Baking substitutions that work: buttermilk, eggs, self-raising flour and more

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You are halfway through a recipe and something is missing. Some ingredients can be swapped with almost no difference; others change the result more than you might expect. These are the substitutions bakers rely on, with the catches to know about.

Buttermilk

Buttermilk is acidic, which tenderises and reacts with bicarbonate of soda to help a bake rise. To replace it:

Stir 1 tablespoon of lemon juice or white vinegar into enough milk to make 240ml (about a cup), and leave it for 5 to 10 minutes until it thickens slightly and curdles.
Or thin natural yoghurt with a little milk to a pourable consistency.

Both work well in scones, pancakes, soda bread and cakes. Plain milk on its own is not a good swap where the recipe relies on bicarbonate of soda, because there is nothing acidic to activate it.

Self-raising flour

Self-raising flour is plain flour with raising agent already mixed in. To make your own:

Add about 2 teaspoons of baking powder to every 150g of plain flour, and sift or whisk them together well.

Sources vary a little, and some use less, so treat that as a starting point. The reverse is the classic mistake: if a recipe uses plain flour plus baking powder and you only have self-raising, leave out most or all of the baking powder, or the cake may rise and then collapse.

Baking powder vs bicarbonate of soda

They are not interchangeable one for one.

Bicarbonate of soda (baking soda) is a pure alkali. It needs an acid in the recipe, such as buttermilk, yoghurt, lemon juice, brown sugar, honey or cocoa, to react. It is much stronger than baking powder, and too much tastes soapy or metallic.
Baking powder is bicarbonate of soda with an acid already added, so it works on its own.

If you have no baking powder, you can mix bicarbonate of soda with an acid such as cream of tartar, but for a first attempt it is safer to choose a different recipe. Replacing bicarbonate with baking powder needs a lot more powder and can change the flavour and browning.

Eggs

Eggs bind, add moisture and help a bake rise. Swaps work best where the recipe uses only one or two eggs:

Flax egg: 1 tablespoon of ground flaxseed mixed with 3 tablespoons of water, left to thicken for a few minutes, replaces one egg in muffins, cookies and brownies. Chia seeds work the same way.
Mashed banana or apple purée (about 60g per egg) adds moisture and binding, but also flavour and density.
Natural yoghurt (about 60g per egg) suits cakes and muffins.

Avoid substitutes in recipes where eggs are the main structure, such as sponge cakes made by whisking eggs, meringues, soufflés or custards. They will not work the same way.

Butter vs oil

Oil makes cakes moist and tender and keeps them soft for longer, but it cannot be creamed with sugar to trap air, so you lose some lift and butter flavour. Use about three-quarters of the weight of butter in oil, and choose a recipe written for oil if you can.
Butter cannot simply replace oil in a recipe built around it; melt it and expect a slightly firmer crumb.
In biscuits, pastry and shortbread, oil is a poor swap for solid butter, because the texture depends on solid fat.
Baking spreads vary in fat and water content; check that the label says it is suitable for baking.

Sugar

Caster and granulated sugar can usually swap, though granulated may give a slightly grainier texture in delicate sponges. Blitzing granulated in a blender briefly makes it finer.
Light and dark brown sugar swap with each other; dark gives a deeper flavour and colour. Brown sugar in place of white makes bakes moister and chewier.
Honey or syrup in place of sugar adds liquid, browns faster and changes the texture. Reduce other liquid and lower the oven a little.
Cutting sugar: you can often reduce it a little in cakes and muffins, but sugar holds moisture and affects texture and browning, not just sweetness. Large cuts give dry, pale, tough results.

Milk and cream

Most plant milks work in place of dairy milk in cakes and pancakes.
Single cream mixed half and half with milk can stand in for whole milk. For double cream that needs whipping, there is no reliable homemade substitute.

A rule of thumb

Swap one ingredient at a time and make a note of what you changed. Then you know what to thank or blame. Which substitution has saved a bake for you, or gone badly wrong? Share it, or ask about a swap, in the comments.