It turns out the the buttermilk we get in stores isn't the real thing anyway--the use of pasteurized milk means bacteria needs to be added, along with thickening agents--so why not just make your own? All the taste tests I've seen say there's no difference in the final recipe results that use buttermilk as an ingredient. Here are two recipes, one from Cooks Illustrated and one from the Food Network.more
Adapted from thekitchn.com
cup milk (any kind, but best not to be less than 2percent)
Tablespoons (4-½ teaspoons) lemon juice
teaspoons (1 Tblsp + 1-½ tsp) white vinegar or lemon juice
scant cup milk
COOKS ILLUSTRATED Take 1 cup of milk, stir in 1 1/2 tablespoons lemon juice, and let sit for a good five minutes; the mixture will begin to thicken to a buttermilk-like consistency. Use this mixture as you would buttermilk, and you'll never be without fluffy pancakes again. FOOD NETWORK - EMERIL LAGASSE Place the vinegar in a glass-measuring cup, and add enough milk to make 1 cup total liquid. Stir to combine and let stand for 10 to 15 minutes (The mixture will begin to curdle). Use as needed in a recipe, or cover and refrigerate until needed.