By Tom Cucuzza, The Sourdough Journey © June 2023

What is the impact of feeding your starter different types of flour? 

I maintain my starter with daily feedings of a 50/50 mix of bread flour and whole wheat flour. In this example, I compared a 1:1:1 feeding of my starter with 100% Bread Flour, 100% Whole Wheat Flour and 100% Rye Flour. The results were surprising.

TIME TO PEAK – 12 to 14 hours (at 68F/20C)
The Whole Wheat flour got off to a very strong start, producing almost twice as much carbon dioxide as the Bread Flour and Rye Flour samples.

Whole Wheat peaked at 14 hours. Bread Flour and Rye peaked at 12 hours.

The Rye flour peaked at 12 hours with the lowest CO2 production at peak. Rye appeared to show a “false rise” with lots of bubbles and height, but low CO2 production.

CONVERGENCE at 23 Hours
At 23hours, Whole Wheat and Bread Flour converged. At 23 hours, the Bread Flour and Whole Wheat samples had generated 60% more CO2 than the Rye Flour sample.

TERMINUS at 36 Hours
At 36 hours, the Bread Flour had vastly outperformed the other two samples in total CO2 production. The Bread Flour sample produced 56% more CO2 than the Whole Wheat sample and 85% more CO2 than the Rye Flour sample. Whole Wheat produced 43% more total CO2 than the Rye Flour Sample.

ACIDITY (pH) MEASUREMENTS
There was no clear “break point” in the CO2 production related to the acidity (pH) of the samples.

SUMMARY
Whole Wheat gets off to a strong start, Bread Flour is a very strong finisher and Rye generally underperformed throughout.

Note: Starters created and maintained with each flour type may perform differently.

These results were surprising. I’ll likely run this test again to confirm, but there was no evidence of equipment problems or other external factors.