The different presentations of baker’s yeast can be shown in their order of appearance during the manufacturing process :
Until 1825 when compressed yeast was introduced by Tebbenhof, yeast was sold in liquid form. The return to this form is a response to requests from industrial bakers.
This is the most widely used form in industrialized countries for economic and practical reasons. It comes in compact blocks which reduce contact with oxygen in the air. Its colour and crumbliness differ from one country to the other. The packaging of " wax paper " or " sulphide paper and cellophane " reduces gas transfer and controls moisture migration, to provide extended shelf life.
This comes in relatively fine and free flowing particles; it can thus be weighed or metered automatically. It is packed in multilayered paper bags which are polyethylene lined and sealed to prevent access of air.
Crumbled yeast is often dispersed into water by industrial bakers, which makes automatic dosage possible.
Active Dry Yeast
This yeast is dried in granular form or small beads. It is packed in tins, plastic bags or drums or sachets under vacuum. It is also available for domestic use in sachets of 5 to 11 g. It can be stored at ambient temperature.
The product hardiness gives a good level of stability making it popular in parts of the world where climatic conditions are less than ideal (high temperature and humidity).
This type of yeast has to be rehydrated in lukewarm water before use.
Instant Dry Yeast
The fine particles of instant dry yeast are vacuum-packed in sachets. It also exists in sachets of 10 g under protective atmosphere for domestic use. This type of yeast can therefore be stored at ambient temperature.
The instant dry yeast owes its name to the fact that it does not require prior rehydration before being added to flour. It may be used just as easily as compressed yeast.
Dry yeast with reducing power (Active form)
In granular form, packed in tins, this yeast is designed for pizza makers. Its moderate, regular gassing power provides the fermentation tolerance required for this type of application. Its reducing power makes it easy to shape the pizza thus avoiding the shrinkage effect.
This yeast is stripped of all its fermenting power. In the dough, the membranes (rendered completely permeable) allow the leakage of the whole cell content to pass through. One of its components, glutathione, has a reducing effect on the gluten.
This is reflected in :
improving the machinability of stiff doughs or those which have reached a high level of maturation;
accelerating the dough development during mixing which requires a decrease in mixing time by 15 to 20%. This characteristic reduces dough oxidation during mixing, therefore preserving the ferment flavour which gives aromatic quality to the finished product.