ORGANIC – YEAST
Compressed Yeast (fresh or cake yeast) – compressed yeast is moist, perishable, and is preferred by professional bakers. The general rule is to use about twice the amount needed for dry active yeast.
Active Dry Yeast – is yeast that has been dehydrated and vacuumed packed. Because the drying process kills the outer layer of each granule, a quarter of the yield dies. These dead cell release glutathione, which has an unfavorable affect on the gluten in the flour. It must be rehydrated in 4 times its weight in water at about 110ºF (43ºC) before use. Bread bakers try and stay clear of this one because of the negative effects of the flavor.
Instant Yeast – does not need to be hydrated and can be added directly to the dough at the beginning of the mixing process.
SAF Yeast (Osmotolerant) – can withstand higher amounts of sugar and acidity that typically slow down regular yeast strains. SAF Gold is a brand that you can get your hands on.
Wild – yeast that is present in the air, on seeds, grains, flour and grape skins. Saccharomyces exiguous is the species most used in leavening starters for sourdough breads. To convert fresh yeast to dry:Amount of fresh yeast in the formula x 0.5 = amount of active dry yeast. To convert dry yeast to fresh yeast:Amount of dry yeast in the formula x 0.35 = amount of fresh yeast.
CHEMICAL LEAVENING AGENTS
Baking Soda: is the chemical sodium bicarbonate. If moisture and an acid are present, baking soda releases CO2, which leavens the product. Heat is not necessary for the reaction. For this reason they must be baked at once.
Baking Powder: are mixtures of baking soda plus an acid that reacts with it. It contains starch to prevent them from lumping and reduces the leavening power to a standard level Single-Acting: requires only moisture in order to be able to release gas to leaven the product. Double-Acting: releases some gas when it is cold, but requires heat to complete the reaction. If too much is used, undesirable flavors can be created, also, excess leavening may create an undesirable light, crumbly texture. Cakes may rise too much and then fall before they set.
Baking Ammonia: Is a chemical leavening agent made up of a mixture of ammonia carbonate and ammonia bicarbonate. It decomposes rapidly during baking to form CO2, ammonia gas, and water. Only heat and moisture are necessary for it to work. No acids are needed.
MECHANICAL LEAVENING AGENTS
Creaming: is the process of beating fat and sugar together to incorporate air. It is an important technique in cake and cookie making. Some pound cakes and cookies are leavened almost entirely by this method.|
Foaming: is the process of beating eggs, with or without sugar, to incorporate air. Foams made with whole eggs are used to leaven sponge cakes, while angel food cakes, meringues, and soufflés are leavened with egg whites.
Steam: When water turns to steam, it expands to 1,0000 times it original volume. Because all baked products contain some moisture, steam is an important leavening agent. Puff pastry, cream puffs, popovers, and piecrust are leavened primarily by steam. If the starting baking temperature is high, steam is produced rapidly and leavening is greater. One reason to begin cooking puff pastry at a higher temperature for the first 10 or 15 minutes then finish baking at a lower temperature to full cook the dough.
Just two sources for more information check out:
Harold McGee’s: On Food and Cooking – The Science and Lore of the Kitchen (2004, 884p) ISBN: 9780684800011
Wayne Gisslen: Professional Baking Fourth Edition (2005, 701p) ISBN: 9780471464273