Food or edible material: processes – compositions – and products – Fermentation processes – Alcoholic beverage production or treatment to result in...
Patent
1982-03-15
1987-11-24
Naff, David M.
Food or edible material: processes, compositions, and products
Fermentation processes
Alcoholic beverage production or treatment to result in...
426 13, 426 15, 426 16, 435174, C12C 1100, C12G 100, C12N 1116
Patent
active
047088753
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a process for producing fermented alcoholic products with a low diacetyl content by fermentation of a carbohydrate containing substrate with a microorganism.
When carbohydrate containing substrates, such as wort or grape juice, are fermented with yeast or other microorganisms, various processes take place in addition to the alcohol fermentation which may cause generation of undesired by-products. An example is the formation of diacetyl which has a strong and unpleasant smell even in very low concentrations.
Alcoholic beverages, such as beer or wine, may thus have an unacceptable aroma and flavour if the content of diacetyl considerably exceeds certain limits which, in the case of beer, is about 0.1 ppm.
Formation of diacetyl is also disadvantageous in the industrial production of ethanol because it is difficult to separate diacetyl from ethanol by distillation. A particular problem arises in the preparation of absolute ethanol where ethanol is dehydrated by azeotropic distillation with benzene. Diacetyl will accumulate in the benzene phase during the azeotropic distillation which may give rise to mixtures of diacetyl and benzene which makes it difficult to recover the benzene used for the azeotropic distillation.
The conventional brewing of beer comprises fermenting the wort with a suitable species of yeast, such as Saccharomyces cerevislae or Saccharomyces carlsbergensis.
The fermentation is usually effected in two steps, viz. a main fermentation of a duration of normally 7 to 10 days and a secondary fermentation--a so-called maturation process--which may take from 3 to 12 weeks. During the main fermentation most of the carbohydrates in the wort are converted to ethanol and carbon dioxide. Maturation is effected at a low temperature in the presence of a small residual amount of yeast. The purposes of the maturation are i.a. to precipitate undesirable, high molecular weight compounds and to convert diacetyl, 2,3-pentanedione, .alpha.-acetolactate and .alpha.-aceto-.alpha.-hydroxybutyrate to compounds, such as diols, which do not affect flavour and aroma. For example butanediol, the final product of the conversion of .alpha.-acetolactate and diacetyl in beer, does not affect flavour and aroma in concentrations below 500 mg per liter.
The enzymatic and chemical reactions important to the diacetyl content in beer is illustrated in the following scheme: ##STR1##
The precursor of diacetyl, .alpha.-acetolactate, is generated in the fermenting yeast by enzyme catalyzed condensation of pyruvate and the thiamine pyrophosphate of acetaldehyde and is an intermediate in the biosynthesis of the amino acid valine. .alpha.-Acetolactate may, however, also decompose spontaneously by oxidative decarboxylation to provide diacetyl [reaction (1)] which is subsequently reduced by reductases in the yeast cells, present during the beer maturation process. The decarboxylation of .alpha.-acetolactate is a temperature dependent reaction which proceeds relatively slowly at low temperatures, whereas the subsequent conversion of diacetyl to acetoin and 2,3-butanediol proceeds relatively fast, the consequence being that the rate determining step in removal of .alpha.-acetolactate and diacetyl from beer is the decarboxylation of the diacetyl precursor. Quite similarly, the rate determining step in removal of 2,3-pentanedione and .alpha.-aceto-.alpha.-hydroxy-butyrate is the spontaneous decarboxylation of the 2,3-pentanedione precursor.
To obtain maximum precipitation of high molecular weight substances and a beer of satisfactory quality, the maturation should take place at a temperature as low as possible, such as at about 0.degree. C. At this temperature it may take several months before the acetolactate has been completely removed and the resulting diacetyl has been reduced by the yeast. The maturation time may be reduced, however, if the process is allowed to proceed at higher temperatures, e.g. 1 or 2 weeks at 10.degree. C., 1 or 2 weeks at 5 C. and 1 or 2 weeks at -l.degree. C. Such a procedure will
REFERENCES:
patent: 3130055 (1964-04-01), Segel et al.
patent: 3733205 (1973-05-01), Shovers et al.
Amerine et al., The Technology of Wine Making 3rd, ed., The Avi Publishing Co. Inc., Westport, Conn. 1972 (pp. 284-287 & 204-207).
Loken, et al., Acetolactate Decarboxylase from Aerobacter aerogenes, Eur. J. Biochem. vol. 14, 1970 (pp. 133-137).
Juni, E., Mechanisms of Formation of Acetoin by Bacteria, Chemical Abstracts, 1953, 10053(d).
Hill, et al., Stereochemistry of Valine and Isoleucine Biosynthesis, Bioorganic Chemistry, vol. 8, 1979 (pp. 175-189).
Godtfredsen Sven E.
Larsen Bent A.
Ottesen Martin
De Forenede Bryggerier A/S
Naff David M.
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