Simultaneous control of apparent extract and volatile compounds concentrations in low-malt beer fermentation

The Impact of Selected Lachancea Yeast Strains on the Production Process, Chemical Composition and Aroma Profiles of Beers

Changing trends in the brewing market show that breweries want to attract consumers with new products. New flavours and aromas in beer can be achieved by using various additives. However, non-Saccharomyces yeast strains make it possible to produce beer with an original sensory profile but according to a traditional recipe (without additives). The aim of this study was to evaluate the influence of 10 different yeast strains, belonging to the species Lachancea thermotolerans and L. fermentati, on the creation of different physico-chemical profiles in beers. For this purpose, the same malt wort with a 12°P extract, hopped with Octawia hops (8.4% alpha acids), was inoculated with the aforementioned yeast strains. The fermentation kinetics, the yeast's ability to ferment sugars, the production of organic acids and glycerol and the formation of volatile compounds in the beer were monitored. The beers obtained were classified as low-alcohol and regular. In addition, some beers were measured to have a low pH, qualifying them as "sour" beers, which are currently gaining in popularity. Most interesting, however, was the effect of the selected Lachancea yeast strains on the composition of the beer volatiles. In the second stage of this study, the beers obtained were again subjected to a chromatographic analysis, this time using an olfactometric detector (GC-O). This analysis was dictated by the need to verify the actual influence of the compounds determined (GC-MS) on the creation of the final aroma profile. This study showed that selected strains of Lachancea thermotolerans and L. fermentati have very high brewing potential to produce different original beers from the same hopped wort.

Methods for Estimating the Detection and Quantification Limits of Key Substances in Beer Maturation with Electronic Noses

To evaluate the suitability of an analytical instrument, essential figures of merit such as the limit of detection (LOD) and the limit of quantification (LOQ) can be employed. However, as the definitions k nown in the literature are mostly applicable to one signal per sample, estimating the LOD for substances with instruments yielding multidimensional results like electronic noses (eNoses) is still challenging. In this paper, we will compare and present different approaches to estimate the LOD for eNoses by employing commonly used multivariate data analysis and regression techniques, including principal component analysis (PCA), principal component regression (PCR), as well as partial least squares regression (PLSR). These methods could subsequently be used to assess the suitability of eNoses to help control and steer processes where volatiles are key process parameters. As a use case, we determined the LODs for key compounds involved in beer maturation, namely acetaldehyde, diacetyl, dimethyl sulfide, ethyl acetate, isobutanol, and 2-phenylethanol, and discussed the suitability of our eNose for that dertermination process. The results of the methods performed demonstrated differences of up to a factor of eight. For diacetyl, the LOD and the LOQ were sufficiently low to suggest potential for monitoring via eNose.

Identification and assessment of non-conventional yeasts in mixed fermentations for brewing bioflavored beer

The increasing demand for more flavored and complex beers encourages the investigation of novel and non-conventional yeasts with the ability to provide a combination of bioflavoring and low ethanol yields. The present study identified 22 yeasts isolated from different brewing sources, including the fermentation by-products known as yeast sludges, and characterized a selection of strains to find the more suitable for the aforementioned aims. HPLC and GC-FID analysis of its brewing products were performed. The most promising results were obtained with the non-conventional yeasts Pichia kudriavzevii MBELGA61 and Meyerozyma guilliermondii MUS122. The former, isolated from a Belgian wheat beer sludge, was capable of growing in wort (17.0°Bx., 20 °C) with very low ethanol yields (1.19 % v/v). Besides, upon mixed fermentations with Saccharomyces cerevisiae, was suitable to produce volatile compounds such as ethyl acetate, 2-phenyl ethanol and isoamyl alcohol, with characteristic fruity notes. M. guilliermondii MUS122, isolated from a golden ale beer sludge, partially attenuated the wort with low production of ethanol and biomass. In addition, provided some fruity and floral nuances to the aroma profile of mixed fermentations with brewer's yeast. The results suggest that these strains favor the development of more fruity-flowery aroma profiles in beers. Furthermore, they are suitable for use in mixed fermentations with Saccharomyces brewer's strains, although the ethanol level did not decrease significantly.

Evaluation of volatile compound profiles and sensory properties of dark and pale beers fermented by different strains of brewing yeast

To evaluate the differences in the volatile compound profile of dark and pale beers fermented by different strains of brewer's yeast, gas chromatography with flame ionization detection and gas chromatography mass spectrometry analysis of eight beers was carried out. The prevalent group of compounds in all the beers analysed were alcohols (56.41-72.17%), followed by esters (14.58-20.82%), aldehydes (8.35-20.52%), terpenes and terpenoids (1.22-6.57%) and ketones (0.42-1.00%). The dominant higher alcohols were 2-methylpropan-1-ol, 3-methylbutanol, phenethyl alcohol, among aldehydes furfural, decanal, nonanal, and among esters ethyl acetate, phenylethyl acetate and isoamyl acetate. Beers fermented by the top-fermenting yeast Saccharomyces cerevisiae var. diastaticus had the highest volatile content. The addition of dark malt in wort production process had no effect on the total content of volatiles, but for some beers it caused changes in the total content of esters, terpenes and terpenoids. Variations in the total volatile content between beers fermented by different yeast strains are mainly due to esters and alcohols identified. Sensory analysis of beers allowed us to identify the characteristics affected by the addition of dark speciality malts in the production of wort and yeast strains used in the fermentation process.

