Humans have been baking raised bread for 6,000 years, but the nature of fermentation processes became clear only 150 years ago, after the research and inventions of Louis Pasteur, the biologist.
Yeast belongs to the group of microscopic, single-celled fungi. Of the more than a hundred species, some of which cause infectious diseases, some - causes food spoilage, there is a group of fungi used both in baking and in brewing beer.
You will find three types of baking yeast on the store shelves:
1. Wet or pressed yeast - this is a cube of live yeast. It is taken directly from fermentation tanks and packaged. Its cells are alive and produce more deacidifying gas than other species of yeast, although they are perishable and can be stored in the refrigerator for only 1-2 weeks. Pressed yeast gives a very soft texture and sweet taste to baked goods. It is pre-activated in warm water, or mixed directly into the dough.
2. Active dry yeast was invented in the 1920s. After removal from the fermentation tanks, the yeast is dried and packed in granular format. It is stored for months at room temperature. Fungi cells in dry yeast are dormant, to activate it needs to be placed in warm water at 41-43 degrees, with a little sugar. After a few minutes the yeast will be activated, which means that the volume will double and the mass will foam, only then is it added to the flour or dough.
3. Instant dry yeast is an innovation of the 1970s. It absorbs liquid faster than active dry yeast and therefore does not require pre-activation - it directly mixes with the flour and is kneaded. If you read in the recipe to prepare dough by mixing yeast with flour, you should definitely use instant dry yeast.