Cuajar leche con ácido no es un sustituto fiable del suero de leche
Cuajar leche con limón o vinagre como sustituto del suero es un truco común, pero no reproduce su textura ni su acidez.
The trick is to add a tablespoon of lemon juice or distilled white vinegar to a cup of milk. The acid clumps the milk proteins together in a way similar to how cheese curds form, a controlled coagulation that, in theory, thickens and acidifies the milk enough to replace the buttermilk.
Becky Krystal of the Washington Post isn't so sure. Comparing both with pH test strips, she found that the buttermilk had a pH of 5, while the milk and vinegar substitute registered a pH of 6. Since the scale tends to be acidic below 7, both are acidic, but the curdled milk doesn't have the same viscosity or such a pronounced acidity.
The difference matters in recipes like pancakes and cookies, where buttermilk reacts with baking soda and releases gases that make the batter rise. Because it's more acidic, buttermilk makes the product rise more. Krystal also noticed that the batter with curdled milk smelled like vinegar and was more runny, so it separated with the baking soda.
Texture is the other issue. Commercial buttermilk is thick and viscous because a culture of lactic acid bacteria is added, and some producers add powdered milk, stabilizers, or heat treatment to increase its thickness, Penn State food scientist Kerry Kaylegian explained to Krystal. Curdled milk, on the other hand, is much thinner: according to America's Test Kitchen, the lumps that form immediately don't thicken it, even after standing.
There are better substitutes. Kaylegian recommends kefir, a fermented dairy product with a consistency similar to whey and a pH of 4.6. If kefir isn't available, she suggests plain yogurt diluted with a splash of water or milk, and sour cream can be treated similarly.
America's Test Kitchen proposes another alternative: cream of tartar, a powdered acid that, in their tests, produced the same leavening effect as buttermilk at 1 1/2 teaspoons per cup of milk. They recommend mixing it directly with the dry ingredients, because it forms lumps in milk. And, as Krystal suggests, the simplest option is to use buttermilk.
