Welcome back: let's talk about lift
Last time we met flour, sugar and fat. Those three give a bake its body, its sweetness and its tenderness. On their own, though, they'd mostly give you something flat and heavy.
So what makes a sponge light, a scone tall and a loaf airy? That's today's question. We'll look at two groups of helpers: eggs, and the raising agents, meaning baking powder, bicarbonate of soda and yeast.
Ready? Let's crack on. (Sorry, I couldn't resist.)
Eggs: three jobs in one shell
You might think of an egg as one ingredient. In baking it's really two, the white and the yolk, and each has its own job.
Here are the three big things eggs do:
- They bind. Egg holds the other ingredients together so your bake doesn't crumble apart.
- They set. As egg heats up, its proteins firm up. That gives the bake its structure, a bit like scaffolding going up around a building.
- They trap air. Whisk an egg and you're folding in thousands of tiny bubbles.
The white: your bubble-builder
Egg white is mostly water and protein. When you whisk it, the proteins unwind and stretch out. Then they link up with each other into an elastic web that wraps around each air bubble and holds it in place.
Think of a crowd of people letting go of their own hands and joining up into a big net. That net is your foam. Egg whites can swell to as much as eight times their original volume, which is why they're the secret behind airy bakes.
Here's a question for you. What do you think happens if a speck of yolk sneaks into the whites?
The answer: they won't whip properly. Any fat gets in the way of the protein net, whether it's a trace of yolk, a greasy bowl or buttery beaters. So when a recipe asks for whisked whites, use a spotlessly clean bowl and separate your eggs carefully.
The yolk: richness and the great peacemaker
The yolk is where the fat lives, so it brings richness, colour and a tender crumb.
It also contains lecithin, a natural emulsifier. You know how oil and water won't mix? Lecithin is the peacemaker. One end of it likes water and the other likes fat, so it wraps round tiny droplets of fat and keeps them spread evenly through the watery parts of a mixture. That's a big reason a cake batter stays smooth instead of splitting.
So here's the short version. Whites build and hold air. Yolks enrich and emulsify.
Bicarbonate of soda: the one that needs a partner
Now for the raising agents. All of them do the same basic thing: they make bubbles of carbon dioxide gas. The heat of the oven makes those bubbles expand, and the bake rises around them.
Bicarbonate of soda (called baking soda in the US) is pure sodium bicarbonate. It's an alkali, and it only fizzes properly when it meets an acid.
So when you see bicarb in a recipe, look for its partner. Common acidic ingredients include:
- buttermilk or natural yogurt
- lemon juice or vinegar
- dark treacle
- natural (non-alkalised) cocoa powder
What happens if there isn't enough acid? The leftover bicarb gives a soapy, metallic taste and can turn the crumb an odd colour. Bicarb is also powerful stuff, roughly three to four times stronger than baking powder, so a little goes a long way.
Baking powder: the all-in-one kit
Baking powder is bicarbonate of soda that comes with its partner already packed. It's bicarb plus a dry acid, plus a little starch to keep the two apart and dry in the tub.
Add liquid and the acid and alkali get to work, no buttermilk needed. That makes baking powder the go-to for recipes made with plain milk, which doesn't bring enough acid of its own.
You'll also meet self-raising flour. That's simply flour with baking powder already mixed in.
So how do you choose? It's simple. Acidic ingredient in the recipe? Bicarb can be used. No acid? You need baking powder. Some recipes use both, with bicarb to balance the acid and baking powder for extra lift.
Yeast: the living raising agent
Yeast works differently, because it's alive. It's a tiny fungus that feeds on sugars in the dough and gives off carbon dioxide and a little alcohol. It's slower than baking powder, and that slowness builds flavour. We'll get our hands properly into yeast doughs a little later in the course. For now, just remember that yeast makes gas by living and feeding, not through a quick chemical fizz.
Too much, too little: reading the signs
So how do you know if the raising agent was off? Your bake will tell you.
Too much raising agent makes too much gas. The bake shoots up in the oven, then the structure can't hold it and it sinks back, often leaving a coarse, holey crumb. With too much bicarb you may taste that soapy, metallic note too.
Too little, or raising agent that's past its best, gives you a flat, dense, heavy bake.
Here's a handy check for old tubs. Put about 2 teaspoons of baking powder in a cup and pour over some hot water. It should fizz straight away. For bicarb, drop a pinch into a spoonful of vinegar and look for a lively fizz. No fizz? Time for a new tub.
Key takeaways
- Eggs bind, set and trap air.
- Whites whip into a protein foam that holds air. Keep fat, including yolk, well away from them.
- Yolks add richness, and their lecithin emulsifies fat and water.
- Bicarbonate of soda needs an acid, such as buttermilk, yogurt, lemon or treacle.
- Baking powder is bicarb with its own acid built in. Self-raising flour already contains it.
- Too much raising agent means a rise then a sink and a coarse crumb. Too little means flat and dense.