Monitoring the Growth of Yeast

715 Words3 Pages
Monitoring the Growth of Yeast

Introduction

Yeast is a microscopic fungus, of which there are hundreds of species.

It is extremely important brewing ingredient because different strains

give different beer types their distinctive and characteristic

flavors. When a brewery has found an ideal yeast, it will be retained

for many years. However, fresh batches are produced regularly from

samples kept under special laboratory conditions to prevent the built

up of microbiological contamination. (Just as milk can go sour – yeast

and bacteria can also contaminate beer). Individual yeast cells are

invisible to the naked eye, and are carried in air current. When they

grow on a suitable food source (for example fruit, such as grapes and

plums) they form ‘colonies’ of cells. (These can be seen as a fine

white powdery film on the skins of the fruit). Yeast can feed on a

variety of sugars, converting them into energy in order to grow and

multiply. When it first grows, the yeast cells need a supply of oxygen

in the same way a animals do when they convert sugar into the carbon

dioxide and energy. If animals run out of energy they die. But in the

absence of oxygen, yeast obtains its energy from ‘anaerobic

fermentation’ in which sugars are converted to alcohol and carbon

dioxide. Most importantly for the brewery, yeast produces a variety of

flavoring components (through side reactions), which help give the

beer its characters flavors. Also use top-fermenting yeast strains

that typically ferment between 65-75F and lagers use bottom fermenting

yeast stains that typically ferment 50-55F. Pitching temperature

should always be 80F or under because yeast will die if exposed to

temperature over 110F. Too high of a fermentation temperature or

higher alcohols (fusel alcohols). Yeast fermentation time will vary

depending on strain, temperature, and fermentations environment,

however most fermentations should be complete within 7-14 days.

Equipment and Materials

3 conical flaks

3 delivery tubes

Spatula

Balances

Fridge

Ammonium Sulphate (0.5)

Yeast powder (1g)
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