What's the difference between Baking powder and yeast?

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What exactly are baking powder and yeast?

Baking powder

Baking powder and soda, what's the difference?

Most commercially-available Baking powder are composed of a base, an acid and an inert starch (cornstach or potato starch for example).

The acid can be lemon juice, yogurt, buttermilk, cocoa or vinegar or honey.

The base is typically Sodium Bicarbonate, also known as bicarbonate of soda, baking soda, bread soda, cooking soda or simply bicarb!!

The base and the acid are going to react together in a very simple acid-base reaction that is going to release carbon dioxide.

This gas will be released into a batter or dough causing bubbles thus expanding the mixture.

The starch added to the baking soda is there to keep the powder dry to avoid reaction between the acid and the base even before you add it to your batter.

You can replace the baking soda by the bicarbonate of soda alone provided sufficient acid reagent is also added to the recipe!

Yeast

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Mixing some active dried yeast with warm water

A yeast is a live, single-cell fungus. Also called Baker's yeast, this strain of yeast is of the species Saccharomyces cerevisiae, the same species as the one used in alcoholic fermentation.

Yeast converts the fermentables sugars present in the flour/dough into the gas carbon dioxide (and ethanol that evaporates during baking). This released gas make the dough expanding or rising as gas forms pockets or bubbles. When the dough is baked, the yeast dies and the air pockets set, giving the baked product a soft and spongy texture. That is why the baker will let the dough rise several times so it can develop more completely before baking it.

So can we substitute one for the other?

As we can see, baking soda and yeast are both used to gas-fill the pastry making it soft and fluffy. The reason why we use one or the other is primarily for the distinctive flavor and aroma from the yeast; but also because the acid base reaction from baking soda is much quicker than the yeast action. 

Also, the yeast can die before acting if the water added to the flour is too hot.

To substitute yeast by baking powder, it is needed to use a double acting baking powder. A double acting baking powder contains two different acids, one that is going to work in a wet mixture at room temperature, and one that is not going react until the mixture is heated in an oven.

On this note, I would like to wish you all Happy Baking and a

FANTASTIC HAPPY NEW YEAR 2012

See you Soon for more Sexy Science,