Residual Sugar Research Articles

Development of a Novel Approach for Controlling and Predicting Residual Sugars in Wines

Residual sugars (RS) in wine are the sugars that remain in a wine after fermentation is complete. In some wine styles, such as semi-dry wines, the accurate measurement of the RS concentration is critical for both qualitative and legislative reasons. Brix, measured by a simple refractometer, can give a good estimation of the RS concentration in the must, but during fermentation, the presence of alcohol leads to inaccurate sugar measurements. In order to measure the RS accurately, other more precise techniques are used, most of which are expensive or require professional skills. Therefore, novel approaches for rapid, easy, and practical measurements for estimating the sugar content have been suggested over the years. However, most of these methods do not supply an actual measurement of RS but rather give brix values, and those that measure RS involve special equipment, which is less relevant for small wineries. This study suggests a novel model for predicting and controlling the wine’s residual sugar. The data the model uses is the initial brix of the must before fermentation and its density during fermentation. The model was created by measuring actual residual sugars during the fermentation of natural and synthetic musts, with various degrees of initial brix levels, while simultaneously measuring their densities and correlating the two measurements. Linear regression between the residual sugar of the wine and its density was obtained for all treatments and repetitions (i.e., different values of must initial brix) with R2 values above 0.97. Using the model, one can calculate (before commencing the fermentation) the density values at which the fermentation will reach a particular desired residual sugar value for a specific initial brix level; the model is applicable for the fermentation conditions used in this work, i.e., brix levels of 18–27 °Bx, Saccharomyces cerevisiae strains (fx-33 and fx-10) in common conditions of fermentation regarding temperature and aeration.

Lachancea thermotolerans fermentative metabolism is enhanced by chitosan under winemaking conditions

Wine industry is currently exploring different alternatives to sulphur dioxide as an antimicrobial agent, and chitosan is emerging as a highly promising option due to its multiple applications. In the context of climate change, the use of Lachancea thermotolerans to regulate pH and acidity levels during fermentation has become a promising alternative to other physicochemical approaches. This work analysed the impact of chitosan in sequential-mixed fermentations between L. thermotolerans and Saccharomyces cerevisiae. The presence of chitosan significantly affected the overall fermentation kinetics, resulting in faster fermentations and lower residual sugars, all without an increase in ethanol production. Wines produced under these conditions exhibited increased lactic acid levels (up to 50% more) and decreased malic acid content. This differences significantly influenced final pH (around 0.2 units) and acidity content (up to 1.65 g/L more) when compared to sulphur dioxide-supplemented controls. Chitosan also notably affected to other fermentative by-products, such as glycerol, contributing to improved wine complexity and quality. The addition of chitosan in wine fermentation impacted not only the fermentative performance of key non-Saccharomyces yeasts but the overall quality of the final product. This study provides new insights into the different effects of chitosan during the wine fermentative process.

Effect of exogenous organic acids on chemical compositions and sensory attributes of fortified sweet wines from dehydrated grapes

In this study, acidity was regulated with the addition of exogenous tartaric acid and citric acid before bottling. The effect of exogenous organic acids on chemical compositions and sensory attributes of fortified sweet wines from dehydrated grapes were investigated. The results indicated that exogenous organic acids promoted the conversion of monomeric anthocyanins to copigmented anthocyanins in wines. Specifically, the combination of malvidin-3-O-glucoside and flavanols (catechin and epicatechin) was facilitated to form copigmented anthocyanins. Sensory analysis suggested that exogenous organic acids improved the balance of sugar and acidity and benefited the harmony in wines on the taste. Wines with a residual sugar and titratable acidity ratio of about 11:1 exhibited the more harmonious taste. In addition, it was also observed changes in the aroma profile related to volatile compounds, namely, more intense fruity aroma in wines with the addition of organic acids.

