Building a Proofing Box from a Tote and Heat Mat
Okay. Last lesson we talked about reading your dough instead of the clock. This lesson is about giving that dough a stable place to sit while you're doing your reading.
Here's the problem. Most houses have a spot that's warm-ish and a spot that's cold-ish, and neither one is consistent. Your kitchen might be 68 degrees in the morning and 74 by afternoon once the sun hits it. Set your dough near a heat vent and one side of the bowl proofs faster than the other. Set it on the counter in January with the furnace cycling on and off and you're proofing at whatever temperature the house feels like giving you that hour. None of that is dough's fault. It's an environment problem, and environment problems have environment solutions.
I fix mine with a plastic tote and a seedling heat mat, and it's genuinely one of my favorite things I've built for this whole process, because it's cheap, it's dumb simple, and it works every single winter.
What you need
- A clear plastic storage tote, the kind you'd get for under-bed storage. Mine's a 30-quart size, big enough to fit a mixing bowl and a banneton at the same time.
- A seedling heat mat. These are made for starting garden seeds and you can find them at a garden center or hardware store, usually 20 to 25 dollars. Look for one with a low, steady wattage, not a space-heater situation.
- An oven-safe thermometer or a cheap digital probe thermometer, something you can leave inside to actually read the temperature instead of guessing.
- A small dish of water to sit in the bottom, for humidity.
Building it
Lay the heat mat flat on the counter first, then set the tote upside down over it, or right side up with the mat underneath the tote floor. I've done both. What matters is the mat is making contact with the tote and not folded or bunched up, because a bunched mat gives you a hot spot instead of even heat.
Plug it in and let it run for about twenty minutes with the thermometer inside and the lid mostly on, cracked maybe an inch for airflow. Check the number. You're aiming for somewhere around 78 to 82 degrees inside the box. That's warmer than your kitchen, plenty warm for bulk ferment or a final proof, and it's a number that stays put whether it's snowing outside or not.
If it's running hotter than that, prop the lid open a little more. If it's not getting warm enough, check that the mat's actually contacting the tote and not just sitting loose underneath a wire rack or something. Some totes are thick enough to insulate too well against the mat. Thinner-walled totes transfer heat better, which surprised me the first time I built one of these.
Add the little dish of water in the bottom corner. Our air here is dry enough that an uncovered dough can crust over before it even finishes proofing, and a crusted skin on your loaf will fight you when you try to score it later. The water dish keeps humidity up inside the box so that doesn't happen.
Using it
Once it's dialed in, I put the bowl of dough right inside, lid cracked, and I mostly forget about the fussing and go do something else. That's really the point. I built this thing because I know myself. I want to rush bulk ferment, I've done it before, and this box takes some of that decision out of my hands. I set the dough in, I set a timer, and I go poke at the dough by feel like we talked about last time, not by staring at a clock on the wall.
I measured mine when I built it, leveled the tote so it wasn't rocking on the counter, and labeled the mat's control dial with a sharpie mark for where I like it set for bread versus where I had it set the one time I tried to sprout seeds in there instead. That's just how my brain works. If you're the same way, do that. If you're not, fine, just get the temperature dialed in once and leave it alone.
One opinion here, since it comes up in class: I'd rather you pull dough a little under-proofed out of this box than let it go too long chasing that big airy crumb everybody wants. A slightly under-fermented loaf still slices fine and tastes good. An over-fermented one goes slack and gummy and there's no fixing it once you're there. The box helps with consistency, but it doesn't replace watching the dough.
A caution worth saying plainly: these heat mats are low wattage, but they're still an electrical thing sitting near a water dish, so keep the connections dry and don't let the dish overflow onto the mat itself. And don't leave it running unattended for hours at a time the first few uses, until you know how your particular setup holds its temperature.
Before next time
If you've got a spare tote and can grab a heat mat this week, build one and get it dialed to 80 degrees before our next class. If not, no worries, we'll have a couple in the room you can borrow and copy.