cold bulk fermentation is a serious game changer

I’m kicking myself. Why have I not cold bulk fermented earlier?! Not only does it boost flavour, it’s also a lot more convenient.

Typically I take 3–4 hours to bake a bread, starting any time between early afternoon and early evening, which means that it’s late afternoon or late evening by the time it’s done. The time it takes isn’t a problem—3–4 hours is really fast compared to most bakes. The problem is that I would have to dedicate a chunk of my day being confined to my apartment. In lockdown this wasn’t a problem, but beyond that, there have been times when I’ve had to skip social engagements because I was in the middle of baking and couldn’t leave the dough unattended.

Even if you didn’t have plans to go out, the downside of finishing bread late in the evening is that you would be in bed before you could sink your teeth into it. Not being able to enjoy fresh bread out of the oven is one of the cardinal sins of baking, alongside eyeballing ingredients and blindly following proofing times. It also doesn’t make a lot of sense to go through all that effort of baking your own bread just to enjoy half-day-old bread the next morning.

Another problem I experienced over the summer was that the dough would ferment too quickly at room temp.

What is fermentation?

Fermentation is the process whereby yeast eat the sugars present in the dough, and then poop out carbon dioxide gas and alcohol. These gasses that are released are then trapped by the elastic strands of the gluten network you’ve developed through kneading and the autolyse process. The trapped gasses—or yeast farts—are what causes your dough to rise, and they result in the little holes you see in a slice of bread.

What is bulk fermentation?

Bulk fermentation refers to the process after kneading when you let the dough rise for the first time. In a commercial setting, bakers would start with a big batch of dough that would later be separated into smaller portions, hence the term “bulk”. In my case, as is the case for many home bakers, I won’t be dividing my dough into smaller portions. For this reason, bulk fermentation is also known as the initial/first rise or fermentation or proof.

On hot days in my kitchen, bulk fermentation or the initial rise would take around an hour, which is too little time for flavours to really develop. Conversely, longer fermentation allows for the development of more complex flavours, as well as better texture.

Yeast thrive in warm temperatures. This is because the enzymes, or proteins that catalyse chemical reactions, within the yeast perform optimally around 37°C—which interestingly is the same temperature for a functioning, healthy human body (though recent research suggests that this figure has been falling).

The two main enzymes found in yeast are maltase and invertase, which are both disaccharides (double sugar). Maltase causes the chemical breakdown of maltose (a sugar produced by the breakdown of starch) into glucose (a simple sugar). Invertase causes the chemical breakdown of sucrose into glucose and fructose (another simple sugar, naturally found in fruit, honey, agave, etc.). So at warm temperatures, the enzymes break down double sugars (disaccharides) into simple or single sugars (monosaccharides) for the yeast to eat.

Cold bulk fermentation

To slow down this process and allow for more flavour development, we need to reduce the temperature. This is why we bulk ferment the dough in the fridge instead of leaving it on the bench. At lower temperatures, the enzymes’ ability to catalyse the chemical reaction or breakdown of sugar is minimised, meaning that the yeast don’t have as much sugar to feed on and therefore don’t release as much gas to make the dough rise.

Here’s how I CBF’d.

First, some bread stats:

Whole wheat, 85% hydration
– 390g Weizenvollkornmehl/whole wheat flour, 13% protein
– 4g dry yeast
– 330g water
– 9g salt

Start at 20:00. Or roughly 12 hours before you plan to wake up the next day. As usual, mix all ingredients, autolyse for about 15 minutes, knead away, then cover and place in fridge, along with small sample dough to measure the rise.

And that’s it! I mean, for the first part. About 30 minutes of work in the evening, then you whack it in the fridge and completely forget about it until morning, letting it do it’s slow ferment thing while you sleep. Too easy.

The next day

Morning comes around, take the dough out of the fridge at 08:00. It’s had 12 hours to ferment. I give it a coil fold to bring it back into shape. Now, this depends on how cold your fridge is, but when I took out the dough it had increased about 75% in volume. I was looking to go double in size, so I let it sit on the bench for about another hour to continue fermenting. I give it another coil fold 30 minutes in.

While the dough is completing its bulk ferment on the bench, I turn on my oven to ensure that it is has enough time to heat up and set up the water bath for steam. Once the hour is up, I check on the sample and it’s nearly doubled in size. Decide it’s good to go, and I proceed with shaping before placing it into an unlined banneton for the second proof, which takes around 15 minutes to pass the poke test.

By this time the oven is piping hot. I carefully take out my pizza stone, sprinkle semolina flour on the dough while its still in the banneton, then flip it over out onto the stone. I quickly proceed to score the loaf, which is so much easier, as the dough is colder and therefore holds its shape better. The whole wheat also helps, as it absorbs way more water, giving me a more stable, less jiggly dough.

The dough gets a few spritzes of water before I hastily slide it into the oven, sneaking in a couple more spritzes for good measure before closing the door. After 30 minutes I remove the water bath and top tray that acted as a dutch oven lid, and let the bread bake for a further 10–20 minutes, depending on how dark I want the crust.

I think this has been my best one to date.

Check out that oven spring. A Breakfast Club-style fist shoots upwards before retracting to wipe proud tears from the eyes of someone recalling all the failed attempts, all the flat discs. And now, finally, I’ve nailed the fermentation time and oven temp. The spring is on point. I also need to attribute some of that success to the higher protein content. The particular flour I got, from Kaufland, has a protein content of 13%, compared to the 10–12% I usually see. This means there is more gluten, which makes the dough more elastic, allowing it to expand in the oven.

Also very happy with the bottom crust. I was having trouble with this for the longest time. At some point I even looked up different qualities of baking paper and how they could be trapping moisture underneath—which was why I didn’t use any this time ’round, riskily flipping the dough from the banneton straight onto the stone instead. But I think what truly made a difference was turning my oven all the way up and getting the stone nice and hot to sear the bottom of the dough. I think next time I might try turning on the oven well before baking and using the baking paper, and see how that turns out.

The bread was soft with a good chew. Texture 8/10. I reckon I could push the hydration a little bit more next time, to 90% maybe. It’s whole wheat, it can take it. Flavour was great, mainly owing to the fact that this was whole wheat, but also due to the longer ferment. Overall, extremely happy with this one!

Yeast out,
Jen