Unmalted Cereals, Oenological Yeasts, and In-Bottle Sugar Addition as Synergic Strategies to Enhance the Quality of Craft Beers

Craft beer quality is the result of the complex interactions among ingredients. The purpose of this work was to assess the influence of combinations of cereal mixtures, yeast strains, and sucrose added for the refermentation in bottle on the physico-chemical and sensory characteristics of the resulting beers in order to maximize their antioxidant content and overall quality. More in depth, brewing trials were carried out with 16 combinations of 2 cereal mixtures (made of 60% malted barley/40% unmalted durum or soft wheat), 4 oenological Saccharomyces cerevisiae strains (17290 and 14061 isolated from Negroamaro; 9502 and 9518 from Susumaniello musts), and 2 concentrations of sucrose for refermentation (6 and 9 g/L). If maximizing the total phenolic content is the goal, the best beers were those obtained from the mixtures containing durum wheat and fermented by S. cerevisiae 17290 and 14061. Instead, the best sensory results were obtained from brewing the mixture containing the unmalted common wheat and fermented by S. cerevisiae 9518 thanks to their persistent foam; high turbidity, alcohol content, effervescence, and body; and low saltiness and sourness. The physico-chemical and sensory quality of beers were mainly affected by the cereal mixtures and secondarily by yeasts. The quantity of sucrose added for refermentation affected only CO2, residual sugar, and foam.

A previously unidentified sugar transporter for engineering of high-yield Streptomyces.

Sugar transporters have significant contributions to regulate metabolic flux towards products and they are general potential targets for engineering of high-yield microbial cell factories. Streptomyces, well-known producers of natural product pharmaceuticals, contain an abundance of sugar transporters, while few of them are well characterized and applied. Here, we report a previously unidentified ATP-binding cassette (ABC) sugar transporter TP6568 found within a Streptomyces avermitilis transposon library, along with its key regulator GM006564. Subsequent in silico molecular docking and genetic experiments demonstrated that TP6568 possessed a broad substrate specificity. It could not only promote uptake of diverse monosaccharides and disaccharides, but also enhance the utilization of industrial carbon sources such as starch, sucrose, and dextrin. Constitutive overexpression of TP6568 resulted in decrease of residual total sugar by 36.16%, 39.04%, 38.40%, and 30.21% in engineered S. avermitilis S0, Streptomyces caniferus NEAU6, Streptomyces bingchenggensis BC-101-4, and Streptomyces roseosporus NRRL 11379 than their individual parent strain, respectively. Production of avermectin B1a, guvermectin, and milbemycin A3/A4 increased by 75.61%, 56.89%, and 41.13%, respectively. We then overexpressed TP6568 in combination with the regulator GM006564 in a high-yield strain S. avermitilis S45, and further fine-tuning of their overexpression levels boosted production of avermectin B1a by 50.97% to 7.02g/L in the engineering strain. Our work demonstrates that TP6568 as a promising sugar transporter may have broad applications in construction of high-yield Streptomyces microbial cell factories for desirable natural product pharmaceuticals. KEY POINTS: • TP6568 from Streptomyces avermitilis was identified as a sugar transporter • TP6568 enhanced utilization of diverse industrially used sugars in Streptomyces • TP6568 is a useful transporter to construct high-yield Streptomyces cell factories.

Bio-hydrolysis Study of Lactose in Produced Yoghurt by β-Galactosidase from Lactobacillus fermentum

The present study investigated the physicochemical and biohydrolysis of lactose in conventional and locally produced yoghurt drinks, respectively. Physicochemical properties of the conventional yoghurt in the presence of the locally produced one were: pH 3.0; 4.0, titratable acid 1.14; 1.04, conductivity 2751.54, 2204, viscosity 71.11; 112.14, TDS 1788.5; 1433, TSS 781; 654, TS 3532.54; 2087, Mg 11.06; 34.19, Ca 28.76; 45.21, TOC 155.23; 145.23 and TOM 190.93, 178.63 for yoghurt sample I and II respectively. Lactose concentrations of the respective yoghurts were: 2.12 and 1.79 Mg/ml. β-galactosidase was produced from isolated Lactobacillus sp under submerged fermentation system after 12 days of incubation. 60% ammonium sulphate was found suitable for precipitation of proteins with highest enzyme activity, the precipitate was desalted through reverse osmosis using dialysis bag. Optimum biohydrolysis was achieved after 20 hours of incubation with residual sugar concentration of 0.51 mg/ml while the control experiment had 0.93 mg/ml of the residual sugar. Optimum pH and temperature of hydrolysis were: 5.0 and 70°C respectively. Rate of hydrolysis proceed linearly as the enzyme concentration increases from 0-20% v/v. the present study has shown exclusively the nutritional components of yoghurts drinks commercially sold in the market, it went further to show hope for the metabolic compromised individuals with intolerance to lactose as the enzyme lactase produced from non noscomial organism showed great potentials of hydrolysis.

Effect of Apple Cultivar and Selected Technological Treatments on the Quality of Apple Distillate.

