Rubber Biscuit

The main thing that differentiates a biscuit from a cracker is its ability to rise. And of course that doesn’t happen by itself. It takes a little chemical mojo, and in our case that mojo comes from baking powder.

As I mentioned in one of last week’s posts, baking powder was the invention of one Alfred Bird, British pharmacist, experimental chemist and water glass-playing bon vivant. He was the one who first conceived of combining powdered sodium bicarbonate with potassium bitartrate (an acid salt also known as cream of tartar) to create a chemical leavener. Put the two chemicals together in the presence of water and the result is fizz, or more correctly, carbon dioxide bubbles. Dispersed through dough or batter, those bubbles become the basis of leavening, as they heat, fill with steam, and expand. It was Alfred Bird’s wife’s delicate digestion that was the prime mover behind the invention, as she was allergic to yeast and couldn’t eat conventional breads.

The idea wasn’t completely new. Bicarbonate of soda (baking soda) was in common use as a leavener for decades before. But soda, being an alkalai, needs an acid to react with, so home bakers were forced to improvise by adding acid substances to their batters and doughs, things like clabber (sour milk), vinegar, molasses, buttermilk, or citrus juices. But by pre-packaging soda with an acid salt (and a little cornstarch to prevent the two from reacting with any moisture present in the air), an all-in-one leavener was created. The only problem was that cream of tartar was expensive, so not everyone could afford the innovation. Eventually cream of tartar was replaced by a cheaper salt, calcium phosphate, which made it more commonly available. But the baking powder we know today wasn’t created until 1885 when another acid salt, sodium aluminum sulphate, was added to the mix. Like calcium phosphate, this compound also created bubbles in the presence of soda and water, but only at high temperatures. This improvement not only created more bubbles, it spread the reaction out over a longer period of time, eliminating the risk of all the carbon dioxide bubbling out before the bread or biscuits could be put in the oven. Because it offered two actions instead of one, the product was dubbed double acting baking powder. It has since become the standard chemical rising agent for bakers the world over.

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