Interesting Sweet Stiff Levain pH data
If you read my blog here you may have noticed my use of sweet stiff levains (sugar added to the levain) for my enriched doughs in particular the Hokkaido milk bread. I had never bothered to measure pH of the dough or levains that I’ve made for this type of bread but decided I should check it today.
I’ve read, correctly or not, that using a sweet levain may encourage yeast growth over LAB. I’m not sure if that is correct of not but that is what I have read. Not being a microbiologist with access to a lab the one thing I can do with my baking gear is to measure pH and rise.
In theory, I think that if there is significant growth during fermentation of the levain that must indicate yeast population growth. Yes I am aware that LAB also produce some gas, but the yeast are the major producers of gas during fermentation and LAB are secondary. LAB on the other hand are the primary producers of acids during fermentation potentially producing both acetic and lactic acids.
So getting to the point I made a sweet stiff levain last night at this ratio 1:1.33:2.9:1 starter:water:flour:brown sugar. The pH immediately after mixing was 5.16. This morning after it had about a 3-3.5 x rise the pH was 5.00. I was quite surprised at the minimal fall in pH given the typical rise. This leads me to believe that the addition of sugar to the stiff levain does apply more negative pressure on the LAB than it does on the yeast given the excellent rise (gas production) and minimal pH drop (acid production).
In contrast I made a stiff levain without sugar using the same flour as the sweet levain, at the same time it had a pH of 5.37 after mixing and in the morning with a 3.5x rise it had a pH of 4.05 also typical for my stiff levains at peak when I use them.
Obviously I am unable to measure total titratable acid (TTA) as that would be the most accurate measure of the actual acid production. But given the huge difference it the delta pH drop I believe I can say that the addition of sugar does “seem” to encourage yeast reproduction over the LAB.
What do you think? Can you explain the difference in the delta pH of the two levains in another way?