Inverkan av vörtens valinhalt på mängden diacetyl som produceras under jäsningen av öl

Diacetyl and 2,3-pentanedione are butter-tasting vicinal diketones produced as by-products of valine and isoleucine biosynthesis during wort fermentation, and their presence in beer is usually unwanted. Yeast are able to reduce diacetyl and 2,3-pentanedione into compounds with higher flavour thresholds, and this is usually achieved during a resource-and time-consuming maturation phase after the primary fermentation. One promising method of decreasing diacetyl production during fermentation is through the control of the valine content of the wort, since valine is involved with the feedback inhibition of enzymes controlling the valine biosynthesis pathway and indirectly the formation of diacetyl precursors. The objective of this thesis was to investigate the influence of valine supplementation, wort amino acid profile and free amino nitrogen content on diacetyl formation during wort fermentation with the lager yeast Saccharomyces pastorianus, by carrying out a series of small-scale (2-litre) and medium-scale (10-litre) fermentations, which were sampled and analysed for diacetyl and amino acid concentrations, along with standard beer parameters. Supplementation of valine to the wort resulted in decreased maximum (up to 37% lower) and final (up to 33% lower) diacetyl concentrations in all trials, and the composition of the amino acid spectrum of the wort also had an impact on diacetyl and 2,3-pentanedione production during fermentation. The results suggest that there is no correlation between the concentrations of wort amino acids and diacetyl production per se, but rather a negative correlation between the uptake rate of valine (and also other branched-chain amino acids) and diacetyl production was found. The results from all four experiments agree that fermentation performance and yeast growth was not affected by the studied levels of amino acid supplementations, implying that supplementation of valine or other amino acids will not affect the fermentation time nor the attenuation level achieved. Supplementation of amino acids did however have a minor effect on the concentrations of higher alcohols and esters linked to the amino acids via the Ehrlich pathway, suggesting that large levels of supplementation could affect the flavour profile of the beer. It can be concluded that modifying the amino acid profile of wort, especially in respect to valine and the other branched-chain amino acids, is an effective way of decreasing the amount of diacetyl formed during fermentation. This knowledge can be utilized for decreasing the maturation time of beer, however further research is required before it becomes feasible at an industrial scale

A Unique Saccharomyces cerevisiae × Saccharomyces uvarum Hybrid Isolated From Norwegian Farmhouse Beer: Characterization and Reconstruction

An unknown interspecies Saccharomyces hybrid, “Muri,” was recently isolated from a “kveik” culture, a traditional Norwegian farmhouse brewing yeast culture (Preiss et al., 2018). Here we used whole genome sequencing to reveal the strain as an allodiploid Saccharomyces cerevisiae × Saccharomyces uvarum hybrid. Phylogenetic analysis of its sub-genomes revealed that the S. cerevisiae and S. uvarum parent strains of Muri appear to be most closely related to English ale and Central European cider and wine strains, respectively. We then performed phenotypic analysis on a number of brewing-relevant traits in a range of S. cerevisiae, S. uvarum and hybrid strains closely related to the Muri hybrid. The Muri strain possesses a range of industrially desirable phenotypic properties, including broad temperature tolerance, good ethanol tolerance, and efficient carbohydrate use, therefore making it an interesting candidate for not only brewing applications, but potentially various other industrial fermentations, such as biofuel production and distilling. We identified the two S. cerevisiae and S. uvarum strains that were genetically and phenotypically most similar to the Muri hybrid, and then attempted to reconstruct the Muri hybrid by generating de novo interspecific hybrids between these two strains. The de novo hybrids were compared with the original Muri hybrid, and many appeared phenotypically more similar to Muri than either of the parent strains. This study introduces a novel approach to studying hybrid strains and strain development by combining genomic and phenotypic analysis to identify closely related parent strains for construction of de novo hybrids

Traditional Norwegian Kveik Are a Genetically Distinct Group of Domesticated Saccharomyces cerevisiae Brewing Yeasts

