A recent paper on fermentability:
Impact of dark specialty malts on extract composition and wort fermentation
Author(s): Coghe, S (Coghe, S); D'Hollander, W (D'Hollander, W); Verachtert, H (Verachtert, H); Delvaux, FR (Delvaux, FR)
Source: JOURNAL OF THE INSTITUTE OF BREWING Volume: 111 Issue: 1 Pages: 51-60 Published: 2005
Abstract: Dark specialty malts are important ingredients for the production of several beer styles. These malts not only impart colour, flavour and antioxidative activity to wort and beer, they also affect the course of wort fermentations and the production of flavour-active yeast metabolites. The application of considerable levels of dark malt was found to lower the attenuation, mainly as a result of lower levels of fermentable sugars and amino acids in dark wort samples. In fact, from the darkest caramel malts and from roasted malts, practically no fermentable material can be hydrolysed by pilsner malt enzymes during mashing. Compared to wort brewed with 50% pilsner malt and 50% dark caramel malt or roasted malt, wort brewed with 100% pilsner malt contained nearly twice as much fermentable sugars and amino acids. Reduced levels of yeast nutrients also lowered the fermentation rate, ranging from 1.7 degrees P/day for the reference pilsner wort of 9 EBC to 1.1 degrees P/day for the darkest wort (890 EBC units), brewed with 50% roasted malt. This additionally indicates that lower attenuation values for dark wort are partially due to the inhibitory effects of Maillard compounds on yeast metabolism. The application of dark caramel or roasted malts further led to elevated levels of the vicinal diketones diacetyl and 2,3-pentane-dione. Only large levels of roasted malt gave rise to two significant diacetyl peaks during fermentation. The level of ethyl acetate in beer was inversely related to colour, whereas the level of isoamyl acetate appeared to be affected by the use of roasted malt. With large levels of this malt type, negligible isoamyl acetate was generated during fermentation.
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Two papers that cited the above paper. I get a hoot out of the title
of the second one:
Population Size Drives Industrial Saccharomyces cerevisiae Alcoholic Fermentation and Is under Genetic Control
Author(s): Albertin, W (Albertin, Warren)2,3; Marullo, P (Marullo, Philippe)3,4; Aigle, M (Aigle, Michel)5; Dillmann, C (Dillmann, Christine)1; de Vienne, D (de Vienne, Dominique)1; Bely, M (Bely, Marina)3; Sicard, D (Sicard, Delphine)1
Source: APPLIED AND ENVIRONMENTAL MICROBIOLOGY Volume: 77 Issue: 8 Pages: 2772-2784 DOI: 10.1128/AEM.02547-10 Published: APR 2011
Abstract: Alcoholic fermentation (AF) conducted by Saccharomyces cerevisiae has been exploited for millennia in three important human food processes: beer and wine production and bread leavening. Most of the efforts to understand and improve AF have been made separately for each process, with strains that are supposedly well adapted. In this work, we propose a first comparison of yeast AFs in three synthetic media mimicking the dough/wort/grape must found in baking, brewing, and wine making. The fermentative behaviors of nine food-processing strains were evaluated in these media, at the cellular, populational, and biotechnological levels. A large variation in the measured traits was observed, with medium effects usually being greater than the strain effects. The results suggest that human selection targeted the ability to complete fermentation for wine strains and trehalose content for beer strains. Apart from these features, the food origin of the strains did not significantly affect AF, suggesting that an improvement program for a specific food processing industry could exploit the variability of strains used in other industries. Glucose utilization was analyzed, revealing plastic but also genetic variation in fermentation products and indicating that artificial selection could be used to modify the production of glycerol, acetate, etc. The major result was that the overall maximum CO(2) production rate (V(max)) was not related to the maximum CO(2) production rate per cell. Instead, a highly significant correlation between V(max) and the maximum population size was observed in all three media, indicating that human selection targeted the efficiency of cellular reproduction rather than metabolic efficiency. This result opens the way to new strategies for yeast improvement.
Instrumental measurement of beer taste attributes using an electronic tongue
Author(s): Rudnitskaya, A (Rudnitskaya, Alisa)1,2; Polshin, E (Polshin, Evgeny)2,3; Kirsanov, D (Kirsanov, Dmitry)2; Lammertyn, J (Lammertyn, Jeroen)3; Nicolai, B (Nicolai, Bart)3; Saison, D (Saison, Daan)4; Delvaux, FR (Delvaux, Freddy R.)4; Delvaux, F (Delvaux, Filip)4; Legin, A (Legin, Andrey)2
Source: ANALYTICA CHIMICA ACTA Volume: 646 Issue: 1-2 Pages: 111-118 DOI: 10.1016/j.aca.2009.05.008 Published: JUL 30 2009
Abstract: The present study deals with the evaluation of the electronic tongue multisensor system as an analytical tool for the rapid assessment of taste and flavour of beer. Fifty samples of Belgian and Dutch beers of different types (lager beers. ales, wheat beers, etc.), which were characterized with respect to the sensory properties, were measured using the electronic tongue (ET) based on potentiometric chemical sensors developed in Laboratory of Chemical Sensors of St. Petersburg University. The analysis of the sensory data and the calculation of the compromise average scores was made using STATIS. The beer samples were discriminated using both sensory panel and ET data based on PCA, and both data sets were compared using Canonical Correlation Analysis. The ET data were related to the sensory beer attributes using Partial Least Square regression for each attribute separately. Validation was done based on a test set comprising one-third of all samples. The ET was capable of predicting with good precision 20 sensory attributes of beer including such as bitter, sweet, sour, fruity, caramel, artificial, burnt, intensity and body.
Ray