Apple producers are looking for new markets to dispose of their harvest surpluses. One of the solutions may be the production of apple spirits by small distilleries. This study aimed to evaluate the influence of apple cultivars and technological treatments, i.e., pasteurization, depectinization, and deacidification, on the fermentation efficiency and quality of the distillates. Samples for fermentation were prepared from Polish apple cultivars (Antonówka, Delikates, Kosztela, Kronselska). The control samples were raw pulp-based samples. After fermentation, the samples were analyzed for ethanol, residual sugars, and by-product content by the HPLC technique. The distillates were tested for volatile compounds by the GC-MS method and their sensory evaluation was performed. Raw pulp-based samples, independent of the apple cultivar, showed fermentation efficiencies between (75.77 ± 4.69)% and (81.36 ± 4.69)% of the theoretical yield. Depectinization of apple pulp prior to fermentation resulted in the highest ethanol concentration and yield up to approximately 89%. All tested apple distillates were rich in volatile aroma compounds and met the requirements of the EU regulation for hydrogen cyanide content. The obtained results indicate that the tested apple cultivars can be used for the efficient production of apple spirits, providing producers with an opportunity for brand development.

Process of Bacterial Cellulose Production from Tofu Wastewater Without Pretreatment Using Acetobacter xylinum

Bacterial cellulose (BC) is an alternative cellulose source that warrants more investigation due to its limited efficiency and high production costs. This research aims to investigate the generation of bacterial cellulose from tofu wastewater using Acetobacter xylinum without pretreatment. The experiment was run on two media: tofu wastewater with and without additional sugar. The fermentation was run in a dark cabinet using a static batch method in numerous fermenter trays, each with a working volume of 1000 mL. Each experiment used 900 mL of tofu wastewater medium plus an extra 100 mL inoculum (equal to 10% v/v), which was then cultured at room temperature and harvested on days 6, 12, 18, 24, and 30. The weight of nata de soya, BC, and residual sugar were all measured from the samples. The results of the experiments revealed that the best incubation time was 18 days. The fermentation employing tofu wastewater medium with added sugar yielded nata de soya of 227.3 g/L and BC of 32.2 g/L, while the medium without added sugar yielded 103.9 g/L and BC of 9.3 g/L. The medium with added sugar yielded higher BC productivity, 1.79 g/L.day, compared to 0.57 g/L.day in the medium without added sugar. On the other hand, the BC results per sugar consumption were 0.62 g BC/g sugar and 0.36 g BC/g sugar, respectively, for the medium with and without added sugar.

Monitoring of Chemical and Fermentative Characteristics during Different Treatments of Grape Pomace Silage

Grape pomace is a fibrous food with satisfactory quantities of residual sugars. It meets the desirable characteristics for conservation in the form of silage for later use in animal feed, mainly for ruminant herbivores. Fresh grape pomace was subdivided into three treatment groups: grape pomace as a control, grape pomace treated with an inoculum of lactic acid bacteria, and grape pomace treated with zeolite. The treatments were performed in micro-silos over 90 days. There was a significant change (p < 0.05) in the chemical characteristics, content of biologically active compounds, and fermentative characteristics during the silage of all treatments. After 30, 60 and 90 days of ensiling, silages treated with inoculum and zeolite had better fermentation quality indicated by significantly (p < 0.05) lower pH and ammonia-nitrogen contents compared with those of the control. Also, the additives have decreased the total polyphenols and tannins for 97% in average which confirmed that lactic acid bacteria and zeolite positively effect on the degradation of polyphenols and tannins in grape pomace silage. The Flieg score was calculated and the values were above 80% what refers to excellent silage. In conclusion, our results suggest that inoculant and zeolite supplementation improves the quality of grape pomace silage for later use in animal feed.

Artificial neural network and genetic algorithm coupled fermentation kinetics to regulate L-lysine fermentation

Fermentation plays a pivotal role in the industrialization of bioproducts, yet there is a substantial lag in the fermentation process regulation. Here, an artificial neural network (ANN) and genetic algorithm (GA) coupled with fermentation kinetics were employed to establish an innovative lysine fermentation control. Firstly, the strategy of coupling GA with ANN was established. Secondly, specific lysine formation rate (qp), specific substrate consumption rate (qs), and specific cell growth rate (μ) were predicted and optimized by ANN-GA. The optimal ANN model adopts a three-layer feed-forward back-propagation structure (4:10:1). The optimal fermentation control parameters are obtained through GA. Finally, when the carbon to nitrogen ratio, residual sugar concentration, ammonia nitrogen concentration, and dissolved oxygen were [2.5, 4.5], [6.5, 9.5] g·L−1, [1.0, 2.0] g·L−1 and [20, 30] %, respectively, the lysine concentration reaches its peak at 213.0 ± 5.10 g·L−1. The novel control strategy holds significant potential for optimizing the fermentation of other bioproducts.

