How much slower is fridge fermentation?
Converted a ciabatta recipe to a sourdough recipe using a poolish
25 g active start
200 g bread flour
200 g water
Fermented 4 hrs at room temperature (73 F) and over night in the fridge. Poolish looked good this morning.
Added to poolish.
200g water
8g salt
300g bread flour
At room temperature I'd expect an additional 2.25-2.5 hours to fully ferment; expecting the bacteria to double (roughly) every 2 hrs. but I have work so I put it in the fridge.
Does anyone have an estimate for HOW much slower it will ferment in the fridge? Would it be ok for 9 hours? Or would it over ferment? Also when using these rough estimates for how fast the bacteria and yeast will grow, should you account for proofing as part of that time? Or add additional time for proofing?
Once temperature gets below 40F, yeast and bacteria will go dormant, hence no fermentation.
...but keep in mind that that's the temperature of the dough - so when you place your dough into the fridge, it's still warm enough to ferment for a while. It only stops when all of the dough has cooled down to fridge temperature.
At temperatures below 40F, fermentation continues. It slows way down, especially the yeast, which is near dormant, but not quite. Lactobacillus will dominate. You can expect the dough to exhaust itself in 6 to 7 days. Keep in mind that a starter kept in the fridge still needs to be fed, because the microorganisms are still active. You can observe a starter to peak and collapse in roughly 5 days, at which point you may choose to feed it.
I confirmed this by observation, and by referencing actual lab studies (it's been a long time and I've lost track of the actual study authors).
I've left dough in the refrigerator for longer than 6 days, and found it was flat and not responsive, while dough fermented in the fridge for 4 to 6 days proofs and bakes just fine.
One reference is here: https://www.weekendbakery.com/posts/a-few-tips-on-dough-temperature/ The graph shows that at 2-4C the curves for both yeast and LAB are near zero, the LAB is higher a bit, but neither is at zero. The graph was taken from the same study I tracked down, which was the state-of-the-art at the time, as far as I could tell.
I believe the actual study that produce the numbers behind the chart is this one: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3126363/ although the author names don't seem familiar and I don't see where they tested below 23C.
You can find references to the "master study" on this topic on this forum, and the authors were named.
I would suggest another look at what you had referenced. I will point out what you've missed:
First reference - below 40F, activity is so low it would hardly be noticeable in a real world situation - ie. The usual home baker isn't going to leave a dough in the fridge for a week or more.
Second reference is meaningless in regards to this thread as it only goes down to 73F.
So to answer one of the questions asked - 9 hrs in the fridge will not over ferment. And you proof until the dough is ready, however long it takes.
You can over-ferment in the fridge. 150 to 160 hours will do it, depending how you maintained your starter and on the inoculation percentage of your dough. I’ve confirmed it with regressions on the results from the original published study of LAB and yeast activity rates at various temperatures, and also experiments in my own kitchen. I think it’s a real world situation to ferment dough in the fridge, as many do it. Although not many know how long it can actually be left there.
I agree, 9 hours in the fridge isn’t enough to over-ferment.
And I now have answered the question: how much slower is fermentation in the fridge.