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Sourdough for Science: Part 4: How to pick the best sourdough starters

February 21, 2019

By special guest blogger Erin McKenney, MS, PhD

On Friday, February 15, the students entered their 10th day of data, gathered their supplies, and voted to select the best starter grown from each type of flour. The six best starters from each school would be baked into loaves at Boulted Bread for a taste test on Tuesday. But how to pick the best starters?

We first identified which starters had the lowest pH (3.0–3.5, instead of 4.0) and created the most carbon dioxide (as measured by the number of bubbles per cm2 and the total height that the starter grew). These traits indicate the microbial functions you would expect in a mature sourdough starter: bacteria create lactic acid or acetic acid, which lower the pH; and yeasts create carbon dioxide, which forms bubbles and makes the starter rise. The starters with the lowest pH and the most carbon dioxide are therefore most likely to have reached a climax community.

If two or more starters were “tied” for pH and carbon dioxide, we next looked for consistency over time (which, again, indicates a stable climax community) and also compared the smells of each starter. Smell has been an important food factor for humans for millennia: microbes that make us sick tend to create smells that we don’t find appetizing. No one wants to eat something that smells rotten, even if we don’t know which microbes might be making that smell.

Now that the best starters have been chosen, I’ll take care of them over the weekend. Boulted Bread will mix them into bread dough on Monday, and bake loaves for the students to taste test Tuesday morning!


The box full of starters. Photo: Erin McKenney.

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