Effect of Yeast Concentration on Quality Parameters of Ber (Ziziphus mauritiana) Fruit (cv. Umran) Wine during Ageing

The present investigation was carried on for production of ber wine using yeast (Saccharomyces cerevisiae var. ellipsoideus) for fermentation. The quality parameters of ber wine were predicted by Design-Expert 7.7.0 software for optimizing the process parameters. The results obtained at T4 treatment (5 % inoculum) were encouraging with TSS (7.61 Brix), pH (4.06), residual reducing sugars (5.22 %) and alcohol (10.92 %) on 0th day of ageing with desirability factor of 0.95 followed by the results obtained on 90th day of ageing for T4 treatment (5 % inoculum) were TSS (6.27 °Brix), pH (4.22), residual reducing sugars (4.71 %) and alcohol content (12.07 %) with desirability factor of 0.93.

Growth of alfalfa in the presence of metabolites from a dark septate endophyte strain Alternaria sp. 17463 cultured with a non-ionic surfactant and emulsifier.

Dark septate endophytes (DSE) was widely used in the agriculture and ecological restoration. The objective of this work was to assess the effect of culture media non-ionic surfactant and emulsifier on the biomass and metabolites of DSE strain Alternaria sp. 17463. Changes in the composition of DSE metabolites following the addition of Tween 80 during liquid culture of a DSE fungus were analyzed and used in growth tests of alfalfa.Shaking flask fermentation was carried out and the surfactant was fed to the fungus during the fermentation. The residual sugar content and pH declined significantly in the medium and the biomass of DSE increased by 7.27% over controls with no surfactant. Metabolomics analysis showed that adding the surfactant significantly increased the content of 63 metabolites (P<0.05). These include lipids and lipid-like molecules, organooxygen compounds, amino acids and organic acids, and flavonoids. Enrichment analysis of metabolic pathways indicates that surfactant addition promoted carbohydrate metabolism and amino acid synthesis. A plant hydroponic experiment indicated that these changes in metabolites altered the root structure of alfalfa seedlings. They also promoted significant increases in root length and root surface area, and increased alfalfa total biomass by 50.2%. Addition of the surfactant promoted sugar utilization by the DSE fungus and increased the synthesis of lipids and amino acids, resulting in the ability of the fungal metabolites to change root structure and promote plant growth.

Degradation of acrylic-melamine based varnish containing Tinuvin 292 with accelerated exposure in fluorescent UV and condensation

This study explored the growth and fermentation capabilities of four distinct yeast strains, including Saccharomyces cerevisiae var. boulardii CNCM I-745, S. cerevisiae 7012, S. cerevisiae 7028, and S. cerevisiae var. diastaticus BE-134, with the aim of identifying the most suitable strain for the production of a fermented beverage from soybean residue hydrolysate (SRH). The results were as follows: S. cerevisiae 7012 exhibited the most efficient fermentation, with residual sugar content of 2.16 g/100 ml, an ethanol concentration of 1.39% v/v, and a favourable aroma, receiving a sensory score of 4.3/5 points. Within this sensory profile, the aromatic compound 2-phenylethanol was found to be the predominant component. Additionally, S. cerevisiae var. boulardii CNCM I-745 demonstrated superior biomass production ability, achieving a cell density of 7.71 log CFU/ml after 48 hours of fermentation solution also showed the highest antioxidant activity, equivalent to 1.63 mg of ascorbic acid per 100 ml. Consequently, these two yeast strains were selected for combined use in fermentation to leverage the probiotic characteristics of S. cerevisiae var. boulardii CNCM I-745 and the flavouring capacity of S. cerevisiae 7012 in creating fermented beverages from SRH.

