Thursday, July 06, 2006

What About Sourdough?

In my recent explorations of my new home, which was not entirely devoid of remnants from the former tenants, I came across a bread maker in one of the top shelves of the kitchen. As I have been determined to become a do-it-yourself bread maker for some time now, the bread maker was the perfect excuse to get a start on that, at least half-assedly.

One bread type that has always fascinated me for its flavor and origin is sourdough (yogurt does as well, for similar reasons, but that is the stuff for another post). Is the sour flavor from yeast or bacteria alive in the food? How does our body deal with the organisms which cause this inviting tangy flavor? The bread maker also turns out to be a perfect excuse to look to the web and research this topic further, here is what I found:

Sourdough is an old European method for collecting, keeping, and baking with yeast. Yeast occurs in many forms and species all over the place, including, apparently, the air around us. It is also found in the skins of wild grapes, and I imagine organic ones as well, and it is harmless. Yeast can be collected from the air using nothing more than a one-to-one mixture of flour and water in a jar with a cloth over it. If you set this out on your counter, yeast will collect in the mixture and grow and divide. Yeast divides rapidly, and while "budding" the process of dividing is a method of reproduction found in yeast, it is not the only one. In the process of growing and dividing, yeast gives off carbon dioxide and alcohol, hence the bubbles you will see in your yeast collector. Yeast is unique in that it is a single-celled organism that can break down complex carbohydrates, starches, and turn them into sugars for its own metabolism. The breaking down of these sugars is the cause of the CO2 and alcohol.

So what about the sour flavor? Sourdough starter is basically what results from this yeast collector. This mixture must be maintained every two or three days or so after it has started to cultivate the yeast, and this is done by removing a measure of the mixture and replacing it with fresh water/flour mixture for the yeast to consume, grow, and divide in. The mixture will also have a form of bacteria in it, lactobacilli, and this is for two reasons. The first is that bacteria is everywhere, and given the tools, it will grow. The second is that this particular form of bacteria can perform anaerobic respiration, creating energy for its use without oxygen, and the byproduct of this process is lactic acid. Why don't other forms of bacteria grow in this mixture and create a huge unsanitary mess? It turns out that this mixture is a very inhospitable environment for most everything except yeast and this bacteria, provided you provide fresh flour/water to feed it. This inhospitably is due to the alcohol, CO2 and lactic acid given off by the yeast and bacteria. So, not only can you collect yeast for baking bread straight out of the air, but a yeast collector is a terribly convenient arrangement for growing and storing it, without harm to you. Fancy huh?

Sourdough flavor then is the product of alcohol given off by yeast and lactic acid given off by lactobacilli. When used to make bread rise, sourdough starter gives its flavor over to the loaf. Do you taste a hint of sourdough in that ryebread you're eating? That might be because rye flour is often used for the sourdough starter mixture, and then to make rye bread. Whole wheat flour works as well.


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