Use soy milk and vinegar instead of buttermilk at 1 tbsp vinegar per cup of soy milk, rested 5 minutes. Buttermilk and soy milk and vinegar do similar work in a recipe, but they are not identical, and the ratio is what makes the swap succeed. This guide gives the exact ratio, an equivalence table for every amount you will need, what changes in the finished dish, and when you should not make the swap at all. All ratios on this page come from the CookScale substitution data, and every result is approximate; taste the dish before serving, and adjust the seasoning if the swap changes the flavour.
Buttermilk to Soy milk and vinegar: equivalence table
The table below scales the ratio — 1 tbsp vinegar per cup of soy milk, rested 5 minutes — to every amount you will need, from a quarter of a cup up to three cups. Use the row that matches your recipe, and do not guess the scaling in your head, because a small error in the ratio grows with the size of the recipe.
| Buttermilk needed | Soy milk | White vinegar | Rest |
|---|---|---|---|
| 1/4 cup | 1/4 cup | 3/4 tsp | 5 minutes |
| 1/2 cup | 1/2 cup | 1 1/2 tsp | 5 minutes |
| 1 cup | 1 cup | 1 tbsp | 5 minutes |
| 2 cups | 2 cups | 2 tbsp | 5 minutes |
| 3 cups | 3 cups | 3 tbsp | 5 minutes |
When a recipe calls for an amount that is not in the table, scale the ratio proportionally: work out how many cups of buttermilk the recipe needs, then multiply the ratio by that number. For a single cup, the ratio is exactly as stated; for half a cup, halve it; for two cups, double it. Keep the recipe scaler open while you cook, and you can scale the whole recipe, including the substitution, in one step.
What changes when you use soy milk and vinegar instead of buttermilk
Soy milk soured with vinegar is the dairy-free, nut-free version of buttermilk, and it behaves the same way in baking: the acid activates the baking soda, tenderises the crumb and adds a tang. The main differences are the flavour and the richness: soy milk has more protein than other plant milks, so the bake sets slightly more firmly, and it has a beany taste that some people notice. The vinegar adds no flavour of its own, so the result tastes cleaner than the lemon juice version, which suits a plain cake or a chocolate cake. The rise is the same, because the acid does the same work, and the crumb is just as tender. In a marinade, the soured soy milk tenderises the meat or the tofu in the same way as buttermilk. In a dressing, the difference is bigger, because soy milk is thinner than buttermilk and the dressing will be runny.
When not to substitute buttermilk with soy milk and vinegar
Do not use plain milk — without acid, baking soda will not activate and the bake can taste soapy. That rule is the most important part of this page, because a substitution that works in one recipe can fail badly in another. Buttermilk does a specific job in each recipe, and the swap only works when the substitute can do the same job. In a recipe where buttermilk is the main structure — where it holds the bake together, or where its flavour is the point of the dish — the substitute will not do, and it is better to wait until you have the real ingredient, or to choose a different recipe. In a recipe where buttermilk is a supporting ingredient, where it adds moisture, richness or flavour but does not carry the dish, the swap usually works well. The test is simple: if removing the buttermilk would ruin the recipe, do not substitute it; if the recipe would still work without it, the substitute is probably safe.
Why this swap works
The acid in buttermilk activates baking soda and tenderises crumb; any acidic milk works the same way. That is the principle behind the swap: the substitute does the same chemical or structural job as the original, even though it looks and tastes different. The acid in an acidic substitute activates baking soda, the fat in a fatty substitute shortens a dough, and the liquid in a liquid substitute hydrates the flour. When the substitute does the same job, the swap works; when it does a different job, the swap fails. The ratio on this page is the amount that makes the substitute do the same job as the original, and it is worth following exactly, rather than guessing, because a small error in the ratio changes the job the substitute does.
