Mead production: Fermentative performance of yeasts entrapped in different concentrations of alginate

Mead is an alcoholic drink known since ancient times, produced by yeast fermenting diluted honey. However, the production of mead has suffered in recent years, partially owing to the lack of scientific progress in this field. In this study, two strains of Saccharomyces cerevisiae, QA23 and ICVD47, were immobilized in 2 or 4% (w/v) alginate beads to assess the most effective alginate concentration for yeast immobilization to produce mead. Neither of the alginate concentrations was able to prevent cell leakage from the beads. The fermentation length was 120h for both yeast strains. In all cases, at the end of the fermentation, the number of cells entrapped in the beads was higher than the number of free cells, and the total 4% alginate bead wet weight was significantly higher than the 2% alginate bead wet weight. In addition, the evaluation of mead quality showed that the yeast strain had significantly more influence on the physicochemical characteristics than the alginate concentration. Although the yeasts immobilized in the two alginate concentrations were able to perform the fermentation, further research is needed in order to understand the evolution of the yeast population inside the beads throughout the fermentative process.The research presented in this paper was partially funded by the Fundação para a Ciência e Tecnologia, and by the PTDC project (contract PTDC/AGR-ALI/68284/2006). A.P.P. is the recipient of a PhD grant from FCT (SFRH/BD/45820/2008).info:eu-repo/semantics/publishedVersio

Impact of inoculum size on mead aroma compounds formation by wine strains of S. cerevisiae

Mead is a traditional drink, containing 8-18% (v/v) of ethanol, which results from the alcoholic fermentation of diluted honey performed by yeasts. It has been reported that mead fermentation is a time-consuming process, and an important objective of mead makers is to reduce the fermentation time without decreasing the quality of the end product. A significant time can be saved in the fermentation process by increasing the pitching rate, i.e., the amount of suspended yeast cells added to a batch fermenter. However, an increase in the inoculum size could also have deleterious side effects on the flavour profile of the final beverage. Therefore, the aim of this study was to investigate the impact of the inoculum size of two commercial winemaking strains of Saccharomyces cerevisiae (Lalvin QA23 and Lalvin ICV D47) on the mead volatile aromatic compound production. Honey must was prepared according to the recipe developed by our team, supplemented with potassium tartrate, pH adjusted to 3.7 with malic acid and the nitrogen concentration adjusted to 267 mg/L with diammonium phosphate. The appropriate amounts of inoculum were pitched into the honey-must to obtain five different pitching rates. Mead produced was analysed for major volatile compounds by GC-FID and for minor volatile compounds by GC-MS. A total of twenty-seven fermentative aroma compounds including alcohols, esters, volatile phenols, volatile fatty acids and carbonyl compounds were identified and quantified in meads. It was observed quantitative differences in aroma profiles, confirming the contribution of both yeast strain and inoculum size on the sensory characteristics of meads. Of the twenty-seven volatile compounds quantified, fourteen could contribute to mead aroma and flavour because their concentrations rose above their respective thresholds. In general, the formation of these compounds was particularly pronounced at low pitching rates. The esters ethyl hexanoate, ethyl octanoate and isoamyl acetate were the most powerful odorants detected in all meads. In addition to this quantitative analysis of the impact of strain selection and inoculum size on mead aroma, a complementary sensorial evaluation of the meads would yield further useful information for mead producers

Effect of Saccharomyces cerevisiae cells immobilisation on mead production

Mead is a traditional alcoholic beverage obtained by the fermentation of diluted honey performed by yeasts. In this work the potential of application of immobilised yeast cells on single-layer Ca-alginate or double-layer alginateechitosan for mead production was assessed for the first time. The meads produced either with entrapped or free cells were evaluated in terms of quality and aroma profile. The immobilisation procedure had no adverse effect on cell viability, since minor differences were found in fermentation kinetics among the strains and immobilisation systems. The double-layer alginate-chitosan had no advantage compared with the single-layer Ca-alginate, as the number of free cells in the medium, resulting from cell leakage, was similar. Although meads obtained with entrapped yeast cells presented less ethanol and glycerol and more acetic acid, it exhibited larger amounts of volatile compounds. Immobilised cells produced meads with more compounds with fruity characteristics, such as ethyl octanoate and ethyl hexanoate; however the concentrations of undesirable compounds in such meads were also higher. The effect of immobilisation on the aroma profile was important, but the strain contribution was also of major importance. Thus, the sensory analysis of final product gives an important insight on the overall quality.The research presented in this paper was partially funded by the Fundacdo para a Ciencia e Tecnologia, (FCT) and by PTDC projects (contracts PTDC/AGR-ALI/68284/2006). A.P.P. is a recipient of a Ph.D. grant from the FCT (SFRH/BD/45820/2008)

