Bread - Starter ready for a refresh
Bread - Starter ready for a refresh

Baking Bread Series: The leavening

I am absolutely fascinated with the fact that inside every bread I bake, there is a science experiment going on. Today, we shall continue the Baking Bread Series by discussing what is arguably the most science-packed ingredient of them all – the leavening.

There are three families of leavening that can help bread rise. All of them work by trapping air bubbles in the gluten network and expanding it as the bread bakes. But whilst the results might be similar, they differ widely in composition and flavouring capacity. Let’s dive deeper.

Chemical leavening

Baking soda and baking powder belong to this family. They work by releasing carbon dioxide as a reaction to each other, moisture, or heat. Acid is a triggering agent for both, however, whilst the baking soda calls for an addition of an acidic ingredient, such as buttermilk or vinegar, the baking powder already contains it, most commonly in form of cream of tartar. Their flavouring capacity is mild, but overuse may cause a metallic, soapy taste. Irish Soda Bread is a classical bake in the category, but there are few others like Rum Raisin Bread.

Bread - Active starter
Bread – Active starter

Biological leavening

Biological leavening works by fermenting simple sugars into carbon dioxide. When flour meets water, the mighty gluten is formed. But gluten is not the only inhabitant of this settlement. Yeast and bacteria move in almost immediately and begin to team up. They organise themselves into two communities – the baker’s yeast (only yeast), and/or the sourdough starter (yeast and bacteria).

Yeast and bacteria live around us, in the air, on our hands, jars, etc. They feed on wheat starch broken into simple sugars by the enzyme called amylase, present in flour and activated with water. During this feast, the yeast delivers ethanol and carbon dioxide responsible for the rise and the bacteria produces lactic acid and some acetic acid responsible for acidity, hence the name sourdough.

The interaction of the two is a true manifestation of the survival of the fittest as remarkably only good bacteria can tolerate ethanol, and only one kind of yeast is able to survive in the acidic environment. It is known as Saccharomyces cerevisiae, the baker’s yeast.

Now produced industrially, this yeast comes in several forms, like active dry yeast, instant yeast and fresh yeast, all ready for use. When bread bakes, ethanol and carbon dioxide evaporate, but acids remain contributing to the sourness of the finished loaf. This is why sourdough leavening is so much more flavourful in comparison to only yeast-leavened breads.

Bread - Just refreshed
Bread – Just refreshed

As a living community, the sourdough starter depends on the availability of food, temperature and time, hence it always needs a refresh of starch containing flour. The higher temperatures increase the feeding frenzy and lower ones slow it down.

Many bakers treat their starters as pets and, as all pets, they get names; for instance, Bread Pitt, Clint Yeastwood, or Puff Daddy. There are as many starters as there are bakers, so much so that in 2013, Puratos launched in Belgium the world’s only sourdough library with a collection of about 130 sourdoughs from over 23 countries.

Mechanical leavening

Last but not least, a quick note on mechanical leavening that is rarely applied in bread baking. Heavy cream or egg whites are used for this purpose. They trap air when beaten, and when subsequently added to the bake, further expand when cooked. This is a most common method in making sponge cakes and soufflés and even Yorkshire pudding!

To be continued …

By Dr. Irina Mikhailava
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Dr. Irina Mikhailava, a chef and a good food champion, happily residing in the Algarve and eating all over the world with an appetite for learning, sharing and writing. Instagram: incompanyoffood