Worked examples: buttermilk to soy milk and vinegar in real recipes
1. Vegan chocolate cake without dairy
A vegan chocolate cake needs a cup of buttermilk, so stir a tablespoon of white vinegar into a cup of unsweetened soy milk and leave it for five minutes. The vinegar version is better than the lemon juice version for a chocolate cake, because it adds no citrus note, and the soy milk has more protein than other plant milks, so the cake sets firmly. Pour the soured soy milk into the batter exactly where the buttermilk would have gone, and bake the cake as usual.
2. A dairy-free, nut-free muffin batch
A batch of dairy-free muffins needs two cups of buttermilk, so stir two tablespoons of white vinegar into two cups of unsweetened soy milk and leave it for five minutes. The soured soy milk gives the muffins the same tang and the same lift as buttermilk, and the swap is both dairy-free and nut-free, which suits a school lunchbox. Use unsweetened soy milk, and do not change anything else in the recipe, because the swap is a straight replacement for the liquid.
3. A dairy-free marinade for chicken
A marinade for chicken needs a cup of buttermilk, so stir a tablespoon of white vinegar into a cup of unsweetened soy milk and leave it for five minutes. The soured soy milk tenderises the chicken in the same way as buttermilk, because the acid breaks down the proteins, and the soy milk has enough body to cling to the meat. Marinate the chicken for at least an hour, or overnight for the best result, and turn it halfway through to coat it evenly.
How to make the swap
Pour the soy milk into a measuring jug, stir in the white vinegar, and leave the jug on the counter for five minutes. The soy milk will thicken slightly and may curdle a little, which is normal and exactly what you want: the curdling shows that the acid is working. Use the soured soy milk straight away, before it separates too much, and stir it into the batter exactly where the buttermilk would have gone. Use unsweetened soy milk, because sweetened soy milk adds sugar the recipe did not ask for. Use white vinegar, not malt or balsamic, because those add colour and flavour the recipe did not ask for. Do not skip the resting time, because the acid needs a few minutes to work on the milk.
Common mistakes
The most common mistake is using sweetened soy milk, which adds sugar the recipe did not ask for and can make a savoury dish taste odd. Use unsweetened soy milk. The second mistake is skipping the resting time and using the milk straight away, before the acid has had time to work. Rest it for five minutes, or the baking soda will not activate properly. The third mistake is using the wrong vinegar: malt vinegar adds colour and a strong flavour, and balsamic vinegar adds sweetness and colour, so use plain white vinegar. Finally, do not use this swap in a recipe where the richness of buttermilk matters, such as a creamy dressing, because soy milk is thinner and the dressing will be runny.
Frequently asked questions
How do I make dairy-free buttermilk with soy milk?
Add 1 tablespoon of white vinegar per cup of unsweetened soy milk, and rest the mixture for 5 minutes. The soy milk thickens slightly and may curdle a little, which is normal and shows the acid is working. Use the soured soy milk straight away, and stir it into the batter exactly where the buttermilk would have gone.
Is this swap nut-free as well as dairy-free?
Yes. Soy milk contains no nuts, so this swap is both dairy-free and nut-free, which makes it suitable for a school lunchbox or a nut-free household. Check the carton for allergen warnings, because some soy milks are made in factories that handle nuts, and choose a brand that is certified nut-free if the allergy is severe.
Does soured soy milk activate baking soda?
Yes. The vinegar makes the soy milk acidic, and the acid activates baking soda in exactly the same way as buttermilk, giving the bake its rise and its tender crumb. The rise is the same, and the crumb is just as tender, although the bake may be slightly firmer, because soy milk has more protein than other plant milks.
Can I use malt vinegar instead of white vinegar?
It is better not to. Malt vinegar adds colour and a strong, malty flavour that the recipe did not ask for, and it can darken a pale cake. Balsamic vinegar is worse, because it adds sweetness and a dark colour. Use plain white vinegar, which adds acid and nothing else, so the bake tastes clean.
Can I use this swap in a dressing?
It is not ideal. Soy milk is thinner than buttermilk, so a dressing made with soured soy milk will be runny and light, and it will not have the richness of a buttermilk dressing. For a dairy-free dressing, a better choice is a plant-based yogurt, which is thicker and tangier, and gives a creamier result.