#603 1869 · Eben Norton Horsford (Rumford Chemical Works) · Food chemistry / baking
Acid and base leavening powder reacted the moment they touched, so Horsford didn't separate them — he removed what was setting them off
the problem
A packaged leavening powder's two active ingredients reacted before bakers could use it
background
Through the 1800s, bread relied on yeast for leavening, but yeast was a living organism whose potency varied unpredictably batch to batch. Chemists found in the 1840s that cream of tartar mixed with baking soda released carbon dioxide gas far more predictably, but cream of tartar was a byproduct of European winemaking that American bakers had to import at real expense — Harvard chemist Eben Horsford set out in 1854 to find a domestic substitute, and by 1856 had patented monocalcium phosphate, made from treated animal bone, as a cheaper acid replacement.
The obstacle wasn't the chemistry, it was the packaging. Monocalcium phosphate (the acid) and sodium bicarbonate (the base) start reacting and releasing their leavening gas the moment they're combined in the presence of moisture, including ordinary ambient humidity. The standard practical fix was to sell the two ingredients in separate packages and have the baker measure and combine them fresh at the moment of use, which kept the chemistry safe but pushed the work, and the risk of getting proportions wrong, onto every individual baker.
what everyone would do
The chemistry Horsford needed was already known by the 1850s: an acid and a base, combined with water, release carbon dioxide gas predictably. The obstacle was that the same reaction which makes good leavening also happens the moment ambient moisture reaches the two ingredients sitting together in one container — so the standard practical fix was to package the acid and the base separately and have the baker measure and combine them fresh right before baking, which kept the chemistry safe but pushed the work, and the risk of getting the proportions wrong, onto every individual baker.
what they saw
Horsford saw that the two reactive ingredients didn't actually need to be kept apart in space if the thing that triggered their reaction, moisture, could be kept away from them instead. Adding cornstarch as a desiccant meant the acid and base could sit together in the same sealed can, inert, because the starch absorbed whatever ambient humidity would otherwise have set off the reaction early — the reaction was suppressed at its actual trigger rather than prevented by physical separation.
the move
In 1869, Horsford added cornstarch to the mixture — not as a leavening ingredient itself, but as a desiccant that absorbs ambient moisture and keeps the acid and base dry enough that they don't react with each other inside a sealed can. That let Rumford Chemical Works pre-mix the correct proportions of all three ingredients at the factory and ship a single, ready-to-use product, rather than requiring bakers to combine two separately packaged chemicals themselves.
why it works
Because the cornstarch kept both ingredients dry enough to remain unreactive during storage and shipping, the factory could pre-mix an exact, tested ratio of acid to base once, at scale, rather than leaving that measurement to every individual baker working from two separate packages. That is what made the product genuinely reliable — the same reaction happened the same way every time a home baker added water, because the proportions were fixed at the factory instead of eyeballed in a kitchen, which is exactly the predictability that let baking powder replace both cream of tartar and yeast as the standard leavening agent.
the payoff
Because the cornstarch buffer suppressed the premature reaction rather than trying to keep the reactive ingredients apart in separate containers, every can shipped with a predictable, factory-controlled ratio of active ingredients — bakers using the same amount of baking powder got the same rising action every time, something neither unpredictable yeast nor a baker's own hand-mixed acid-and-base combination could reliably guarantee. Modern baking powder became Rumford's primary product.
where it breaks
This only works when you can actually identify and control the specific trigger — here, moisture — that sets off the unwanted premature reaction; if the reactive ingredients could be set off by something harder to exclude or buffer against, packaging them together would remain unsafe no matter how they were combined. It also depends on the buffering agent being inert enough not to interfere with the product's intended function once the reaction is finally triggered on purpose — cornstarch does nothing to disrupt the leavening reaction itself when water is finally added, which is what makes it a buffer rather than just another ingredient competing with the reaction.
what came after
The formula Horsford developed in 1869 — an acid, a base and a starch buffer, combined in one package — is essentially unchanged in the baking powder sold today, and the American Chemical Society designated it a National Historic Chemical Landmark in 2006.
references
- [1]A Colorful History of Baking Powder (And Its Unlikely Inventor)The MIT Press Reader (excerpt from "Born in Cambridge: 400 Years of Ideas and Innovators"), 2021thereader.mitpress.mit.edu
- [2]Rumford Baking PowderInvention & Technology Magazine, 2006inventionandtech.com