Jim Carson

Last week, I wrote about the difficulty I had getting my sourdough starter ... started. All this effort is done because I want to have a starter that leavens and provides a rich flavor in my bread.

Leavening in baking is done aerating the dough with carbon dioxide, causing it to puff out. There are four common ways to do this:

1. Baking soda, also known as sodium bicarbonate (NaCO₂), is an alkaline substance which, when combined with an acid, creates carbon dioxide gas and salt. (It also releases carbon dioxide when heated above 50°C.) Mixing baking soda and vinegar in a makeshift "volcano" entertains young children for hours at a time.
2. Baking powder is a combination of baking soda and an acid such as calcium acid phosphate, sodium aluminum sulfate, or cream of tartar. When water is added, the acid and alkalines mix, forming carbon dioxide. There are three kinds of baking powder, but double acting is one you'll find in the grocery store. The "double acting" refers to its leavening on contact with moisture, and during baking.
3. Baker's yeast -- saccharomyces cerevisiae is widely used because it provides quick rising. It's also popular with genome analysts.
4. Wild yeast -- yeasts in the environment and flour. In sourdough bread, this is often candida milleri (and others), which is more tolerant of an acidic environment. More on that later.

Yeast works by consuming sugars in flour and producing carbon dioxide and alcohol. Initially, yeast prefer to consume simple sugars such as glucose and fructose. The chemical reaction might look like this:

Yeast	+	sugar	=	alcohol	+	carbon dioxide
		C6H12O6		2 x CH3CH2OH	+	2 x CO2
		glucose		ethanol

Yes, hooch. S.cerevisae can produce 15-16% ethanol by volume. The "hooch" evaporates during the first few minutes of cooking. The yeast themselves are killed by the cooking process. (Yeast die when in temperatures greater than 130°F.)

If all we were interested in was the leavening, we could use commercial baker's yeast and be done with it. Quickly. What makes sourdough unique, time-consuming and old-fashioned, is its reliance on a symbiotic relationship between the wild yeast and (lactic acid) bacteria: yeast provide the leavening, bacteria provide the flavor.

When I built my starter, I started with dried starter and whatever yeasts and bacteria were in the flour, air and water at the time of hydration. The heating and constant churn of the starter is done to support growth of the desired organisms, the wild yeast and Lactobacilli bacteria (which I'll refer to as "lactobacilli"), giving them time to establish. The relationship between them is complex. Starter formation takes such a long time because we're trying to establish the lactobacilli that grow slower than the yeast. When lactobacilli eat the sugars in flour and dead yeast cells, they produce lactic acid, which gives sourdough its characteristic flavor. The acidic environment also acts as an antibiotic to thwart other yeasts and bacteria from establishing themselves in the starter. This is why you can leave starter sitting out on the counter.

When a starter is established, there's a balance between the bacteria and the yeast. As long as is not overheated, starved or poisoned, it will maintain itself.

Kalamata olive bread - version 1.0
adapted from Peter Reinhardt's excellent Bread Baker's Apprentice, p. 135
1/2 C sourdough starter
1 C flour
1/2 C warm water

1 1/4 C water (approximately)
3 1/4 C unbleached flour
1 1/2 T kosher salt
1 1/4 C kalamata olives, pitted and cut in half

1. The night before making the bread, mix the starter, flour and water in a cup. Cover, and place on the counter at room temperature (70°F). Let rise for about 18 hours, or until doubled. This should rise very slowly.
2. The next day, mix the flour, water, sourdough starter and salt into a ball. I recommend doing this with a KitchenAid mixer and a dough hook. Use a spatula to help keep the stuff off the sides until the ball is formed. If the dough's too dry, add a small amount (1T) of water and mix another minute until the ball is largely established. If the dough's too sticky, add a small amount (1/8 C) of flour, and do the same. The dough should be kneaded in the mixer for about 15 minutes total, but it won't hurt if you do it more.
3. Stir in the olives and mix for another minute, just enough to distribute the olives evenly. You don't want to do it too much otherwise the dough looks funky black purple.
4. Cover and let rest 20 minutes. I find it helpful to spray a small amount of Pam-equivalent on the bottom of the bowl to facilitate non-stickiness.
5. Turn the dough by hand. Cover and let rest 20 more minutes.
6. Turn the dough by hand. Cover and let rest 20 more minutes.
7. Turn the dough by hand. Cover and let rise until doubled, about 3-4 hours, less if it's warmer.
8. Put a small pan of water in the oven and preheat the oven to 425°F. Gently place the risen dough on a piece of parchment paper.
9. Cook the bread for about 20 minutes, rotate it 180°, then cook another 20 minutes. The bread will have a nice crisp, brown crust, and will sound hollow when thumped.
10. Cool on a wire rack. Enjoy