Quick breads are breads made with chemical leaveners, instead of yeast. They’re quick in that they don’t have to ferment.
Chemical leaveners are interesting concoctions. They were originally byproducts of salt-making. Most salt is made by boiling or slowly evaporating a brine. This brine could be seawater, or it could be water that was flushed through an underground deposit to dissolve the salt and ease its extraction. Either way, once the brine is reduced to a certain concentration, sodium chloride, table salt, precipitates and is easily harvested. The remaining liquid, called bittern, is still rich in all kinds of other compounds: Epsom salt, for instance, and magnesium. In 1792 sodium carbonate, or soda, was extracted from bittern for the first time, and subsequently used in countless industries, including the manufacture of chemical leaveners.
Baking Soda. Most are familiar with baking soda, sodium bicarbonate. It’s a basic (high pH) powder, and when mixed with an acid, like vinegar, it produces carbon dioxide gas and water. The carbon dioxide is what makes it useful as a leavener. Quick breads leavened by soda therefore require some form of acid in the batter, like buttermilk or sour cream.
Baking Powder. Baking powder works on the same principle: the mixing of an acid and a base to produce carbon dioxide and water. The main difference is that the acid and base are both present in baking powder, but they can’t interact with each other until they’re mixed into a liquid or semi-liquid batter. The base is sodium bicarbonate. There are several acid salts that can be used. My can of Magic Baking Powder tells me it uses monocalcium phosphate. There is also usually some kind of neutral starch, like cornstarch. You can actually make baking powder at home by combining baking soda and cream of tartar (an acid salt, originally a byproduct of wine production) in a ratio of 1:2 by volume.
Double-acting baking powder provides two rises for quick breads. The first occurs as soon as the wet and dry ingredients are combined, as described above. The second rise happens in the oven, and is driven by an acid that only reacts with bases at those elevated temperatures.
The most common way to make quick breads is to combine all the dry ingredients (flours, sugars, salt, leaveners) in one bowl, all the wet ingredients (dairy, eggs, oils) in another, then to pour the wet into the dry. The batter is mixed until the wet and dry are just, just combined, as over-mixing will develop too much gluten. Some recipes even specify that there should be little clumps of unincorporated dry ingredients. Because of the lack of extensive mixing, quick breads have a tender, slightly crumbly texture, compared to lean, yeasted breads like baguette. The absence of yeast also gives them a “cleaner,” less complex flavour.
1. Kurlansky, Mark. Salt: A World History. ©2002 Mark Kurlansky. Vintage Canada 2002 Edition. Page 297.