I was living in Chicago in the 90’s, first in Hyde Park (home of the wonderful Seminary Coop Bookstore and 57th Street Books) and, later, in Printer’s Row, which is just south of the Chicago Loop. As it was nearly Thanksgiving and I was living 1000 miles from my family (in Boston) at the time, I was pleased to receive a Thanksgiving Day invitation to (relatively) nearby Champaign-Urbana. I had been to Champaign a few times before and, well, there it is. At any rate, I gratefully accepted the invitation of the hostess and I volunteered to bake banana bread for the occasion. How hard can it be? I’m a chemist, after all. Since this was weeks before Thanksgiving, I felt I had ample time to get the job done. Over the next few days, I researched banana bread recipes and converged on a consensus recipe and made a shopping list as I did so. Here was my list:
Very ripe bananas
Some of these items I had on hand, but some I did not so, about a week before Thanksgiving, I went to the grocery store with my list and acquired the necessary ingredients. I was most concerned with the quality of the bananas as that is, after all, the key ingredient. That said, a week would be more than enough time to bring the bananas to the “ready” state. I had everything well in hand.
OK, now fast-forward a little bit to, um, 11:45 PM on the eve of Thanksgiving, and you find me in my kitchen, looking over the recipe, which read “put flour, baking powder, and baking soda in a bowl.” Baking soda? That wasn’t on my list! What am I supposed to do now? I should note that, at this point in the story, most people, knowing that I am a chemist guessed [incorrectly] that I went to the lab to get some baking soda. Baking soda is just a chemical and whether you buy it in the grocery store or from the Aldrich Chemical Company, it’s the same powdery white, odorless salt that dissolves instantly in water. It sounds a lot like iocane powder which, you may recall, was a critical element (though not an element) in The Princess Bride.
So I looked around my apartment and asked myself, “OK, what is the purpose of baking soda in baking?” Baking soda is only sodium bicarbonate, NaHCO3. It’s weakly acidic and weakly basic at the same time. When it reacts with acid, it makes carbonic acid, H2CO3, which rapidly decomposes to form carbon dioxide, CO2, and water, H2O.
You can see this in action if you dissolve a tablespoon of baking soda in about ½ cup of water and pour in a few tablespoons of vinegar (the active ingredient in vinegar is acetic acid and, in stores, you can by about a 3% solution – not very concentrated, so won’t hurt you, but it has a strong odor). You’ll see a gentle bubbling. You might want to try this in a sink. And it wouldn’t hurt to put on a pair of safety glasses – sunglasses would work too - so that you don’t splash any vinegar in your eyes. But even if you do, flush with water and you’ll be fine. Want more bubbles? Add vinegar directly to a tablespoon of baking soda in a glass. Try a little at first, just to see what you’re getting yourself into…
So the point of this excursion is to remind/show you that the purpose of baking soda is to generate CO2, which makes the bread rise. Baking powder actually contains a little bit of baking soda too – I didn’t know this at the time – as well as cream of tartar (derived from tartaric acid, which is found in wine as well as bananas), the purpose of which is to release a little acid and, in turn, CO2. But let’s return to my banana bread story.
So, by now it’s Midnight and I am driving to Champaign in 10 hours. By this time I had been thinking about the purpose of the baking soda and noticed, in my medicine cabinet a bottle of, wait for it, Tums! OK, so Tums doesn’t have baking soda in it. Rather, the active ingredient in Tums is magnesium carbonate, MgCO3, but it still reacts with acid and makes CO2 (don’t believe me? Pulverize a pellet and add some vinegar to it…). So, I took a single, mint-flavored, Tums and crushed it with the back of a spoon in a sturdy mug (I didn’t have, and still don’t, a mortar and pestle in my kitchen – it would have been really handy… my birthday is in October, by the way) and added it to the mix. I continued with the recipe, baked the banana bread, and drove down to Champaign for a Thanksgiving dinner that couldn’t be beat. The banana bread looked and tasted like the real thing and nobody was the wiser. Some time later, I confessed to the hostess who graciously replied, “I guess the Tums helped to settle our stomachs after eating so much turkey.” Thanks, Jeanne.
I have since made banana bread by the “standard” recipe but, a few years ago, I did a side-by-side comparison of Tums vs. baking soda. In a quality-control experiment conducted by students in Haverford College Chem 101b, the banana bread baked with baking soda rose noticeably higher, but was otherwise (and taste-wise) indistinguishable from the Tums variety. Maybe more Tums next time? We’ll see.
Try this at home!