BAKERY CHEMISTRY

We use a characteristic reaction of acids to make light, fluffy pancakes, waffles, cakes, biscuits, and other baked goodies. This useful reaction is the one that takes place between acids and bicarbonates.

Acid + metal bicarbonate ® salt + H₂O + CO₂

A leavening agent, used to make batters and doughs rise, works by generating carbon dioxide gas, which becomes distributed throughout the batter or dough in little bubbles. When these bubbles are heated during baking, they expand, and the batter or dough rises to give a light product. The baking powder called for in recipes contains the gas producing materials. In two popular brands of baking powder, the active ingredients are sodium bicarbonate, NaHCO₃, calcium hydrogen phosphate, CaHPO₄, and sodium aluminum sulphate, NaAl(SO₄)₂. Both the CaHPO4, and NaAl(SO₄)₂, behave as acids when they come in contact with water. The liberated H⁺ ions then react characteristically with the sodium bicarbonate. The net ionic reaction is

H⁺_(aq) + HCO₃^-_(aq) ® H₂O_(l) + CO_2(g)

The advantage of using baking powder is that it acts rapidly. A slower leavening process is used with most breads. Yeast, a living microorganism is added to the dough along with sugar. The Yeast slowly metabolizes the sugar and produces ethyl alcohol and carbon dioxide as products. The ethy1 alcohol evaporates as the bread bakes, and the CO₂ gas, which has been distributed throughout the dough by kneading, expands and causes the dough to rise.

Some recipes don't call for baking powder but include ingredients like baking soda and sour milk or buttermilk.

These ingredients do the same thing as baking powder. Baking soda is just good old sodium bicarbonate again, NaHCO₃, and sour milk or buttermilk contains lactic acid. Once again, the H⁺ ions produced by the acid react with the bicarbonate to give CO₂. Why do you suppose sodium bicarbonate is called baking soda?

Living yeast is the leavening for most breads.