Natural and alkalised cocoa are not the same ingredient

There is a short answer about cocoa powder in cakes and a useful one, and they are not the same. What follows is the useful one.

What the alkali treatment does

Cocoa solids straight from the bean are acidic, sharp in flavour and pale reddish brown in colour. Treating them with an alkali neutralises much of that acidity, darkens the colour and rounds the flavour into something smoother and less fruity.

The process is usually labelled as Dutch processed or alkalised, though some packets say nothing at all and leave you guessing. A very dark, almost black cocoa has usually been heavily treated, while a reddish brown one is more likely to be natural. If the packet lists an acidity regulator or a raising agent style additive among the ingredients, it has been treated.

Why the raising agent depends on it

Bicarbonate of soda needs an acid to react with, and in many older chocolate recipes natural cocoa is that acid. Swap in alkalised cocoa and the reaction is starved, leaving both a weak rise and an unpleasant soapy residue.

Weighed out, baking powder brings its own acid, so recipes written around alkalised cocoa use it and are unaffected by which cocoa you buy. Recipes using both raising agents are usually balancing a partly acidic batter, and they tolerate substitution better than either extreme. Reading the raising agent first tells you which cocoa the recipe was written for, even when the writer never said.

What cocoa does to the batter besides flavour

Cocoa powder is largely starch and protein with a proportion of fat, so it behaves partly like flour and partly like a fat. It absorbs a great deal of liquid, which is why chocolate cakes so often include extra milk, coffee or hot water.

In the tin, replacing flour with cocoa weight for weight removes gluten forming protein and gives a more fragile crumb. That fragility is why many chocolate cakes are made as oil cakes, which are more forgiving of a weak structure. Adding cocoa to a recipe that did not contain it therefore needs adjustments to both liquid and flour.

Colour and the pH of the batter

Cocoa pigments shift colour with acidity, which is why the same powder can bake reddish in one cake and near black in another. An alkaline batter, often from generous bicarbonate, pushes the colour darker and the flavour towards a smoother, less sharp profile. An acidic batter keeps the reddish tone, which is the origin of certain traditional red-tinged chocolate cakes.

Once the crumb sets, colour therefore tells you something about the chemistry rather than about the quality of the cocoa you used.

A very dark cake with a slightly slick, alkaline taste has usually had more bicarbonate than the acid could neutralise.

Blooming and dissolving

Mixing cocoa with a hot liquid before it goes into the batter dissolves the starch and releases more aroma than dry mixing does. The technique also removes lumps, which are hard to break up once cocoa has been sifted into a dry mixture. Hot water or hot coffee is often used, and the coffee is there to deepen the chocolate flavour rather than to be tasted.

At oven temperature, blooming in melted fat achieves something similar and suits recipes where the fat is added as a liquid. Either way, count that liquid as part of the recipe rather than as an addition, or the batter will be too loose.

Proving times are written for a warm kitchen, and yours may not be one.

Choosing between them in practice

For a recipe raised with bicarbonate alone, use the cocoa the recipe assumes, and natural is usually the safer guess. For a recipe raised with baking powder, either cocoa will work and the difference will be flavour and colour only. Alkalised cocoa suits recipes wanting a deep, mellow chocolate character, while natural cocoa gives a sharper, fruitier one.

Keeping one tin of each is more useful than trying to make one do both jobs across different recipes. When a chocolate cake has failed to rise for no obvious reason, the cocoa tin is worth checking before anything else.

The takeaway

Check the raising agent, then check the tin, because the two have to agree before anything rises.

Patience is an ingredient, and it is the one people leave out.