Back in stock! Gentle warmth. No complicated settings. Cold kitchen? Winter sluggishness slowing your starter or dough to a crawl? This is the fix — and it won't cost you $95. Most proofing boxes are bulky, expensive and packed with dials you'll rarely use. Ours is the opposite. At just $34.95, it’s a simple and affordable way to create a gentle, stable environment to support healthy fermentation—especially during cooler weather. There are no settings to adjust or temperatures to monitor. USB power means you can run it from a laptop, wall plug, or power bank. When you're done, it folds flat and slides into a drawer. And because it's so light, your starter doesn't have to skip a feed when you travel. Affordable, foldable, transportable — and built to actually fit our sourdough mixing bowls. What's included: Foldable heat proofing box, foil-lined USB cable Low-wattage heat mat for gentle even heat distribution Specs: Power: USB (5V2A)— works with USB-A chargers and USB-A power banks Heat output: one constant optimal temperature made for sourdough fermentation Folded size: 32.5cm x 30.5cm x 3.5cm thick Open size: 32cm x 30cm x 20.5cm height Weight: 200g Please note: You will need a USB-A power source (such as a wall plug, power bank or laptop) with a minimum output of 5 volts and 2 amps. Some older USB power adapters may provide less than 2 amps and will not supply enough power for the unit to operate correctly. How does the box work? The heat box maintains a gentle fermentation environment of between 21-28°C, with the internal temperature varying slightly depending on the ambient room temperature and the amount of starter or dough inside. Please note: If the surrounding environment is particularly cold, or if you’re fermenting a larger quantity of starter or dough, the temperature inside the box may be slightly lower. This is completely normal, as the heat box is designed to provide gentle, gradual warming rather than direct heating. Here's the simple routine: 1. Plug it in Connect the USB cable to a power bank, USB wall adapter, or any compatible USB power source. The box will gradually warm to steady range between 21-28°C. The time and temperature will vary depending on your room temperature and the amount of starter or dough inside. 2. Place your starter jar or dough inside Place your starter jar or dough into the box. If you're using our Sourdough Mate Starter Jar, remove the silicone seal to allow carbon dioxide to escape during fermentation. If you're using a standard jar, keep the lid loosely fitted or only lightly screwed on. Pro tip: Place a small cooling rack inside the heat box to keep your starter or dough slightly elevated above the heating pad. This helps distribute the warmth more evenly for consistent fermentation. 3. For best results, keep the box closed during use To maintain a consistent temperature, avoid opening the box unnecessarily while your starter or dough is fermenting. Each time the box is opened, warm air escapes and the internal temperature can fluctuate, which may extend fermentation times. Of course, you can check on your starter when needed, but frequent opening may slow the warming process and reduce temperature stability. If you'd like to lower the temperature slightly, simply leave the zip partially open to allow a small amount of heat to escape. 4. Check after 3 hours (earlier if your starter is quite active) Typically at 24-28°C, a starter fed with a 1:1:1 feeding ratio (equal parts starter, flour, and water) can become active surprisingly quickly, especially once your starter is fully established and in good rhythm. Start watching for bubbles and signs of rise around the 3-hour mark. Most healthy starters fed with an equal parts ratio will hit their peak within 3 to 6 hours at these temperature ranges. Our preference is to use our active starter when it is "young" or on its way up as this provides a more mild taste to bread.
