Baking substitutions have a worse reputation than they deserve, mostly because the internet treats them all as equivalent. Some swaps are genuinely invisible: nobody has ever detected the difference between buttermilk and soured milk in a batch of scones. Others are damage limitation at best, and a few are the reason the cake came out like a frisbee. This page separates the three groups, with quantities.

A general note before the specifics: substitutions work best when you measure by weight. “One cup” of a replacement rarely behaves like one cup of the original, but 100g is 100g. The general-purpose swaps for non-baking cooking live in ingredient substitutions; the ingredient converter handles the cups-to-grams arithmetic when a recipe fights you on units.

Eggs

First, what the egg is doing, because the right substitute depends on the job. Eggs bind, they add moisture, they provide structure as their proteins set, and whisked eggs trap air. No substitute does all four.

Per egg, in things like muffins, pancakes, quick breads and everyday cakes:

  • Mashed banana, 60g (half a large one): binds and moistens well. Tastes of banana, which is either a feature or a problem.
  • Apple purée / unsweetened apple sauce, 60g: as above, nearly flavourless. Bakes come out slightly denser.
  • Ground flaxseed, 1 tbsp mixed with 3 tbsp water, rested 5 minutes: the mix turns gloopy and binds convincingly. Adds a faint nuttiness and works in anything rustic.
  • Plain yoghurt, 60g: good in muffins and quick breads, adds tenderness.
  • Aquafaba (the liquid from a tin of chickpeas), 3 tbsp: the only substitute that whips. It will make meringue, macarons and mousse, which no other egg replacement will.

The limit is quantity and role. A recipe using one or two eggs among flour, fat and raising agent will tolerate substitution. A recipe built on eggs (sponge whipped over six eggs, custard, pastry cream, soufflé) will not; the egg is the structure, and replacing it means finding a different recipe designed without it.

Checking whether the eggs you have are still usable is a different question, answered in how to tell if eggs are still good.

Butter

  • Baking block / hard margarine, 1:1 by weight: the closest swap in cakes and biscuits. Slightly less flavour, essentially identical behaviour. Soft tub spreads are not the same thing; they contain up to 40 percent water and will spread biscuits into lace and make cakes heavy.
  • Neutral oil, 80g per 100g butter: any refined oil from cooking oils and their smoke points works in muffins, brownies and loaf cakes, where it actually gives a moister crumb. It fails wherever the recipe creams butter with sugar for lift (a classic Victoria sponge) or relies on cold solid fat (shortbread, pastry, anything laminated). If the method says “cream” or “rub in”, oil is the wrong answer.
  • Coconut oil, 1:1 by weight: solid at room temperature, so it can stand in for butter in biscuits and pastry with some flavour change from virgin, less from refined.

Salted for unsalted butter is fine either direction: just add or omit roughly a quarter teaspoon of salt per 100g of butter.

Buttermilk

The easiest substitution in baking, and genuinely undetectable. Per 250ml of buttermilk:

  • 250ml milk plus 1 tbsp lemon juice or white vinegar, stirred and left for 5 to 10 minutes until it looks slightly curdled.
  • 190g plain yoghurt thinned with 60ml milk, or kefir straight, 1:1.

What matters is the acidity, which reacts with bicarbonate of soda to raise the bake and tenderises the crumb. Any of the above delivers it. Plain milk alone does not, and in a recipe raised with bicarb it will leave the bake flat and slightly soapy.

Self-raising flour and raising agents

Self-raising flour is nothing but plain flour with baking powder already mixed in, so the swap is exact:

  • Per 100g self-raising flour: 100g plain flour + 1.5 tsp baking powder (or per cup: 2 tsp). Add a small pinch of salt if the recipe has none.

The reverse also works: self-raising flour in a recipe calling for plain flour plus baking powder, adjusting the powder down accordingly. What does not work is ignoring the difference. Plain flour where self-raising was expected gives you a brick; self-raising in shortcrust pastry gives you a puffy, cakey shell.

Baking powder and bicarbonate of soda are not interchangeable either. Bicarb is pure alkali and needs an acid in the recipe (buttermilk, yoghurt, lemon, treacle, cocoa) to react with; baking powder is bicarb with its own acid built in. To replace 1 tsp baking powder, use ¼ tsp bicarb plus ½ tsp cream of tartar, or ¼ tsp bicarb plus a tablespoon of lemon juice or vinegar in the wet ingredients. Replacing bicarb with baking powder alone takes three to four times the volume and can taste of it.

Sugar

  • Caster for granulated: interchangeable by weight in most baking. Granulated dissolves more slowly, which can leave speckled tops on delicate sponges and grittiness in meringue; a 20 second blitz in a food processor turns granulated into caster.
  • Soft brown for white, 1:1 by weight: works, adds caramel flavour and a little extra moisture and chew. Biscuits come out softer and darker.
  • Honey, golden syrup or maple syrup for sugar: possible with adjustments, not a straight swap. Use about 75g of syrup per 100g sugar, reduce other liquid in the recipe by roughly 2 tbsp per 100g swapped, and drop the oven by 10°C because syrups brown faster.
  • Cutting sugar: most everyday cakes tolerate a reduction of up to a quarter of the sugar with little harm. Beyond that you are changing texture and keeping quality, not just sweetness, because sugar holds moisture and tenderises. Sweeteners like erythritol or stevia blends need recipes written for them.

Where substitution ruins the bake

Some recipes are chemistry demonstrations with a serving suggestion, and in those the ingredients are not suggestions:

  • Meringue, macarons, pavlova: egg white and sugar are the entire structure. Only aquafaba substitutes, and it needs a recipe written for it.
  • Whisked sponges (genoise, Swiss roll): the eggs are the raising agent. No swap.
  • Laminated and rubbed-in pastry: needs cold solid fat. No oil, no soft spreads.
  • Shortbread: three ingredients, one of which is butter. Substitute it and you have made a different, worse biscuit.
  • Yeast: baking powder does not replace it. They raise dough by different mechanisms on different timescales, and a “quick soda bread” is the honest fallback, not a shortcut to a loaf of bread.
  • Anything already substituted twice. One swap is baking; three swaps is a new, untested recipe wearing the old one’s name.

The pattern behind all of these: substitution works when the ingredient is a contributor and fails when it is the architecture. Before swapping, ask what the ingredient is doing. If the answer is “holding the whole thing up”, go to the shop.