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Issue 83 - Rising to the challenge

Whisky Magazine Issue 83
October 2009

 

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Rising to the challenge

Fermentation is a prime example of multi-tasking,with yeast having to grow,produce alcohol and create various flavours. So,how does yeast manage to tick all the boxes? Ian Wisniewski finds out challenge.

Wort is technically known as wash once yeast has been added, although this term generally applies to the fermented liquid. There are three critical stages during fermentation: the lag phase, exponential phase and stationary phase, which refer to the growth of the yeast, rather than the actual fermentation process.

“Immediately after pitching, the yeast adjusts to the wort and, during this time, there is a lull or ‘lag phase'before it starts to metabolise and use up the small amount of dissolved oxygen available in the wort,”says Grant MacKenzie of Kerry Ingredients and Flavours, a leading yeast supplier which is part of the Kerry Group.

Even before the end of the lag phase, which typically lasts several hours, the yeast experiences significant growth.

“By the time yeast goes into the exponential phase it may already have doubled in quantity,”says Dennis Watson of Chivas Brothers.

The first sugar on the menu for the yeast is glucose. This is the simplest and most easily digestible sugar within the wort, comprising one glucose unit.

“Yeast would be feeding on sugars before the lag phase ends, and as soon as yeast is digesting glucose it's producing alcohol.

Even before the washback is filled yeast starts to ferment the wort,” says Dennis Watson.

Working its way through glucose quite rapidly, yeast moves onto a more complex sugar, maltose, which comprises two glucose units linked together. As maltose is the main sugar in fermentation, yeast spends the longes...

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