Dough and batter ingredients: Yeasts and chemical leavenings

Leavenings Leavenings are the ingredients that fill doughs and batters with bubbles of gas This makes the amount of solid material in a given volume less, making the product less dense

Yeasts Louis Pasteur, 150 years ago, studied a particular class of fungus called yeast Yeasts undergo fermentation – a gas producing process

The Fungi Yeasts are a group of microscopic, single celled fungi, relatives to the mushroom Some cause infection, some cause food spoilage, and some are used in brewing and baking

Where did they come from? Yeasts were fist obtained from grain surface, supplied by an earlier piece of dough, or from the surface of beer brewing vats

Where are we now? Strains of yeast specifically for bread making are grown on molasses in industrial fermentation tanks

Yeast metabolism Yeasts metabolize sugars for energy and produce carbon dioxide and alcohol C6H12O6 2C2H5OH + 2CO2

Fermentation In making beer and wine, the carbon dioxide escapes leaving the alcohol behind With bread, the carbon dioxide and alcohol get trapped, then are expelled from the dough during baking

Using sugars in dough Yeasts grown on glucose, fructose, and maltose which enzymes in the flour produce from broken starch granules A small amount of sugar added will increase yeast activity, while a large amount will decrease it as does table salt

The importance of temperature Cells grow and produce gas most rapidly at around 94 degrees Fahrenheit Our challenge will be the cold temperatures in the kitchen