Effect of nitrogen supplementation on yeast fermentation performance and mead quality

Mead is a traditional drink, containing X-1 X% (v/v) of ethanol, which results from the alcoholic fermentation of diluted honey performed by yeasts. However, when it is produced in a homemade way mead producers find several problems, namely, the lack of uniformity in the final products low or premature fermentations arrest, and the production of "off-flavours" by the yeasts. These problems could be due to several factors, including lack of essential nutrients such as a deficiency in available nitrogen. Additionally , it has been reported that mead fermentation is a time-consuming process, often taking several months to complete. depending on the type of honey, yeast strain anti honey-must composition. Since mead production is a time-consuming process. to make its production viable it is necessary to reduce the fermentation time while producing an end product of quality. Thus. the aim of this study was to evaluate I he effect of nitrogen addition 10 honey-must on two active dry wine yeasts (ADWY) fermentation performance, as well as on the mead composition and volatile aroma compounds production

Isolation of yeast strains with ability to reduce volatile acidity of wines

The objective of the present study was to isolate and characterize wine yeasts able to reduce volatile acidity of wines. From a set of 135 yeast isolated during a refermentation wine procedure, four strains revealed ability to use glucose and acetic acid simultaneously. The strains were tested regarding their growth patterns in a differential medium containing glucose (0.2% w/v) and acetic acid (0.5% v/v), at pH 4.0 or 6.0. The selected strains displayed growth associated to color change of the pH indicator of the medium indicative of simultaneous glucose and acetic acid consumption. Three of them were identified as Saccharomyces cerevisiae and one as Lachancea thermotolerans by sequencing the D1/D2 domain of the large subunit (26S) ribosomal DNA. In two culture media containing acidic wines with high glucose/low ethanol or low glucose/high ethanol concentrations, the S. cerevisiae strains showed an initial simultaneous consumption pattern of glucose and acetic acid under both aerobic and limited aerobic conditions, independently of the relative amounts of glucose and ethanol. This results show a high physiological diversity among strains of this species, validating our approach to search for interesting strains among indigenous yeasts. Comparatively, the isolated L. thermotolerans 44C and Zygosaccharomyces bailii ISA1307 were able to exhaust acetic acid only when grown under aerobic conditions. The S. cerevisiae strains characterized in the present study appear promising for the decrease of volatile acidity in acidic wines under the low-oxygen conditions of a typical refermentation process.Fundação para a Ciência e a Tecnologia (FCT) - programme POCI 2010 (project POCI/AGR/56102/2004)

Isolation and characterization of yeast strains with ability to decrease volatile acidity of wines

The level of acetic acid, the main component of volatile acidity, is critical for wine quality. Its concentration in wines is approximately 0.5 g/L and, legally, must remain below 1.0g/L. Winemakers use a procedure called “remostagem” to lower acetic acid of wines with high volatile acidity (above 0.8g/L). The spoiled wine is mixed with freshly crushed grapes (1) in a proportion of no more than 20-30% (v/v). The volatile acidity of this mixture and of the newly made wine should not exceed 0.6 and 0.3 g/L, respectively. The aim of this study is to select wine yeasts capable of decreasing the volatile acidity of spoiled wines. First, from 135 isolates colleted during a “remostagem” procedure, 4 wild yeasts were selected based on their ability to consume acetic acid in the presence of glucose at pH 4,0 or 6,0. The 4 strains were further analyzed regarding simultaneous acetic acid and glucose consumption, specific growth rate and ethanol production in comparison to the commercial strain Lalvin QA23, Saccharomyces cerevisiae IGC 4072 and Zygosaccharomyces bailii ISA 1307, using minimal media containing acetic acid (0.5%, v/v) and glucose (0.5%, w/v) at 25ºC and pH 3,0. Although less efficiently than Z. bailii the 4 isolated strains were able to use acetic acid in the presence of glucose. Their potential application in the deacidification of acidic wines is being studied.Programa Operacional Ciência e Inovação (POCI) 2010 - (FEDER/FCT, POCTI/AGR/56102/2004)

