A Slice of Bread as a Yogurt Starter?

Venezuelan fermentation enthusiast Neyda Fernández wanted to make yogurt but was having trouble finding a starter. So she decided to experiment with a method she had heard about, using a slice of bread as a starter.

Here is her write-up of the experiment and her results:

Making yogurt from a slice of bread

Question: Is it possible to make yogurt using a slice of bread with some milk as a starter culture?

Motivation: Allow people who live in countries – like my hometown, Venezuela – where it’s not easy to find ferments like natural unsweetened yogurt to make homemade yogurt using as a starter a slice of bread, an easy and common ingredient.

Hypothesis: There are enough lactic acid bacteria in bread to use it as a ferment to make yogurt. Probably they are not the same strains present in commercial yogurts but they will produce enough lactic acid from lactose to acidify the milk.

Procedure/Recipe: Put a piece of bread in a small bowl of milk for 24 hours to 48 hours, depending on the ambient temperature, then discard the bread and use the curdle as a starter culture. From this point I used the yogurt recipe from “Food Fermentation: The Science of Cooking with Microbes” course.

Control: Just milk
Variables: Milk and a slice of bread white bread (Wonder); Milk and a slice of baguette
Type of milk: Dairy
Measurement tool: pH strips

In each batch, the milk’s starting pH was 7. A starter was prepared by keeping the milk and bread (or without bread in control) at 28 degrees C (82.5 degrees F) for 24 hours; then yogurt was prepared with using that starter, incubated at 43 degrees C (110 degrees F) for 8 hours.

Control (milk only) starter, with a pH of 7, was not sour, and curdled slightly. The incubated yogurt it produced had a pH of 6. “Sweet like milk, sourness undetectable.”

Baguette starter was slightly sour, with a pH of 5, and curdled. The incubated yogurt was creamy, semi-solid, and slightly sour, with a pH of ~4. “Even though I liked it,
it was too sour.”

White Bread (Wonder) starter was also slightly sour, with a pH of 5, and curdled. The incubated yogurt was creamy, semi-solid, and slightly sour, with a pH of ~4. “This was my favorite,tastes close to commercial yogurts.”

Conclusion: The hypothesis is correct, there are enough lactic acid bacteria in a loaf of bread to use it as a starter culture to make homemade yogurt.

Update: Neyda writes “Great news! I did the backslopping method and it worked!!! I have made five batches so far and the texture is as good as the first one.”