No buttermilk? Add 1 tbsp lemon juice or vinegar to milk to make 1 cup; the simple substitute only needs a few minutes to thicken

You are halfway through a scone recipe and you realize there is no buttermilk in the fridge. Don't panic, and don't run to the store just yet. The Oregon State University Extension Service offers an easy fix. Put a tablespoon of lemon juice or vinegar in a measuring cup and fill it with milk to the one-cup mark. Stir it up, then leave it alone. In a few minutes, the milk will thicken, taste a little sour and be ready to use instead of real buttermilk. It’s not magic; it’s good food chemistry that makes this kitchen fix work.

How lemon juice or vinegar works on milk

Milk looks smooth because it contains small, evenly distributed clusters of proteins called casein micelles. These clusters carry a negative charge, so they repel one another. However, upon the addition of an acid such as lemon juice or vinegar, positively charged hydrogen ions are formed. The hydrogen ions neutralize the negative charge of the clusters and make the proteins come together. This process is called coagulation, the same reaction that turns milk into curds in soft cheeses like paneer or ricotta. Scientists refer to the exact pH at which this occurs as the isoelectric point of the protein.

A 2022 study, ‘Acid and Rennet Coagulation Properties of A2 Milk,’ published in the journal Foods, by researchers Bibiana Juan and Antonio-José Trujillo, tracked this process directly. The study observed how long it took for the samples of milk, varying in their casein composition, to achieve the pH of about 4.6, at which stage casein proteins became neutral and began to coagulate. This is roughly the pH value that home cooks achieve when adding lemon juice or vinegar to milk. That’s also why the mix only needs a short rest. The milk and acid react almost immediately, and a few minutes is usually enough for the mixture to thicken and form small curds.

What this means for your scones

Buttermilk in a recipe isn't just for tang. Most recipes for scones and biscuits call for baking soda, and baking soda needs an acid to work its magic. According to a 2025 technical report from the USDA Agricultural Marketing Service on ammonium bicarbonate and carbonate, sodium bicarbonate (the chemical name for baking soda) must react with an acid to create enough carbon dioxide gas to allow many baked goods to rise properly, including scones. That gas is what creates the little pockets of air that make scones seem light and not heavy. Recipes that use only baking powder don't need to make this swap as much because baking powder has its own acid. So, when you substitute acidified milk for buttermilk, you're doing more than altering the flavor. You are giving the baking soda the acid it needs to make your bake rise.

How to make the substitute yourself at home

Pour one tablespoon of fresh lemon juice or plain white vinegar into a liquid measuring cup. Then add milk slowly until the mixture reaches one cup and mix gently just enough to combine. Let it sit for a few minutes until the mixture is slightly thickened with small flecks. Once it reaches that stage, use it exactly as the recipe calls for buttermilk, cup for cup.

Tips for doing it right

According to baking guides like Preppy Kitchen, adding whole milk or two percent milk gives the texture that is similar to real buttermilk, because the fat helps the mixture thicken. You can also use skim milk, but the result will be thinner. The same sources note that this trick may not work as well with lower-protein nondairy milks such as almond or oat milk because there is less protein for the acid to react with. Let the mixture sit for a bit before using. If you rush this step, the acid won't have fully reacted, and the batter may not rise as much. A single gentle stir is all it takes. Overmixing will not make the thickening happen faster or improve it.

Also, this substitute is not really the same as store-bought buttermilk, as that is made by a fermentation process with live cultures of bacteria, not just a quick splash of acid. The flavor is a little milder, but the homemade version works for most baking recipes, like scones, pancakes and biscuits.

A pantry trick that usually works

Running out of buttermilk doesn’t have to derail a recipe. One tablespoon of lemon juice or vinegar mixed with milk mimics the acidity that buttermilk lends to a recipe, for both flavor and for the chemical reaction that helps baked goods rise. The science that underlies it is straightforward. The acid changes the charge of the milk proteins so they thicken, and that same acid activates the baking soda that’s already in your batter. The next time a recipe calls for buttermilk and your fridge falls short, this simple swap can get your scones to the oven without a trip to the store.