Isolation of yeast strains with ability to reduce volatile acidity of wines

The objective of the present study was to isolate and characterize wine yeasts able to reduce volatile acidity of wines. From a set of 135 yeast isolated during a refermentation wine procedure, four strains revealed ability to use glucose and acetic acid simultaneously. The strains were tested regarding their growth patterns in a differential medium containing glucose (0.2% w/v) and acetic acid (0.5% v/v), at pH 4.0 or 6.0. The selected strains displayed growth associated to color change of the pH indicator of the medium indicative of simultaneous glucose and acetic acid consumption. Three of them were identified as Saccharomyces cerevisiae and one as Lachancea thermotolerans by sequencing the D1/D2 domain of the large subunit (26S) ribosomal DNA. In two culture media containing acidic wines with high glucose/low ethanol or low glucose/high ethanol concentrations, the S. cerevisiae strains showed an initial simultaneous consumption pattern of glucose and acetic acid under both aerobic and limited aerobic conditions, independently of the relative amounts of glucose and ethanol. This results show a high physiological diversity among strains of this species, validating our approach to search for interesting strains among indigenous yeasts. Comparatively, the isolated L. thermotolerans 44C and Zygosaccharomyces bailii ISA1307 were able to exhaust acetic acid only when grown under aerobic conditions. The S. cerevisiae strains characterized in the present study appear promising for the decrease of volatile acidity in acidic wines under the low-oxygen conditions of a typical refermentation process.This study was supported by the programme POCI 2010 (project POCI/AGR/56102/2004

The effect of micro-oxygenation and cell immobilization on the reduction of excessive volatile acidity from wines

In our former studies we isolated and characterized wine yeasts with the ability to reduce volatile acidity of wines during a refermentation process, hich consists in mixing the acidic wine with freshly crushed grapes or musts or, alternatively, in incubating with the residual marc. Herein, we aimed to evaluate the effect of micro-oxygenation on the ability of previously selected S. cerevisiae strains to decrease volatile acidity from spoiled wines, and on possible changes in the wine aroma during such a refermentation processes. Both refermentation processes were carried out at a pilot scale (30 l), with an acidic wine with 2.80 gl−1 acetic acid and applying micro-oxygenation (20 mg.l- 1.h-1 of O2). Our data show that oxygen availability is not a key parameter for glucose and acetic acid consumption, but increased the final biomass for both commercial yeast strains tested. Volatile acidity of the final wines decreased to 0.38 gl-1 up to 0.68 gl-1, depending on the strain used. Combining analytical data (SPME coupled to GC-MS) with the sensorial analysis performed by a trained panel of 5 judges, the wines treated with micro-oxygenation revealed a vegetable character and mouth hardness in comparison to the more floral notes that predominated in wines obtained without micro-oxygenation. Currently, the efficiency of volatile acidity removal by S. cerevisiae S26 entrapped cells in one layer alginate beads or in double layer alginate – chitosan beads is being evaluated. The results indicate that removal is dependent on the initial cell concentration in the beads which showed to be important for bead stability and prevention of cell leakage

Effects of acetic acid, ethanol and SO2 on the removal of volatile acidity from acidic wines by two Saccharomyces cerevisiae commercial strains

Herein we report the influence of different combinations of initial concentration of acetic acid and ethanol on the removal of acetic acid from acidic wines by two commercial Saccharomyces cerevisiae strains S26 and S29. Both strains reduced the volatile acidity of an acidic wine (1.0 g l-1 acetic acid and 11% (v/v) ethanol) by 78% and 48%, respectively. Acetic acid removal by both strains was associated with a decrease in ethanol concentration of about 0.7 – 1.2% (v/v). Strain S26 revealed better removal efficiency due to its higher tolerance to stress factors imposed by acidic wines. We also demonstrate that the strong anti-oxidant and antiseptic effect of sulphur dioxide (SO2) concentrations up to 170 mg l-1 inhibit the ability of both strains to reduce the volatile acidity of an acidic wine under our experimental conditions. Therefore, deacidification should be carried out either in wines stabilized by filtration or in wines with SO2 concentrations below 75 mg l-1. Deacidification of wines with the better performing strain S26 was associated with changes in the concentration of volatile compounds. The most pronounced increase was observed for isoamyl acetate (banana) and ethyl hexanoate (apple, pineapple), with an 18- and 25-fold increment, respectively, to values above the detection threshold. The acetaldehyde concentration of the deacidified wine was 2.3 times higher, and may have a detrimental effect on the wine aroma. In addition, deacidification led to increased fatty acids concentration, but still within the range of values described for spontaneous fermentations, and with apparently no negative impact on the organoleptical properties. We propose the use of S. cerevisiae strain S26 for the efficient reduction of the volatile acidity from acidic wines with acetic acid and ethanol concentrations not higher than 1.0 g l-1 and 11% (v/v), respectively.Fundação para a Ciência e Tecnologi