Assessment of growth and fermentation of some yeasts on soybean residue hydrolysate

This study explored the growth and fermentation capabilities of four distinct yeast strains, including Saccharomyces cerevisiae var. boulardii CNCM I-745, S. cerevisiae 7012, S. cerevisiae 7028, and S. cerevisiae var. diastaticus BE-134, with the aim of identifying the most suitable strain for the production of a fermented beverage from soybean residue hydrolysate (SRH). The results were as follows: S. cerevisiae 7012 exhibited the most efficient fermentation, with residual sugar content of 2.16 g/100 ml, an ethanol concentration of 1.39% v/v, and a favourable aroma, receiving a sensory score of 4.3/5 points. Within this sensory profile, the aromatic compound 2-phenylethanol was found to be the predominant component. Additionally, S. cerevisiae var. boulardii CNCM I-745 demonstrated superior biomass production ability, achieving a cell density of 7.71 log CFU/ml after 48 hours of fermentation solution also showed the highest antioxidant activity, equivalent to 1.63 mg of ascorbic acid per 100 ml. Consequently, these two yeast strains were selected for combined use in fermentation to leverage the probiotic characteristics of S. cerevisiae var. boulardiiCNCM I-745 and the flavouring capacity of S. cerevisiae 7012 in creating fermented beverages from SRH.

Conversion of residual sugars from vinasses to 5-Hydroxymethyl furfural (5-HMF) and phenolic compounds using ion exchange resins and thermal treatment

Due to its physicochemical composition, the final disposal of vinasses denotes a severe environmental problem. This work passed vinasses at 2.4 and 7.0 pH through ion exchange Amberlite FPX66 and Dowex Optipore SD2 resins and two thermal treatments (130 °C, 40 min, and 0.5% H2O2). Furanic and phenolic compounds increased, and sugar removal was determined using UPLC, HPLC, and FTIR analysis. The highest increase for 5-HMF was found using SD2 resin to 7.0 pH vinasses and two thermal treatments (494.87 mg/L). The resins did not adsorb in the case of furfural. The highest increase in phenolic compounds was observed in 3-hydroxybenzoic (9.22 mg/L), vanillic (5.02 mg/L), syringic (1.68 mg/L), and 2,4-di-tert-butylphenol (1.23 mg/L). The highest values were found at pH 7.0 and after a second thermal treatment. The highest removal of sugars and Chemical Oxygen Demand (COD) occurred in FPX66 resin using vinasses to 2.4 pH and two thermal treatments, with 66.9 and 54%, respectively. Xylose was reduced between 74.5 and 88% with the SD2 in both pH and with two thermal treatments, and FPX66 resin with vinasses to 7.0 pH and two thermal treatments. At the same time, sucrose was removed 99.5% after the FPX66 resins with two treatments and 2.4 pH. Inulin is reported in this work for the first time in tequila vinasse (4530 mg/L). Using vinasses to obtain compounds of economic importance helps to valorize this residue.

Synergistic effect of residual sugar on freeze–thaw stability of high internal phase emulsions using glycosylated cod protein as interface stabilizer

Nowadays, glycosylated protein seems to be one of the most effective stabilizers for preparing freeze–thaw stabile emulsion; nevertheless, few papers mentioned the relationship between the residual free sugars after the glycosylation reaction and the freeze–thaw stability of high internal phase emulsions (HIPEs). Herein, glucose was used to prepare glycosylated cod proteins (GCPs). The synergistic effect was related to the grafting degree of GCP, and the amount of glucose added to prepare freeze–thaw stable HIPEs was reduced from 20% to 4% when the grafting degree of GCP increased from 0% to 31.58% (i.e. 12% GCP). This might be due to fewer ice crystals forming in water phase or less destruction of emulsion droplets by ice crystals. The obtained results in this study will allow developing freeze–thaw stable HIPEs or new frozen ingredients.

Construction of Novel Yeast Strains from Candida tropicalis KBKTI 10.5.1 and Saccharomyces cerevisiae DBY1 to Improve the Performance of Ethanol Production Using Lignocellulosic Hydrolysate.

