All about Yeast
What is Yeast? Is it an animal, vegetable or mineral?
Yeast is classified as a fungus, a single-cell organism related to mushrooms, and it floats in the air all around us. Wild yeast spores are constantly floating in the air and landing on uncovered foods and liquids. No one's sure when these wild spores first interacted with foods but it's known that the Egyptians used yeast as a Leavening agent more than 5,000 years ago. some historians believe that the action of yeast was probably noticed when bread dough was acidentally forgotten and left too long before baking and the lighter, fluffer bread that resulted became very popular.
Back in the time of Chaucer, the action of yeast in ale was so mysterious that the foam was simply called 'godisgoode', because it's powers were perceived to be a miracle. The truth would have to wait until the mid-19th century and the discoveries of one Louis Pasteur who proved that yeast is alive.
Scientists have identified over 600 species of yeast since then, although some experts believe that these species discovered so far may only represent 1% of the total varieties of yeast!
Yeast is a living ,microscopic single-cell organism that, as it grows, converts its food (through a process known as fermentation) into alcohol and carbon dioxide. This trait is what endears years to winemakers, brew makers and bread bakers. In the making of wine and beer, the yeast's manufacture of alcohol is desired and necessary for the final product; and carbon dioxide is what makes beer and champagne effervescent.
The art of bread making needs the carbon dioxide produced by yeast in order for dough to rise. To multiply and grow, all yeast needs is the right environment, which includes moisture, food (in the form of sugar or starch) and a warm, nuturing temperature (15oC to 25oC is best).
There are two types of yeast that are commercially available:
Baker's yeast is categorised into two basic types - active dry yeast and compressed fresh yeast.
Active dry yeast is the form of tiny, dehydrated granules which is what we will use today. these yeast cells are alive but dormant befuase of the lack of moisture. when mixed with a warm liquid (35oC to 42oC), the cells once again become active.
Compressed fresh yeast comes in tiny (0.06 ounce), square cakes, is moist and extremely perishable. It must be refrigerated and used within a week or two, or by the date indicated on the package. It can be frozen, but should be defrosted at room temperature and used immediately.
Yeast breathes air just like us and it exhales carbon dioxide just like us. When introudced to dough or batter containing gluten (when wheat flour is mixed with water), the yeast blows bubbles that leaven the dough, producing a desirable texture. The word yeast, in fact, derives from the Greek word zein (to boil), which is understandable considering all the bubbles healthy yeast can blow.
Yeast eats and just like a lot of people, commercial yeast prefers sugar to flour. That is why yeast needs assistance from a specail enzyme (added to most flours by the miller) in order to digest the nourishment in starch. since it eats, yeast also has to poo! Unappetizing as that sounds, we need yeast waste because it tcontains various flavour compounds as well as alcohol, which evaporates during baking, contributing considerably to a proper "oven spring" - the critical transition from dough to bread.
Yeast reproduces when it is well fed and comfortable; new yeast cells pop out of the side of old ones. This means that if conditons are right, one single yeast can become the centre of a large clump of yeast cells in a short amount of time.