Pseudo-Lager—Brewing with Lutra® Kveik Yeast

Brewers commonly produce ales since the ale yeast is more resilient, ferments quicker and requires higher temperatures, which are easier to ensure as opposed to lager and pilsner, which require lower temperatures and longer lagering time. However, Kveik yeasts are also resilient, ferment at fairly high temperatures (up to 35 °C), and can provide light, lager-like beers, but more quickly, in shorter lagering time, and with reduced off flavors. Diacetyl rest is not needed. The intention of this paper was to assess the possibility of producing pseudo-lager by using Lutra® Kveik. A batch (120 L) was divided into six fermenting vessels and inoculated with Lutra® yeast. To test its possibility to result in lager-like beer at higher temperature, we conducted fermentation at two temperatures (21 and 35 °C). Fermentation subjected to 21 °C lasted for 9 days, while at 35 °C, fermentation was finished in 2 days. After fermentation, both beers were stored in cold temperatures (4 °C) and then kegged, carbonized, and analyzed (pH, ethanol, polyphenols, color, bitterness, clarity). Alongside the sensory evaluation, a GC-MS analysis was also conducted in order to determine if there are any difference between the samples.

Molecular profiling of beer wort fermentation diversity across natural Saccharomyces eubayanus isolates

The utilization of S. eubayanus has recently become a topic of interest due to the novel organoleptic properties imparted to beer. However, the utilization of S. eubayanus in brewing requires the comprehension of the mechanisms that underlie fermentative differences generated from its natural genetic variability. Here, we evaluated fermentation performance and volatile compound production in ten genetically distinct S. eubayanus strains in a brewing fermentative context. The evaluated strains showed a broad phenotypic spectrum, some of them exhibiting a high fermentation capacity and high levels of volatile esters and/or higher alcohols. Subsequently, we obtained molecular profiles by generating 'end-to-end' genome assemblies, as well as metabolome and transcriptome profiling of two Patagonian isolates exhibiting significant differences in beer aroma profiles. These strains showed clear differences in concentrations of intracellular metabolites, including amino acids, such as valine, leucine and isoleucine, likely impacting the production of 2-methylpropanol and 3-methylbutanol. These differences in the production of volatile compounds are attributed to gene expression variation, where the most profound differentiation is attributed to genes involved in assimilatory sulfate reduction, which in turn validates phenotypic differences in H2 S production. This study lays a solid foundation for future research to improve fermentation performance and select strains for new lager styles based on aroma and metabolic profiles.

Beer volatile compounds and their application to low-malt beer fermentation

Low-malt beers, in which the amount of wort is adjusted to less than two-thirds of that in regular beer, are popular in the Japanese market because the flavor of low-malt beer is similar to that of regular beer but the price lesser than that of regular beer. There are few published articles about low-malt beer. However, in the production process, there are many similarities between low-malt and regular beer, e.g., the yeast used in low-malt beer fermentation is the same as that used for regular beer. Furthermore, many investigations into regular beer are applicable to low-malt beer production. In this review, we focus on production of volatile compounds, and various studies that are applicable to regular and low-malt beer. In particular, information about metabolism of volatile compounds in yeast cells during fermentation, volatile compound measurement and estimation methods, and control of volatile compound production are discussed in this review, which concentrates on studies published in the last 5-6 years.

Physiological analysis of yeast cells by flow cytometry during serial-repitching of low-malt beer fermentation

At the end of beer brewing fermentation, yeast cells are collected and repitched for economical reasons. Although it is generally accepted that the physiological state of inoculated yeast cells affects their subsequent fermentation performance, the effect of serial-repitching on the physiological state of such yeast cells has not been well clarified. In this study, the fermentation performance of yeast cells during serial-repitching was investigated. After multiple repitchings, the specific growth rate and maximum optical density (OD(660)) decreased, and increases in isoamyl alcohol, which causes an undesirable flavor, and residual free amino acid nitrogen (FAN) concentrations were observed. The physiological state of individual cells before inoculation was characterized by flow cytometry using the fluorescent dyes dehydrorhodamine 123 (DHR) and bis-(1,3-dibutylbarbituric acid) trimethine oxonol (OXN). The fluorescence intensities of DHR, an indicator of reactive oxygen species (ROSs), and OXN, which indicates membrane potential, gradually increased as the number of serial-repitching cycles increased. Fluorescence intensity correlated strongly with cell growth. The subsequent fermentation performance can be predicted from this correlation.