Biology

Yeast: a single-celled
microorganism

Did you know that one cubic centimetre of fresh yeast, or about one gram, can contain up to 10 billion living yeast cells!

These cells are microscopic fungi: unlike other microorganisms such as bacteria or viruses, yeasts are eukaryotic cells.

This means that they have a clearly defined nucleus and the genetic material necessary for the biosynthesis of complex molecules such as enzymes, beta-glucans, mannoproteins, and lipids. 

Thanks to these precious molecules, yeast is able to ferment and transform matter into other useful substances.

Yeast: a nutritional treasure

Due to their nutritional richness, yeasts are also an excellent source of nutrients such as minerals, vitamins and amino acids that are vital for our health.

A dual metabolism: aerobic
and anaerobic

Yeasts have a flexible metabolism, so that they can live in both aerobic conditions, i.e. in the presence of oxygen, and anaerobic conditions, i.e. without oxygen.

In aerobic mode, yeasts have the optimal conditions to grow and multiply rapidly.

However, when they are deprived of oxygen, they turn to the surrounding matter, which they ferment and transform into carbon dioxide, alcohol and flavour compounds, thus making it possible to produce bread, wine, beer and other alcohols.

Aerobic conditions:
yeasts multiply and grow

In the presence of oxygen, yeast converts glucose into carbon dioxide (CO2) and water (H2O) while also producing a large amount of energy.
This is the metabolic process of respiration:
C6H12O6 + 2 02 > 2CO2 + 6H20 + 266 Kcal
The yeast cell uses the energy produced in this reaction to maintain its vital functions and reproduce.
This is the same process that is used in a yeast factory to grow yeast on a large scale. To multiply, yeast also needs other nutrients such as nitrogen, phosphate, vitamins and minerals.

Anaerobic conditions: yeasts start
an alcoholic fermentation process

Deprived of oxygen, yeasts do not grow but begin the metabolic process of fermentation, which consists of transforming glucose into alcohol (C2H50H), carbon dioxide (CO2), acids and flavour compounds, while releasing a much smaller amount of energy.
C6H12O6 -> 2C2H50H + 2C02 + Volatile Organic Compounds (VOCs) + small amount of energy
During fermentation, the small amount of energy released (20 times less than for respiration), reduces the yeast’s growth. On the other hand, it is this fermentation process that allows us to make bread, beer and wine… Yeasts are effectively miniature natural biochemical factories!

Below are the 2 metabolic pathways

Molasses is essential
to produce yeast

To provide the energy necessary for growth and multiplication, yeast needs a carbon source.

Consisting of 24% carbon, and containing almost 50% sugar, molasses is the main source of energy for the yeast. Other sugar syrups can also be used. They are co-products of sugar production from sugar beet (or sugar cane).
Did you know… It takes one ton of sugar beet to produce less than 40 kg of molasses!

In yeast production processes, various syrups and molasses are selected and mixed to make up the substrate that the yeast uses to multiply and grow. Molasses also contains minerals that are necessary for the yeast’s growth.

Molasses’ high nutritional value makes it suitable for yeast cultivation, for animal feed and as a food ingredient, e.g. in the production of the famous speculoos Belgian biscuits!

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