Increased consumption of xylose-glucose and yeast tolerance to lignocellulosic hydrolysate are the keys to the success of second-generation bioethanol production. Candida tropicalis KBKTI 10.5.1 is a new isolated strain that has the ability to ferment xylose. In contrast to Saccharomyces cerevisiae DBY1 which only can produce ethanol from glucose fermentation. The research objective is the application of the genome shuffling method to increase the performance of ethanol production using lignocellulosic hydrolysate. Mutants were selected on xylose and glucose substrates separately and using random amplified polymorphic DNA (RAPD) analysis. The ethanol production using lignocellulosic hydrolysate by parents and mutants was evaluated using a batch fermentation system. Concentrations of ethanol, residual sugars, and by-products such as glycerol, lactate and acetate were measured using HPLC machine equipped with Hiplex H for carbohydrate column and a refraction index detector (RID). Ethanol produced by Fcs1 and Fcs4 mutants on acid hydrolysate increased by 26.58% and 24.17% from parent DBY1, by 14.94% and 21.84% from parent KBKTI 10.5.1. In contrast to the increase in ethanol production on alkaline hydrolysate, Fcs1 and Fcs4 mutants only experienced an increase in ethanol production by 1.35% from the parent KBKTI 10.5.1. Ethanol productivity by Fcs1 and Fcs4 mutants on acid hydrolysate reached 0.042 g/L/h and 0.044 g/L/h. The recombination of the genomes of different yeast species resulted in novel yeast strains that improved resistance performance and ethanol production on lignocellulosic hydrolysates.

Sweet Wine Production from the Side-Stream of Industrial Corinthian Currant Processing: Product Quality, Antioxidant Capacity, and Volatilome.

In the frame of efforts to add value to the Mediterranean currant cultivation and processing sectors, which is essential for their sustainability, sweet wine production is proposed from the finishing side-stream (FSS) of premium quality Corinthian currants, involving complete fermentation using an alcohol-tolerant yeast followed by (i) the addition of FSS to extract sugars or (ii) syrup made from FSS to adjust sweetness. Wine was also made by (iii) ceasing fermentation at the desired sugar level by ethanol addition. The non-fortified wines had 15.2-15.5% ethanol, 115-145 g/L residual sugar, 7.2-7.6 g/L titratable acidity, low volatile acidity (VA; <0.33 g/L), 280-330 mg/L phenolic content (TPC) (as gallic acid), and 23.8-35.6 mg/L antioxidant capacity (AC) (as ascorbic acid). In total, 160 volatiles were identified by SPME GC-MS, including compounds derived from the grapes, the raisin drying, and the fermentation process. The non-fortified wines had better characteristics (mainly VA, AC, and TPC) than the fortified wine, while sweetness adjustment by FSS is the simplest and lowest cost method since it does not involve ethanol or syrup addition. The proposed methods can lead to good quality sweet wines with a characteristic fruity (grape/raisin) flavor that could be commercialized as specialty raisin beverages or liqueurs.

Diversity of Indigenous Saccharomyces cerevisiae Yeast Strains in Cabernet Sauvignon Fermentations from Utiel-Requena Region (Spain) as a Resource to Improve Wine Distinctiveness

The aim of this study was to isolate and characterize autochthonous Saccharomyces cerevisiae yeasts from Cabernet Sauvignon grape must and to analyze how they impacted the final characteristics of the wines obtained from the same type of must. This work was carried out in a “Pago” winery located in Requena, Spain. Twenty-two isolates were obtained from grape must. After molecular identification and typing, 11 different strains were determined. Growth-related parameters and metabolic characteristics (glucose and fructose consumption and ethanol, glycerol and acetic acid production) were determined via laboratory-scale fermentations (50 mL) of Cabernet Sauvignon must. From 2 L fermentation batches, the residual sugar, density, ethanol concentration, titratable and volatile acidities, pH and polyphenolic and volatile compounds were determined, as well as the sensory attributes of the produced wines. Differences between strains in the growth and metabolic parameters were observed. Eleven S. cerevisiae strain profiles were characterized to establish which strain or strains of the selected yeasts would produce the highest polyphenolic and aromatic concentrations of the red Cabernet wines made in the “Pago winery”, to then multiply them for their use to make the red wines of this winery.

Study on the technology of kumquat grapefruit sour beer

A kumquat-grapefruit acid beer was brewed with Australian barley malt, lactobacillu, D17 yeast, Qingdao hop flower, kumquat concentrated juice and grapefruit concentrated juice as raw materials by using special mash and fermentation process. The effects of acidification degree, the addition amount of kumquat and grapefruit juice concentrate and the addition time on beer flavor were studied in this paper. The results showed that when the pH was adjusted to 3.5 by acidification, the sour beer produced by adding 6% kumquat concentrated juice and 4% grapefruit concentrated juice before the CO2 pressure of the tank rised, the beer has white and exquisite foam with prominent fruit aroma, especially those of kumquat and grapefruit. The beer body was clear and transparent, with about 5% residual sugar. The sweet and sour taste of the beer was balanced. The beer contained unique nutrients of kumquat and grapefruit also, and was especially suitable to drink for brewers and ladies.