BEER VOLATILE COMPOUNDS IN DEPENDENCE ON YEAST STRAIN USED FOR FERMENTATION

Transcription

1 BEER VOLATILE COMPOUNDS IN DEPENDENCE ON YEAST STRAIN USED FOR FERMENTATION Daniela Šmogrovičová Department of Biochemical Technology Institute of Biotechnology and Food Science

2 Beer flavour Result of a complex combination of components malt, hops, water yeast metabolites by-products during fermentation and maturation make an important contribution to flavour 2

3 Yeast metabolites in beer The most notable metabolites are: ethanol and carbon dioxide a large number of other sensory active compounds diacetyl acetaldehyde higher alcohols esters 3

4 Yeast and flavour of beer Brewer s yeast bottom-fermenting top-fermenting Yeast strains their own character impart different aroma and flavour characteristics to beer may vary in which complex sugars they can ferment how high their alcohol tolerance is 4

5 Fermentation temperature and flavour of beer Bottom fermented beer fermentation at low temperatures Higher temperatures increase the rate of yeast metabolism and fermentation influence each biochemical reaction of yeast metabolism, changing the balance of flavour compounds Temperatures above 14 C results in a product with significantly poorer aroma and taste

6 The goal of this study To identify the factors that impact the formation of sensory active metabolites in beer Their role in sensory assessment The influence of yeast strain industrially used top-fermenting bottom-fermenting fermentation temperature wort gravity

7 Acetaldehyde Higher alcohols Studied compounds propanol, 1-butanol, 2-butanol, iso-butanol, 1-pentanol, 3- methyl-1-butanol (iso-amyl alcohol), hexanol Esters acetates methyl, ethyl, butyl, iso-butyl, iso-amyl, hexyl, 2-phenylethyl ethyl butyrate, ethyl iso-valerate, ethyl hexanoate, ethyl octanoate

8 Acetaldehyde the most important aldehyde of beer in beers usually lies in the range 2 20 mg/l at concentrations of mg/l acetaldehyde causes green apple flavour, green vegetation or vegetable flavour in levels over 150 mg/l may cause an aldehydic character of high astringency values

9 Acetaldehyde formation intermediate from carbohydrates to ethanol formation occurs during the first three days of fermentation permanent reduction during maturation and aging depends on yeast strain

10 Higher alcohols propanol and 2-methylpropanol (iso-butanol) rough flavours, harshness of beer butanol, 2-butanol alcoholic perception, general alcohol warming sensation in the mouth 2-methylbutanol (amyl alcohol) fruity flavour in threshold conc. of 50 mg/l 3-methylbutanol (iso-amyl alcohol) burning disagreeable odour in conc. higher than 1 mg/l pentanol (amyl alcohol) cough-exciting odour and burning taste hexanol odour of freshly mown grass phenylethanol sweet or rose flavour

11 Higher alcohols formation arises through decarboxylation and reduction of the appropriate -keto acid keto-acids are produced via catabolic or anabolic pathways, depending on the concentration of amino acids available either by transamination of an amino acid present in the medium (Ehrlich pathway) or from the anabolic pathway from pyruvate

12 Esters ethyl acetate fruity sweet, appr. 1/3 of all esters in beers methyl acetate glues, nail polish remover butyl, iso-butyl, iso-amyl, hexyl, 2-phenylethyl acetate fruity banana, apple, floral rose aromas ethyl isovalerate pleasant aroma, fruity flavour ethyl butyrate pineapple flavouring, fresh orange juice ethyl hexanoate, ethyl octanoate, ethyl decanoate apple

13 Esters formation can be formed by a simple condensation reaction between an alcohol and a carboxylic acid, although the rate of this reaction is too slow the condensation reaction between a higher alcohol and an activated acyl-coenzyme A (acyl-coa) catalysed by alcohol acyltransferases no direct relationship between yeast growth and ester synthesis

14 Higher alcohols-to-esters ratio the flavour of a beer depends not only on the content of its compounds but more on their ratio the optimum higher alcohols-toesters ratio for lagers according to literature is from 4.1 to 4.7:1

15 concentration (µg/l) Results Concentrations of the studied compounds were proportional to the wort gravity The exception was acetaldehyde its concentration in beers of gravity 10 P was similar than that in beers of gravity 12 P, or slightly higher 4 3 ethyl butyrate 2 1 pentanol acetaldehyde 0 10 P wort 12 P wort

16 concentration (µg/l) Results The maximum concentrations of the studied compounds were observed in top-fermented beers due to higher fermentation temperatures The exceptions were butanol, butyl acetate, ethyl iso-valerate and ethyl octanoate bottomfermenting yeasts topfermenting yeasts

17 Results Flavour-active compounds produced by two different bottom-fermenting yeast strains were noticeably different in the content of: ethyl acetate ethyl octanoate iso-amyl acetate In beers of gravity 10 P the most significant difference was in the iso-amyl and ethyl acetate content In beers of gravity 12 P, the most significant differences were observed in the ethyl octanoate production

18 concentration (µg/l) Differences in flavour-active compounds production by two bottom-fermenting yeast strains, wort gravity 10 P strain W34, wort 10 P strain 2, wort 10 P 0 18

19 concentration (µg/l) Differences in flavour-active compounds production by two bottom-fermenting yeast strains, wort gravity 12 P strain W34, wort 12 P 20 0 strain 2, wort 12 P 19

20 Aromatic profile of top fermented beers using different yeast strains alcohol alcohol pear banana pear banana apple pineapple apple pineapple strain I.S.C. 46, wort 10 P strain I.S.C. 46, wort 12 P strain I.S.C 57, wort 10 P strain I.S.C 57, wort 12 P 20

21 Aromatic profile of bottom fermented beers using different yeast strains alcohol alcohol pear banana pear banana apple pineapple apple pineapple strain 2, wort 10 P strain W34, wort 10 P strain 2, wort 12 P strain W34, wort 12 P

22 Conclusion The concentrations of the studied compounds were proportional to the wort gravity, the exception was acetaldehyde The maximum concentrations of the studied compounds were observed in top-fermented beers due to higher fermentation temperatures, with exceptions of ethyl iso-valerate, butyl acetate, butanol and ethyl octanoate Flavour-active compounds produced by two different industrially used yeast strains were noticeably different

23 Thank you for your attention!