Electric Heat Fermentation Box — USB + Foldable

The Perfect Environment Every Time

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 on the market are bulky, expensive, and packed with dials you don't need. Ours is the opposite: $34.95, one optimal temperature, no fuss. We've dialled in the perfect warmth for sourdough — a steady 28°C, so there's nothing to set or adjust. Plug it in, place your bowl inside, and let the foil-lined interior do the rest.

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 (5V) — 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 box maintains a gentle temperature of around 28°C (with slight variations depending on the volume being warmed inside) — the ideal environment for encouraging strong, active starter growth. There are no settings to adjust or temperatures to monitor; simply place your starter/dough inside and let the box do the work.

Whether it's the height of summer or a frosty winter night, the box helps maintain a consistent temperature so your starter stays comfortable and active, without the overnight cold shocks that can slow fermentation.

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 approximately 28°C. The time taken 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.

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 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 this temperature. 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.