Bulk ferment vs cold ferment: two very common sourdough terms with two very different meanings.
Understanding the purpose of each period of fermentation is important to producing the best quality sourdough bread possible.
This blog explains what bulk fermentation is and why it's ideally not performed in the fridge, as opposed to the cold ferment, which is always done in the fridge.
If you need a quick overview of useful sourdough terminology, this sourdough glossary is really helpful.
What Is The Bulk Ferment and How Does It Work?
The bulk ferment or "first rise" as it's often referred to, is where all the sourdough magic happens.
The yeast in your sourdough starter feed on the food that you've given them (the flour and water) and produce C02 gas, which is what rises your bread.
Bulk fermentation should be done at room temperature - so you leave your dough on the counter for this part of the process.
Ideally, sourdough ferments best between 24C - 28C (75F-82F).
Bulk Fermentation Outside Ideal Temperatures
Sourdough will ferment at a range of temperatures outside of the ideals given above - the difference is the time it takes.
If you have an extremely hot or extremely cold home, you may want to look at a bread proofer.
If the ambient temperature in your home is outside of these parameters - bulk fermentation will still occur, however it may occur at a different rate.
For example, if your home is under 20C (68F) then you could leave your dough overnight on the counter for your bulk ferment (as long as you use the correct amount of sourdough starter).
If your home is above 28C (82F), then bulk fermentation will occur quite quickly and you'll need to watch your dough closely. It could be done in as little as 2 to 3 hours.
Here are some tips for making sourdough in hotter and colder temperatures.
At the end of your bulk ferment, your dough will be light and pillowy, full of bubbles and have doubled in size.
The surface of your dough will be slightly tacky, but not sticky.
There should be bubbles formed underneath which make your dough slightly wobbly to the touch.
You can see in the photo below that the dough is pulling away from the sides of the bowl.
The best advice I can give you in relation to bulk fermention is to watch your dough - not the clock!
Can You Bulk Ferment in the Refrigerator?
One of the most common misconceptions about the bulk ferment is that it can be done in the refrigerator.
In general, this is incorrect.
We can see from above that bulk fermentation requires a temperature above freezing - but ideally it needs to be above 4 degrees.
Anything under this will put your yeast to sleep.
Generally your fridge will be 4 degrees or below - making it way too cold for the yeast to happily work.
The only way you could do the bulk ferment in the refrigerator is if you left it there for a considerable amount of time - like between 3 and 7 days. Yes you read that correctly.
But this can have a detrimental effect on the gluten in your dough.
Bulk fermenting your dough in the fridge will take a very long time because the yeast are very sleepy at this temperature range.
This is why "overnight" bulk fermenting in the fridge never works - it will give you very under fermented dough.
The other problem with bulk fermenting your dough in the fridge is trying to shape a cold lump of dough.
Shaping is much easier when your dough is light and pillowy.
The moral of the story - keep your dough on the counter for bulk fermentation.
What is The Cold Ferment?
The cold ferment, or cold retard as it's often referred to, is the part of the sourdough process that occurs after shaping.
Once your dough is shaped and sitting happily in its banneton, it can go into the fridge for a rest - or cold ferment.
The cold ferment or cold retard occurs after the bulk ferment and shaping - it's not there to further “rise” your bread.
The cold ferment has the following purposes:
- development of sorudough flavour
- make it easier to score your bread
- allow you to put the yeast to sleep so that you can bake the bread at another time.
This is why it’s so important to get your bulk ferment right.
Extended cold fermentation will also give you a lovely blistered sourdough crust.
Will My Sourdough Rise During the Cold Ferment?
Now many people ask why their dough doesn't rise after being in the fridge for the cold ferment.
The simple answer is - it's not meant to.
I believe that some of this confusion has come from people referring to the cold ferment or cold retard as the “second rise” - this is incorrect.
If your fridge is 4 degrees or cooler (as it should be) the yeast will pretty much go to sleep (your bread may rise a teeny bit if you leave it in the fridge for a long time, like more than 24 hours), but in general it’s the bacteria that stay active during the cold retard.
If your bread rises too much in the fridge, you will risk it deflating when you score it.
The bacteria are responsible for the flavour in your bread, hence why a long cold ferment is a great idea if you like a more sour tasting sourdough.
The bacteria will produce acetic acid at very low temperatures.
Can You Skip The Cold Ferment?
Yes, you can skip the cold ferment. You cannot skip the bulk ferment.
If you bulk ferment your dough and then shape it - you do not have to put it in the fridge.
You could let it rest while you preheat the oven, score it and then bake it.
Of course, our ancestors did not have the luxury of a fridge to cold ferment their dough.
As above, cold fermentation lets us control the flavor of the dough, but also allows us to manipulate the process to fit into our busy lives.
Skipping the cold ferment may make your sourdough less sour or tangy.
Scoring may not be as easy if your dough is not cold, but if you don't want anything overly decorative, then scoring dough at room temperature will be absolutely fine.
Using The Freezer to Stop Over Proofing Your Dough
Your bread could also have risen in the first few hours of your cold ferment, while the dough is still cooling down and the yeast are active.
This is why it can be tricky to know when to put it in the fridge.
If you are sure your bread is heading towards being over fermented as it goes in the fridge for the cold ferment, it could be helpful to pop it in the freezer for an hour or so to really ensure that it drops the temp down and you’re not going to open the fridge to over fermented dough.
If you find that you’re putting nicely fermented dough into the fridge and it’s over-proofing while in the cold ferment stage, it’s really helpful to check the temp of your fridge to rule that out as an issue.
I hope this has helped you to understand bulk ferment vs cold ferment and why they are not interchangeable.
Frequently Asked Questions
Can you bulk ferment sourdough in the fridge?
No - bulk fermentation should ideally be undertaken at room temperature. The yeast and bacteria in your sourdough starter perform best in warmer temperatures so placing them in the fridge will put them into a sleepy state. It's much better to leave your dough to bulk ferment at room temperature and leave the fridge for cold fermentation.
Why doesn't my bread rise during cold fermentation?
Sourdough will not rise during cold fermentation if your fridge is set to 3-4C or lower. The yeast that rise your dough are put into a sleepy state once they enter these temperatures. Your dough may rise a little in the fridge but this will occur when the dough first enters the fridge and it is still cooling down. The yeast will still be active until the actual dough cools to 3-4C.
What's the difference between cold fermentation and cold retard?
Nothing. They are just different names for the same process.
Further Reading
If you enjoyed this article on the differences between bulk ferment and cold ferment, you might enjoy these ideas:
- Learn how to know when bulk fermentation has finished and it's time to shape.
- Learn more about cold proofing in the fridge and why it's beneficial.
- Autolyse vs Fermentolyse - learn what they are and when you should use them in sourdough baking.
- This article will help you diagnose your sourdough bread problems.
