Kitchen Chemistry: pH and Leavening

There are a number of cookbook authors out there that are popular with the kosher kitchen crowd. I hesitate to disparage them publicly, because I certainly don’t want to invite criticism of my as-of-yet unpublished (okay fine, unwritten) cookbook. However, when I see something as egregious as a violation of the laws of chemistry, I can’t sit back silently.

Chemistry 101

All substances have what is known as a pH value. pH stands for percent hydrogen. This refers to the number of free hydrogen ions (hydrogen atoms that aren’t hooked onto other atoms) it has. The more there are, the more acidic it is. On the other end of the spectrum, the higher the number of OH ions (an oxygen only connected to one hydrogen, leaving another hook, or bond, free), the more alkaline it is. When you add something with H ions and OH ions, you get HOH, or more commonly, H2O. You also get heat as a byproduct of the reaction (exothermic). And salt. So something with an equal balance of acidic and alkaline ions is neutral. It’s sometimes called water. On the pH scale, a value of 7 is pH neutral. From 7 down to 1 is an increase in the acidic level. From 7 up to 14 is an increase in the alkaline level.

Food Chemistry 203

When you add an acid and an alkaline together, you get – as I mentioned above – water, salt, and heat. In baking we care about the heat generated. Because when you heat air, it expands. When you mix it into something with an elastic protein structure (i.e. gluten), the expanding air is trapped. When you use yeast, the little beasties give off carbon dioxide. When you mix an acid and an alkaline, you get chemical leavening. The result? Light, airy cakes and breads.

The balance of acid and alkaline in a recipe is the reason you can’t “throw together” a bunch of ingredients and hope for a cake. You have to know what you are doing in order to get the density (‘rise’ or ‘crumb’) you’re looking for. So recipe developers, chefs, bakers and their ken work to perfect their recipes by balancing these two elements. At least that’s what they’re supposed to do.

Orange juice (citric acid), cream of tartar (tartaric acid), vinegar (acetic acid), wine (tannic acid), tea (tannic acid), and milk (lactic acid) all have a pH of less than 7. On the greater than side, baking soda (sodium bicarbonate) is the most common alkaline in cooking. Many fruits are alkaline as well. Baking powder is actually a balance of baking soda and an acid (a phosphate or sulfate), so it’s a self-contained leavening agent that works first when moistened, then when heated, also known as “double acting”.

The Cow Juice Conundrum

In the realm of kosher foods, it is common to substitute ingredients that would otherwise render a recipe unusable. Oil or margarine for butter is a well-known example. But, things get trickier when it comes to milk. Milk has a pH of just under 7, which makes it an acid. Soy milk and almond milk, however, are alkaline. This presents a major problem, obviously, since these are the two main substitutions for milk in kosherized recipes. If the recipe 1) contains only baking soda; 2) relies on the acidity of milk to produce chemical leavening; and 3) doesn’t get any, you won’t get the results you expected. The batter won’t rise properly, and you’ll be left with a product much more dense than you expected, and it might have a metallic taste as well.

The Fix

In order to remedy this situation and wind up with the results you expect, you are going to have to be smarter than the recipe. If, when reading through a recipe you notice baking soda and some non-acidic liquid (soy milk or almond milk, or even non-dairy creamer) as a ‘substitution’ for what would have been regular milk, you’re going to have to swap out the baking soda for two times the baking powder. In other words, replace 1/2 teaspoon of baking soda with 1 teaspoon of baking powder. If a recipe has baking soda and baking powder, you can get away with substituting baking powder for baking soda one-for-one. These aren’t absolutes, and you might have to note in your recipe book what you’ve tried and when.

Recipes should be tried and tested by their authors to ensure the results are exactly what is expected. When someone plagiarizes a recipe in order to bulk up a book just to sell it for more money, the unsuspecting public is left blindly following recipes that are… half-baked.

Note: The truth is that originally I was going to publicly blast a cookbook author for this lapse of kitchen common sense, but I don’t remember where it was that I first saw the problem recipe. It might have been in a kid’s cookbook.