Cold bulk fermentation has been my go-to bread making method lately. It is convenient, easy, and the resulting bread has a far superior flavour. Usually, I leave the dough to ferment for 12 – 24 hours because it produces a great result, and I don’t want to plan my bakes too far ahead of time. And although my fridge is usually quite empty it does fill up occasionally and I can’t afford to take up any more space in it.
There are many recipes out there (usually for pizza dough) which suggest cold fermenting for several days. This got me thinking as to how long we can ferment bread dough in the fridge and how fermentation time affects the resulting bread.
First off let’s get one thing out the way – the effects and the results of long cold fermentation will vastly differ between commercial yeast dough and sourdough. This test was performed with commercial yeast fermented dough. While both share similarities, the slow fermentation effects on sourdough bread will be far greater than on yeast dough because a sourdough starter is a culture containing multiple yeasts and high concentrations of acid bacteria which affect the taste more than commercial yeast is able to.
There are two main characteristics of dough that get affected by fermentation – flavour and gluten structure. The longer the fermentation the more intense the taste of the bread. And the longer the fermentation the looser the gluten structure becomes as a result of increased acidity.
Respiration and fermentation.
Respiration is the production of CO2 and water by the yeast. Amylase enzymes in the flour process starch and convert it to simple sugars which the yeast consumes. The by-products of this process are carbon dioxide gas and water. It is the gas that builds up inside the dough and makes it rise.
The greatest amount of gas production happens at higher fermentation temperatures. Think of oven spring. While the dough can gain a larger volume during a short time, it will not develop that much flavour.
Alcoholic fermentation occurs at lower temperatures and in the absence of oxygen. During this process the yeast produces carbon dioxide and alcohol (ethanol). Bacteria and acids are also produced. They are responsible for flavour and structure development.
Starch will break down in a moist and acidic environment through a process called hydrolysis. It is the acids that continue processing the starch while the amylase enzymes slow down at colder temperatures.
Even though CO2 production slows down, fermentation is continuing. Aside from respiration, yeast dough can ferment with lactic acid and acetic acid bacteria as over time the bacteria multiply.
This is a characteristic more well known in the process of sourdough bread production. In yeast dough it has the greatest effect only at low temperature fermentation.
Organic acids affect the dough in a few interesting ways. They lower the pH making the dough more acidic, they produce a more intense flavour, help with gas production, make the dough more extensible, strengthen the gluten structure and help the dough retain more gas. And as we all know cold and slow fermented breads stay fresher for longer too.
Alcohol (ethanol) improves the smell, flavour and keeping quality of the dough. Most of it evaporates during baking, but some will always remain. Saying that, your bread should not smell much of alcohol. If it does, then it was most likely over proofed.
Lactic acid bacteria (LAB) lower the acidity of the dough. Both commercial yeast and sourdough prefer slightly more acidic environments. pH 4.5 – 6.5 is normal for commercial yeast bread doughs while sourdough can drop close to pH 3.0. When the dough becomes too acidic yeast activity slows down considerably the gluten starts degrading.
When dough is cold fermented its temperature drops down so low that the yeast becomes dormant. While the yeast is in a slumber, sugars are still being produced through hydrolysis. These sugars remain in the dough unfermented until the temperature starts increasing after the dough is taken from the fridge and left to proof, or when it is baked directly from the fridge.
As soon as the temperature increases the yeast will start rapidly consuming the sugars and multiplying at an accelerated rate. This will make the dough fill up with CO2 and rise during the final proof or result in oven spring when baked directly from the fridge.
As the yeast dies off at around 60C (140F) the remaining sugars in the dough will leave it tasting sweeter and will make the crust caramelize and create a richer colour.
In short – respiration is responsible for volume while fermentation is responsible for flavour. It is the balance between the two that gives the bread its volume and flavour.
The tests and results.
I made 4 breads. One was fermented for 14 days, another for 7 days, another for 5days, and the last one for 2 days. The idea was the find out how the dough changes over time and how the resulting breads differ from each other.
All doughs contained 200g white bread flour, 20g whole wheat flour, 4g salt, 150g water. Both the 14 day and 7 day fermented doughs had 0.5g yeast. The 7 day fermented dough had 0.7g yeast and the 2 day fermented dough had 1.5g yeast.
They were all mixed and left to ferment without kneading or folding.
The 14 day fermented dough reached its peak in 5 days and collapsed. It then rose back up the following two days and collapsed once again. After the second time collapsing it did not rise back up to the previous level. It kept reducing in volume and changing colour.
The 7 day fermented dough also reached its peak in 5 days, then collapsed and rose back up until day number 7. It behaved the same as the 14 day fermented dough up until that point because the recipes of both of them were identical.
The 5 day fermented dough contained more yeast to account for the shorter fermentation time. It had reached its peak and started to try and escape the container during day number 5.
The 2 day fermented dough contained even more yeast and it rose to almost its peak in the two days.
I baked the loaves in pairs a couple hours apart because I only have two of the same sized tins that these doughs can fit in. The 14 and 7 day breads were baked together and the 5 and 2 day were baked later.
All doughs were extremely stretchy and loose, but there was clear progression between them with the oldest being the loosest. Pulling the 14 day fermented dough made it tear extremely easily. That is the gluten degradation due to acidity. While I don’t have a pH meter I am pretty sure it must have been below 3.
The other doughs tore relatively easily too, but they were not as fragile as the 14 day one. Keep in mind that I did not knead or fold any of them.
They all had a bit of an acidic alcoholic smell, but the 14 day dough smelled far stronger than the others. There was not a big difference between 2 day and 5 day. There was however a bigger difference in the 7 day and 2 day fermented dough smell.
Even though all of the doughs were loose and weak, with some tighter shaping, stitching, and repeat shaping, they were all able to be turned into strong enough loaves. Even the 14 day fermented dough was able to retain some gas.
When it came to volume and oven spring the 14 day fermented dough was the smallest and gained the least as expected by now. The other three performed similarly to each other.
Smelling the breads after baking revealed a progression in acidic smell up until the 2 day fermented bread. The oldest had the strongest smell and it decreased down the line. There was not a great difference in smell between the 5 and 2 day fermented breads.
Taste and texture wise 14 days produced a loaf with a higher acidity which also tasted very sweet. It had an extremely moist and chewy crumb and a very crispy crust.
The 7 day ferment produced a loaf that was not as acidic and not as sweet. It was a lot lighter and had a thinner crust.
The 5 day ferment resulted in an even milder loaf although it would have been hard to tell the difference between it and the 7 day ferment in a blind taste test.
The 2 day fermented loaf had the mildest taste, softest crumb and thinnest crust of all.
When comparing the 7 & 5 or 5 & 2 day fermented breads to each other there was not a huge difference. Only when comparing 7 & 2 I could tell them apart in a blind test.
However, the 14 day fermented dough was in a league of its own. It had a very unique taste and texture. It could not produce a tall loaf, but it could make a nice pizza I imagine. It would be quite chewy though.
You can ferment your bread dough in the fridge for as long as you want. I’m not sure at which point it would turn into an unusable goop, but it will take more than two weeks for sure. Taste is highly subjective and I can’t tell you how long to ferment your bread for maximum flavour. For me, the two week fermented bread tasted nice and I would not mind eating it. For you it may be totally disgusting.
Watch the video here