3.63 ± 0.04 a4.32 ± 0.45 a0.19 ± 0.05 a
Pomace4.85 ± 0.46 b3.67 ± 0.03 a1.01 ± 0.28 b0.08 ± 0.034 b
Juice14.9 ± 0.36 a3.61 ± 0.03 a4.99 ± 1.58 a0.02 ± 0.05 b
Means followed by the same letter within columns are not significantly different (p < 0.05). Values are listed as mean ± standard error.
Table 4. Pre-fermentation YAN, total phenolics, and antioxidant capacities of musts.
Table 4. Pre-fermentation YAN, total phenolics, and antioxidant capacities of musts.
Treatment YAN (mg N/L)Phenolic Content
(µg GAE/mL)		DPPH Activity
TEAC (µM/µL)
Pectinase10.59 ± 4.36 a222.33 ± 29.70 bc73.48 ± 4.50 a
Mash10.30 ± 7.82 a286.90 ± 13.91 b71.32 ± 2.75 a
Pomace4.33 ± 1.93 a167.39 ± 4.07 c59.45 ± 12.46 b
Juice10.25 ± 7.18 a465.85 ± 27.49 a85.28 ± 10.72 a
YAN stands for Yeast Assimilable Nitrogen. Phenolic content is expressed as µg gallic acid equivalent to mL of juice extract. DPPH antioxidant capacity is expressed as Trolox Equivalent Antioxidant Capacity (TEAC µM/µL). Means followed by the same letter within columns are not significantly different (p < 0.05). Values are listed as mean ± standard error.
Table 5. Final cider ethanol, titratable acidity, pH, glycerol, and total phenolics.
Table 5. Final cider ethanol, titratable acidity, pH, glycerol, and total phenolics.
TreatmentEthanol (vol%)Titratable Acidity as Malic Acid (g/L)pHGlycerol (g/L)Phenolic Content
(µg GAE/mL)		DPPH
TEAC (µM/µL)
Juice7.91 ± 0.1 a7.46 ± 0.2 a3.30 ± 0.02 a4.67 ± 0.2 b271.85 ± 4.05 a90.09 ± 4.59 a
Mash6.26 ± 0.04 b5.54 ± 0.15 c3.34 ± 0.02 b5.17 ± 0.4 b215.72 ± 14.51 b84.06 ± 4.75 b
Pectinase6.11 ± 0.09 b6.47 ± 0.5 b3.22 ± 0.04 c4.87 ± 0.2 b248.59 ± 10.46 a73.77 ± 1.85 b
Pomace8.18 ± 0.17 a3.98 ± 0.15 d3.37 ± 0.03 ab5.93 ± 0.3 a139.44 ± 0.23 c69.52 ± 1.77 b
GAE indicates gallic acid equivalent. Phenolic content is tested through the Folin Ciocalteau method. Values are listed as means ± standard error of four replicates. Means followed by the same letter within columns are not significantly different (p < 0.05).
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Wang, Z.; Svyantek, A.; Miller, Z.; Watrelot, A.A. Fermentation Process Effects on Fermented McIntosh Apple Ciders. Fermentation 2024, 10, 115. https://doi.org/10.3390/fermentation10030115

AMA Style

Wang Z, Svyantek A, Miller Z, Watrelot AA. Fermentation Process Effects on Fermented McIntosh Apple Ciders. Fermentation. 2024; 10(3):115. https://doi.org/10.3390/fermentation10030115

Chicago/Turabian Style

Wang, Zhuoyu, Andrej Svyantek, Zachariah Miller, and Aude A. Watrelot. 2024. "Fermentation Process Effects on Fermented McIntosh Apple Ciders" Fermentation 10, no. 3: 115. https://doi.org/10.3390/fermentation10030115

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