Why do some pie crust recipes call for vinegar?
Vinegar can affect the gluten development in dough. Gluten gives dough structure, but too much gluten development can make dough tough. Acid can hinder gluten development; so, a bit of vinegar (or lemon juice) can make pie dough slightly more tender. But the math—and thus the technique—is a little fussy. In order to reap the tenderizing effects of acidic ingredients, the overall pH of the dough must be below 5; at pH between 5 and 6, gluten development actually increases.
We tested various amounts of vinegar and found that for dough with 2½ cups of flour (enough for a double crust pie), we needed 1¾ teaspoons of vinegar to get the pH below 5. Some tasters were able to detect the tangy flavor of the vinegar in an unfilled pie crust, but it went nearly unnoticed in an apple pie.
THE BOTTOM LINE A little vinegar in a pie dough recipe can tenderize the crust, but be careful: Too little can actually toughen the crust, and too much can harm its flavor.
