A Cheaper Sourdough Starter Incubator

tldr: I built a sourdough starter warmer for much less than $170. It’s not beautiful, but it’s fine, and cost about $40.

The cold shop and the expensive alternatives

During cold months in Seattle, in an incredibly inefficient pizza shop, it’s nearly impossible to keep a sourdough starter at a proper temperature. Ideally, this is around 70-75°. (I’m only occasionally baking sourdough, so I'm not too keen on the goldilocks zone of 75-82° which accelerates things past my schedule.)

But the pizza shop is normally around 60° until the ovens turn on. (The ceilings are double-height, the industrial heater is loud and really only heats the loft.)

Sourhouse and King Arther and Brod & Taylor all have sourdough starter “homes” for a ludicrous price of $99 to $169. (They look good, though!) I can’t imagine they're anything more than an insulated home for a coffee warming puck. So let’s just try and recreate them I said to myself. Except for the insulated part, so this is more of a version 0.5.

The idea

Try out the cheapest coffee-warming puck on the market, pair it with a temperature controller, and put it in a container to house it all. I expected to return each component and replace it with something slightly better until I found a working combination, but the first couple of items have been working pretty well for around 6 weeks! It’s not beautiful, but it’s fine, and I’ve found a few changes to implement for version 1.0. (Hint: it’s just insulation and aesthetics.)

The coffee mug warmer

The one I bought has already gone up a few bucks, but I still $15 to be worth it. It also doesn’t turn off automatically, which you definitely don’t want—I had assumed it might. It uses 10 watts when it’s on, and is powered by USB, so any old wall charger from an old phone will work.

Mug Warmer

The temperature controller

It’s super simple: set a high limit and a low limit. When the thermostat hits the low limit, it turns on the warmer; when the high limit is finally hit, it switches off.

I bought mine for $20.99, and it’s down to $18.99 right now. The app isn’t super terrible, but it would lose the connection frequently in those first days of monitoring until I force quit, reopened, and tried again.


I use similar (but more reliable) controllers for the two freezers I set up as refrigerators for all the cheese I go through, and they’ve been humming along perfectly for a couple years now. Deep freezers have a lower profile for a fraction of the cost of a regular fridge.

Adding a bit of energy storage to smooth things out

The temperature controller and mug warmer worked well enough, but I realized most of the heat was quickly escaping, and a little heat storage would be useful. The warmer was on more than it was off.

So, I filled a small mason jar with water and set it on the puck as the puck is intended to be used! The heat stays around long(ish) after the controller turns off the warmer.

Temperature fluctations

Is it safe?

Is this safe? I think so! But I don’t know so. The mug warmer does have that air of cheapness surrounding it, so I’ve kept a close eye on things for this six weeks of testing.

All put together

Initially I put the lid back on this food storage container, and it was fine. Wires kept it from closing completely, so replacing it with the “blanket” made it a bit better.

Outside the sourdough incubator Inside the sourdough incubator

Future changes

First, an insulated container! Then, get the wire stuff out of the way a bit more. Put it in a cupboard for another bit of separation from sunlight warming or temperature fluctations and I’m (you’re!?) all set.