The Fresh Loaf

News & Information for Amateur Bakers and Artisan Bread Enthusiasts

How starter hydration slows bacterial fermentation

Chausiubao's picture

How starter hydration slows bacterial fermentation

 Since school there was one nugget of sourdough wisdom that had always been drilled into me, “firm starters produce acetic acid and liquid starters produce lactic acid”, the lesson continues that breads made from the appropriate starter will also produce breads of following acidity, with lactic acid being the weaker of the two. Yet, recent discussions of the topic point to the opposite, which does make some sense, with less water to move around in, bacteria would be less able to access appropriate nutrients, therefore, energy, with which to grow and reproduce. So the by-product of their existence, acid, would be lower in quantity, regardless of the relative strength of their specific acid. 

 Two of Hamelman's sourdough formulas, the “Vermont Sourdough” and his, “Pain au Levain” are virtually identical but for two procedural discrepancies, the Vermont Sourdough uses a 125% hydration starter and is retarded for the final proof, whereas the latter utilizes a 60% hydration starter and has absolutely no retarded fermentation whatsoever. This being the perfect experimental set up for proving the truth of this question to myself, I decided to mix these two formulas, and conclusions come what may.

The main question here could be summarized as, “What differing flavor profiles are a result of extending the bacterial fermentation compared to relatively limiting their growth?” A secondary question was, “What is the optimal final proof time of a sourdough loaf?”

Vermont Sourdough

90% Bread Flour

10% Rye Flour

67% Water

1.9% Salt

15% Pre-fermented Flour

Pain au Levain

95% Bread Flour

5% Rye Flour

67% Water

1.8% Salt

15.5% Pre-fermented Flour

Both doughs were mixed to an improved window and medium soft consistency. They were also both bulk fermented for approximately 3 hours with a single fold at 90 minutes. After shaping, the procedure diverges when the Vermont Sourdough is retarded overnight and the Pain au Levain is not. The loadings of both doughs were staggered, with the first half of the batch being loaded when I felt it was appropriate, the second set, after that.




Interestingly enough, neither dough was particularly acidic. The Vermont Sourdough had some acidity on the back end with particular emphasis on the after taste, but not unpleasantly so. Comparatively the Pain au Levain had no discernible acidity. Despite the rumor that naturally leavened breads are sour, this was an exception to the rule. In both cases the oven spring was greater then desired. This was true in both the first and second loadings of both doughs. Even at a three hour final proof, there was excessive oven spring. There may have been complications with the shaping of the loaves exacerbating any underproofing here; but the second loadings had less spring then the first sets.




Dough fermented with a liquid starter and retarded overnight produced a more acidic flavor then a dough fermented with a firm starter and no retarded fermentation. This much is clear, which of these two variables contributed more to the acidity is still uncertain. This with a longer final proof will have to be explored next time!


pmccool's picture

but I don't see that you've nailed down the question of which style starter produces which flavor profile.  As long as the two doughs have such different proofing regimens, there's no way to isolate for the effect of the starter hydration.  It seems that you would need to conduct two bakes; one where both doughs are fermented at room temperature and another where both are retarded in the refrigerator.  Even then you won't be able to entirely discount the effect of the fermentation process but you will at least be comparing like to like.

I suppose if one were to be really rigorous, you'd have to make the same formula using the two different types of starter rather than two somewhat different formulae.

Since you are committed to seeking and I am merely curious, I'll get out of the way while you carry on with experimenting. '-)


Chausiubao's picture

Certainly certainly, my results are certainly unclear. I think the part that stood out the most was that the pain au levain that received no retardation, had no acidity.

But, I continue on! I'm planning on feeling my way through this question as I go.

Until the next installment,


varda's picture

This is an area I have found totally opaque, no matter how much I read, perhaps because as you say, you see things on both sides of the argument.   I recently posted on a formula where I baked one loaf same day and the second from the same liquid starter formula on the second day.    The tastes were almost identical, however with the retarded loaf with a very faint taste of sour.   So my "experiment" looked at only one variable for sour - overnight retardation vs not - while keeping hydration of the starter (and the loaves) identical.    I was quite surprised to taste so little difference.   I'm very interested to see your results going forward.  -Varda

Mini Oven's picture
Mini Oven

but I bet I could taste which one contained more rye %!  And whether it was fermented longer.   Any takers?

Yerffej's picture

A worthwhile post and I must agree with Paul's comments that there are too many variables here to know exactly what is causing what. 

I have made firm starter doughs with all things being equal except that I baked half  on day one and the other half on day 2 after cold bulk retardation.  I did not detect a difference in the degree of sour but the flavor difference was of night and day proportions with the day 2 loaves being infinitely superior to the day 1 loaves.

And Mini.........No way am I betting against your taste buds,



jcking's picture

Temperature? Curious as to the DDT and bulk ferment temperature?


Chausiubao's picture

What is DDT? I'm not familiar with that abbreviation. As for the bulk ferment temperatures, they were both in the low 70s, I can't recall (nor have I records, past the feeling of satisfaction in knowing they were satisfactory if a bit cold).

In either case, the take home point is that the fermentation temperature was acceptable, if below optimum.

jcking's picture

DDT is desired dough temperature reached at the end of mixing. It can be searched here and is explained in Hamelmans book. Three things to measure/record when evaluating the results of the baking process are time, temperature and hydration. Temperature is measured beginning with ingredients and ending with the finished loaf. Temperature is as important of a factor as time so including temperature factors will result in a more accurate picture of the process. Different fermentation and proofing temperatures will affect yeast and bacterial growth.


Chausiubao's picture

Ah, well in that case i was aiming for ~75 F, but got 70-72F for the most part.