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Sourdough for Science: Part 2

February 8, 2019

By special guest blogger Erin McKenney, MS, PhD

This rye starter was active that the overflow soaked and burst through its paper towel cover. (Photo: April Shoemaker, Ligon middle school.)

This rye starter was so active that the overflow soaked and burst through its paper towel cover. (Photo: April Shoemaker, Ligon middle school.)

On day three of the experiment, students at each school arrived to discover that some of their sourdough starters had overflowed their jars! Hyper-activity is common in the early days of sourdough starter growth: the flour-and-water mixture does very little the first two days, and then on the third day it explodes… only to settle back down for a few more days. This is one of many “typical behaviors” that is common across sourdough starters, but that no one has formally studied before.

Personally, I think it is a natural part of colonization (also known as succession, the ecological process by which a community grows and changes over time).

About Succession

When communities grow “from scratch”, different species join the community and grow in predictable patterns known as succession. Pioneer species are the first “colonizers” to arrive. They usually grow very quickly (“like weeds”) and take over the ecosystem for a short period of time. But in the process they consume readily available resources and change the environment to favor slower-growing, more permanent community members.

Example: Field to Forest
Exhibit: From Forest to Field and Back Again

In the “Mountains to the Sea” exhibit, this panel shows how communities of plants and animals become re-established after a disturbance in a predictable order. Photo: Karen Swain/NCMNS.

In the plant world, weeds eventually give way to shrubs, pine trees, and finally a hardwood forest. This forest is called the climax community.

Sourdough Succession

In sourdough starters, the flour provides plenty of food (i.e. sugar and starch) for the microbes but it takes a couple of days for bacteria and yeast to colonize the mixture and really start to grow. (The “explosion” of sourdough on the third day happens because that’s how long it takes for the first “microbial weeds” to grow.) In the baking world you hear about the overflow phenomenon most often with rye flour.

In fact, bakers recommend creating a sourdough starter with rye because it “jump starts” the growth of the starter.

Why would this happen?

I think this is because rye contains more starch than wheat. It’s like a sugar rush that makes the microbes hyperactive.

So it wasn’t a big surprise when teachers reported on day three that their rye starters had overflowed. The bigger surprise came today: now the millet starters have exploded! This suggests that succession occurs at different rates, depending on what type of flour (and nutrients in that flour) you feed to the starter.

Even more interesting is that all-purpose starters aren’t doing much at any of the schools… unless, of course, they’re just gearing up to overflow tomorrow… Only time will tell!

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