HYDROPHOBIC POLYPEPTIDE EXTRACTION DURING HIGH GRAVITY MASHING— EXPERIMENTAL APPROACHES FOR ITS IMPROVEMENT

The aim was to establish if a substantial increase in hydrophobic polypeptides could be achieved during high gravity mashing. When worts with gravities ranging from 5–20°P were analysed for hydrophobic polypeptide content it was found that there was no appreciable increase in hydrophobic polypeptide levels. Remashing of the spent grains from low and high gravity mashes demonstrated that this resulted from inefficient extraction of hydrophobic polypeptide levels during the mashing process. For example, wort produced from remashed high gravity spent grains contained 150 mg/L hydrophobic polypeptides compared to only 10 mg/L in the low gravity remashed spent grains. Experiments were conducted, employing standard mashing techniques, in an attempt to increase the extraction of hydrophobic polypeptides during high gravity mashing. Thus the use of gypsum, proteolytic stands, varying liquor to grist ratios and wheat malt addition were all investigated for their effect on hydrophobic polypeptide extraction during high and low gravity mashing. Wort analysis demonstrated that none of the techniques employed had a significant effect on hydrophobic polypeptide extraction. When wort from remashed spent grains was used as mashing in liquor for a fresh mash and the resultant worts analysed for hydrophobic polypeptides it was observed that no increase in hydrophobic polypeptide extraction was achieved. For example, wort from the remashed high gravity spent grains, containing 140 mg/L hydrophobic polypeptides, when used as mashing-in liquor, produced no increase in hydrophobic polypeptide levels in the resultant high gravity wort (230 mg/L) when compared to a high gravity wort produced using distilled water as mashing-in liquor (255 mg/L). It is therefore concluded that a saturation point has been reached and no more hydrophobic polypeptides can be extracted during mashing regardless of the procedures employed.     

PITCHING RATE IN HIGH GRAVITY BREWING

The optimal pitching rate in high gravity worts (12–16°P) was about 0.3 g/l wet weight (2.3 × 10⁶ counted cells/ml) and per one percent of original wort gravity. In very high gravity worts (20–23°P) the corresponding figure was 0.4 g/l (2.9 × 10⁶ cells/ml). Higher amounts of yeast did not improve the fermentation rate. With increased original wort gravity, flocculation of the yeast weakened and the amount of cropped yeast decreased. The viability of the crop yeast was good. In the conditions used, excessive production of acetate esters occurred only with pitching rates lower than the recommended rate. As the original wort gravity increased, more fermentable extract was metabolized to ethanol rather than utilized for yeast growth. The highest ethanol yield obtained was 10.9% (v/v).     

STRAIN SPECIFIC RESPONSE OF BREWER'S YEAST STRAINS TO ZINC CONCENTRATIONS IN CONVENTIONAL AND HIGH GRAVITY WORTS*

The effect of zinc on a variety of yeast strains is extensively documented in the literature. However, due to the varied experimental protocols employed in each study there is little opportunity to directly compare the strain specificity of this ion. In the present study, the response of six yeast strains (three Saccharomyces cerevisiae (ale type) and three S.cerevisiae (lager type)) to altered zinc concentrations, in both high (1080 OG) and conventional (1048 OG) gravity worts, was investigated. Varying the initial wort zinc concentration in both gravities had an effect on the ethanol production, rate of fermentation, cell number and sugar uptake of all six strains studied. The extent of the response was found to be dependent upon the zinc concentration, the strain employed and wort gravity employed.     

The Loss of Hydrophobic Polypeptides during Fermentation and Conditioning of High Gravity and Low Gravity Brewed Beer

The object of this study was to investigate the loss of hydrophobic polypeptides, which are important for foam quality and stability in finished beer. Loss of hydrophobic polypeptide due to fermenter foaming occurs during transfer of fermented wort since a gradient of hydrophobic polypeptides towards the surface is created during fermentation. Due to higher polyphenol levels in high gravity (20°Plato) wort, more hydrophobic polypeptides are lost due to cold break (cold trub) precipitation compared to low gravity (12°Plato) wort. Another important factor affecting the loss of hydrophobic polypeptides could be proteinase A activity during fermentation, especially in high gravity fermentation where the yeast is exposed the higher stress. During high gravity fermentation, where osmotic pressures are higher, ethanol levels become greater, and nitrogen‐carbohydrate ratios are lower, more proteinase A is released by the yeast. This release of proteinase A into fermenting wort could have implications for the foam stability of the finished product.     

THE EFFECTS OF INCREASED MAGNESIUM AND CALCIUM CONCENTRATIONS ON YEAST FERMENTATION PERFORMANCE IN HIGH GRAVITY WORTS*

The response of e number of Saccharomyces cerevisiae (ale) and Saccharomyces uvarum (caris-bargenaia) (lager) strains to altered starting levels of magnesium and calcium in 12°P (1048 original gravity) or 20°P (1080 original gravity) wort were investigated. In general, the same trends were observed in all 6 strains, however the extent of the response to adjusted levels of magnesium and calcium were found to be strain dependent. The results indicate that an increased ratio of magnesium to calcium causes an increase in the initial fermentation rate, the rate and yield of ethanol produced and an increase in vitality at the end of fermentation, in all strains employed. Upon increasing the calcium to magnesium ratio it was found that the initial fermentation rate was decreased, resulting in an increased attenuation time in the case of the lager strains. It was also noted that increasing the calcium to magnesium ratio led to a decreased ethanol production, maltotriose uptake, and in the case of the lager strains, maltose uptake was also adversely affected under these conditions. Altering the calcium and magnesium levels had no effect on the viability of the yeast or on glycogen levels .