The widespread production of fermented food and beverages has resulted in the domestication of Saccharomyces cerevisiae yeasts specifically adapted to beer production. While there is evidence beer yeast domestication was accelerated by industrialization of beer, there also exists a farmhouse brewing culture in western Norway which has passed down yeasts referred to as kveik for generations. This practice has resulted in ale yeasts which are typically highly flocculant, phenolic off flavor negative (POF-), and exhibit a high rate of fermentation, similar to previously characterized lineages of domesticated yeast. Additionally, kveik yeasts are reportedly high-temperature tolerant, likely due to the traditional practice of pitching yeast into warm (>28°C) wort. Here, we characterize kveik yeasts from 9 different Norwegian sources via PCR fingerprinting, whole genome sequencing of selected strains, phenotypic screens, and lab-scale fermentations. Phylogenetic analysis suggests that kveik yeasts form a distinct group among beer yeasts. Additionally, we identify a novel POF- loss-of-function mutation, as well as SNPs and CNVs potentially relevant to the thermotolerance, high ethanol tolerance, and high fermentation rate phenotypes of kveik strains. We also identify domestication markers related to flocculation in kveik. Taken together, the results suggest that Norwegian kveik yeasts are a genetically distinct group of domesticated beer yeasts with properties highly relevant to the brewing sector

Lachancea fermentati strains isolated from Kombucha: fundamental insights, and practical application in low alcohol beer brewing

With a growing interest in non-alcoholic and low alcohol beer (NABLAB), researchers are looking into non-conventional yeasts to harness their special metabolic traits for their production. One of the investigated species is Lachancea fermentati, which possesses the uncommon ability to produce significant amounts of lactic acid during alcoholic fermentation, resulting in the accumulation of lactic acid while exhibiting reduced ethanol production. In this study, four Lachancea fermentati strains isolated from individual kombucha cultures were investigated. Whole genome sequencing was performed, and the strains were characterized for important brewing characteristics (e.g., sugar utilization) and sensitivities toward stress factors. A screening in wort extract was performed to elucidate strain-dependent differences, followed by fermentation optimization to enhance lactic acid production. Finally, a low alcohol beer was produced at 60 L pilot-scale. The genomes of the kombucha isolates were diverse and could be separated into two phylogenetic groups, which were related to their geographical origin. Compared to a Saccharomyces cerevisiae brewersâ yeast, the strainsâ sensitivities to alcohol and acidic conditions were low, while their sensitivities toward osmotic stress were higher. In the screening, lactic acid production showed significant, strain-dependent differences. Fermentation optimization by means of response surface methodology (RSM) revealed an increased lactic acid production at a low pitching rate, high fermentation temperature, and high extract content. It was shown that a high initial glucose concentration led to the highest lactic acid production (max. 18.0 mM). The data indicated that simultaneous lactic acid production and ethanol production occurred as long as glucose was present. When glucose was depleted and/or lactic acid concentrations were high, the production shifted toward the ethanol pathway as the sole pathway. A low alcohol beer (<1.3% ABV) was produced at 60 L pilot-scale by means of stopped fermentation. The beer exhibited a balanced ratio of sweetness from residual sugars and acidity from the lactic acid produced (13.6 mM). However, due to the stopped fermentation, high levels of diacetyl were present, which could necessitate further process intervention to reduce concentrations to acceptable levels

Anàlisi “shift share” de l’evolució del cens de porcí a Espanya (1962-2005)

El desenvolupament de la ramaderia intensiva s’ha produït mitjançant aglomeracions espacials de les explotacions ramaderes. El sector porcí és un dels principals exponents d’aquesta aglomeració i concentració espacial. Per això s'ha realitzat el present PFC amb l'objectiu d'estudiar el procés de concentració de la producció porcina a les diferents Comunitats Autònomes entre els anys 1962 i 2005, investigant els efectes diferencials i d’assignació de l’anàlisi “shift share”. Es conclou que en els anys estudiats hi ha hagut dos pols d'aglomeració de la cabana porcina, Catalunya+Osca i la Regió de Múrcia, que han estat cabdals en l'abastiment dels mercats