Tpp

pyruvate decarboxylase ^ CO2

a-acetolactate/acetaldehyde-TPP

|CO2

CO2 diacetyl reductase diacetyl —^ ^ ► acetoin reductase / % "

NADH+H NAD

acetoin reductase c

NADH+H

NAD 2,3-butanediol catalyzed by a-acetolactate synthase and requiring high concentrations of pyruvate. The a-acetolactate is unstable in the presence of oxygen and is finally decarboxylated, nonenzy-matically, to form diacetyl. It is important to note that diacetyl is not necessarily the terminal end-product of the pathway. Further reduction of diacetyl can also occur, forming acetoin and 2,3-butanediol, compounds that contribute no flavor or aroma to the product.

Following the addition of the culture, the mix is incubated at 21°C to 22°C for twelve to sixteen hours. At the end of the fermentation, when the titratable acidity has reached 0.85% to 0.90% and the pH has decreased to about 4.5, the product is cooled to 2°C and agitated to break up the coagulum. Salt is usually added, and, if desired, butter granules or flakes are added. The finished product should be viscous and pourable.The product is pumped into containers and distributed.

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