Microbes Move into Industry
Beyond the kitchen, microbes are put to work on a much larger scale to make products that are valuable to human beings, and beverages are one of the classic examples. Producing anything microbial in bulk means growing the organisms in very large vessels called fermentors (also spelt fermenters). A fermentor holds thousands of litres of medium, keeps the temperature and aeration under control, and lets a single useful microbe be multiplied into an industrial quantity of product.
This section looks at how one familiar microbe, yeast, is grown in such conditions to turn ordinary raw materials into alcoholic drinks.
Yeast, the Ancient Brewer
Yeasts, especially Saccharomyces cerevisiae, have been used from time immemorial to make beverages such as wine, beer, whisky, brandy and rum. This is the very same species used for bread-making, but when it is put to work on drinks it is commonly called brewer's yeast. So one organism wears two hats: baker's yeast when it raises dough, brewer's yeast when it ferments a broth.
The yeast is grown on malted cereals and fruit juices, and as it ferments these sugary raw materials it produces ethanol — the alcohol that all these drinks contain. It is the same alcoholic fermentation you have met before, now harnessed for industry.
Raw Material and Processing Decide the Drink
Why do we get so many different alcoholic drinks from essentially one microbe? The answer lies in two things: the type of raw material used for fermentation, and the type of processing the fermented broth is put through. Ferment grape juice one way and you get wine; ferment malted grain and process it differently and you get whisky.
The single most important processing distinction is whether the fermented broth is distilled or not. Distillation concentrates the alcohol by heating the broth and collecting the vapour, so the drink that results is much stronger than the broth itself.
With or Without Distillation
This is the key line to remember. Wine and beer are produced without distillation — the fermented liquid is consumed more or less as it comes from the fermentor, so these drinks have a relatively low alcohol content. Whisky, brandy and rum are produced by distillation of the fermented broth, which is why they are far more concentrated spirits.
So the same Saccharomyces cerevisiae, working on different raw materials and followed by different processing, gives the whole range of alcoholic beverages. The pattern is simple once you separate it out: same microbe, different feedstock, and distillation or no distillation.
Quick Recap
- Industrial-scale production of microbial products requires growing microbes in very large vessels called fermentors (fermenters).
- Yeasts, especially Saccharomyces cerevisiae — here called brewer's yeast, the same species used for bread — have been used since time immemorial for beverages.
- The yeast ferments malted cereals and fruit juices to produce ethanol (alcohol).
- The kind of drink depends on the raw material used and the type of processing (with or without distillation).
- Wine and beer are produced without distillation; whisky, brandy and rum are produced by distillation of the fermented broth.
Solved Examples — Section 3
Q1. Which microbe is used to produce alcoholic beverages, and what is it called in this context?
Answer: The yeast Saccharomyces cerevisiae — the same species used for bread-making, but here called brewer's yeast.
Q2. What raw materials does brewer's yeast ferment, and what does it produce?
Answer: It ferments malted cereals and fruit juices to produce ethanol (alcohol).
Q3. Which beverages are produced without distillation?
Answer: Wine and beer are produced without distillation.
Q4. Which beverages are produced by distillation of the fermented broth?
Answer: Whisky, brandy and rum are produced by distillation of the fermented broth.
Q5. What are fermentors, and why are they needed?
Answer: Fermentors are very large vessels in which microbes are grown; they are needed for producing microbial products, such as beverages, on an industrial scale.
Q6. Why can one yeast species give so many different alcoholic drinks?
Answer: Because the type of drink depends on the raw material used for fermentation and the type of processing (with or without distillation), not on using different microbes.