Buttermilk substitute: what works and how much to use

How to make a buttermilk substitute with lemon or vinegar

1. Pour 1 tablespoon (15 ml) of lemon juice or distilled white vinegar into a liquid measuring cup.
2. Add milk up to the 1-cup line (240 ml).
3. Stir, and use it in place of 1 cup of buttermilk.

Filling to the line keeps the total at 1 cup, so the batter is no wetter than the recipe expects. Most recipes, and Texas A&M AgriLife Extension's substitution chart, use 1 tablespoon of either acid. America's Test Kitchen uses 1½ tablespoons when it's lemon juice. White vinegar disappears in the oven. Lemon leaves a faint citrus note that suits muffins and pancakes.

Do you have to let it sit?

Recipes usually say 5 to 10 minutes. America's Test Kitchen baked biscuits and pancakes with rested and unrested lemon milk and found them virtually identical, because the acid works the moment it meets the milk. Stir it first and measure everything else while it stands.

What the acid does

The flecks in the cup are milk protein. Acid changes the electrical charge on casein, milk's main protein, and the casein clumps into small curds. Cultured buttermilk gets its acid slowly, from bacteria turning milk sugar into lactic acid, and the same proteins set into a smooth gel. So soured milk looks curdled but stays thin, and buttermilk pours thick. In America's Test Kitchen's tests, drop biscuits and pancakes made with soured milk spread more than they should have. Cakes, held in by the pan, didn't mind.

How much lemon or vinegar for ¼, ½ or ⅔ cup?

1 tablespoon per cup is 3 teaspoons, so every ⅓ cup of buttermilk takes 1 teaspoon of acid. Put the acid in the measuring cup first, then add milk to the line you need.

For lemon juice at America's Test Kitchen's stronger ratio, add half as much again: 2¼ teaspoons for ½ cup, 1 tablespoon for ⅔ cup. A ⅜ teaspoon is a ¼ teaspoon plus a ⅛.

For a recipe in milliliters, Hedgehog Chef's free cooking converter turns cups into milliliters and back. To halve a recipe that wants ⅔ cup of buttermilk, the recipe scaler does the whole ingredient list in real fractions: ⅓ cup of buttermilk, never 0.333.

What else can you use instead of buttermilk?

Anything with acid and some body, closest first:

• Plain yogurt, thinned: ½ cup whole or low-fat yogurt plus ½ cup water for each cup of buttermilk. America's Test Kitchen found it more or less identical to buttermilk in acidity and thickness, the best swap for biscuits and pancakes.
• Greek yogurt: ⅓ cup plus ⅔ cup water or milk. In King Arthur Baking's side-by-side test, Greek yogurt and milk came a close second to buttermilk in biscuits and tied with it in pancakes.
• Kefir, 1 for 1. It's cultured milk too. Pancakes and biscuits brown a little faster with it.
• Sour cream, thinned with milk or water until it pours like heavy cream. It's richer, so use it in cakes and quick breads.
• Cream of tartar: 1½ teaspoons per cup of milk, the amount America's Test Kitchen uses (King Arthur uses 1¾). Biscuits and pancakes made this way came out as light as buttermilk ones with no off-flavors, though King Arthur's tasters found them short on depth. It's the swap for anyone who can taste lemon in a pancake.
• Powdered buttermilk: buttermilk, dried. Follow the chart on the label, whisk the powder into the dry ingredients and add the water with the wet ones.

Why do recipes call for buttermilk, and which swap suits which recipe?

Mostly for its acid. Buttermilk's lactic acid reacts with baking soda to make carbon dioxide, and those bubbles lift soda bread and pancakes. The acid also gives the tang, and buttermilk's thickness keeps a drop biscuit standing up. Without acid the soda has nothing to react with. In King Arthur's test, plain milk gave pancakes that rose less and a cake that came out darker and denser.

• Biscuits, pancakes, waffles and other plain recipes where the flavor shows: thinned yogurt or kefir.
• Cakes, muffins and quick breads with brown sugar, spice, chocolate or bananas: any acidic swap. Every one worked in King Arthur's buttermilk cake.
• A buttermilk soak for fried or roast chicken: thinned yogurt or kefir. Both are cultured, with the same mild lactic acid and enough body to help the flour stick. For the leftovers, see how long cooked chicken keeps in the fridge.

The smaller the amount, the less it matters. King Arthur reckons a recipe with ¼ cup of buttermilk and no baking soda will be fine with plain milk.

Can you make buttermilk with almond, oat or soy milk?

Yes, and soy milk is the one to reach for. Use the same ratio, 1 tablespoon of lemon juice or vinegar per cup, with an unsweetened, unflavored carton.

What the acid thickens is protein. Fortified soy drinks are the only plant milks the Dietary Guidelines count with dairy, because their main nutrients, protein among them, are similar to milk's, and soy milk thickens much like dairy milk. Almond and oat milks usually have far less protein, so they stay thin. Their acid still reacts with the baking soda, so a cake will rise, but expect a looser batter. Compare the protein line on the Nutrition Facts label (the FDA's guide to milk and plant-based drinks shows where to look).

With dairy milk, any fat level works. Buttermilk is never more than 3.25 percent fat, the same as whole milk, and America's Test Kitchen's tasters could tell little difference between whole, low-fat and nonfat buttermilk in baking.

When shouldn't you substitute buttermilk?

When buttermilk is the main flavor. Buttermilk ranch or blue cheese dressing, buttermilk pie, chilled buttermilk soups and a glass of it straight all depend on the cultured taste, and soured milk has the sourness without it. King Arthur's advice is the same: when buttermilk is the main ingredient, buy cultured buttermilk.

If the store is out, thinned yogurt or kefir makes a decent dressing because both are cultured. Lemon milk tastes of lemon and milk.

What to do with leftover buttermilk

Go by the date on the carton. Kansas State University's extension storage chart gives buttermilk 3 to 5 days in a fridge at 40°F (4°C) or below, and says to cover it tightly and mix it before using.

The same chart says not to freeze it, because it separates. For baking it doesn't matter. America's Test Kitchen froze buttermilk for up to a month with no noticeable effect on baked goods. Freeze it in an ice cube tray or in ½-cup portions, as King Arthur does, then bag it. Thaw it overnight in the fridge and whisk it back together. Use it for baking and marinades, where the separation doesn't show.

To use up a quart: weekend pancakes, soda bread, mashed potatoes, a chicken soak, cornbread in a hot skillet (if the pan has gone sticky, see how to season cast iron), or a dressing with dill and chives, which keep longer if you store fresh herbs the right way.

In Hedgehog Chef, add the open carton to the pantry with its date and you get a reminder before it turns. The shopping list made from the week's plan skips what's already in the pantry, so buttermilk lands on the list when there's none at home, before you're halfway through the batter.