Production of yeasts

Ripening yeasts, like lactic acid bacteria, are also produced in specialised fermentors under strict hygiene conditions but with different nutrient sources and growth parameters. Notably, yeast fermentation needs to be conducted under aerobic (with oxygen or air) conditions. They are concentrated and mainly available as freeze-dried powders.

The baker’s yeast is commercially produced on a nutrient source which is rich in sugar (usually molasses: by product of the sugar refining). The fermentation is conducted in large tanks. Once the yeast fills the tank, it is harvested by centrifugation, giving an off-white liquid known as cream yeast. This is further processed into any of several different forms:

Compressed yeast: still widely used commercially, it is a soft beige solid block with  limited storage properties.

Active dry yeast: dried yeast presented in granules or beads that needs to be rehydrated before it can be used.

Instant yeast: vacuum packed fine powder that has become popular in home breadmaking, as it is easy to use