Keep your Sourdough Starter Warm: 10 Easy Tips!

Temperature is probably the most important factor that decides how quickly (or slowly) your sourdough starter peaks and is ready to bake with. If your starter is sluggish, read on for some easy things you can do to keep your starter nice and warm!

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Most starters will adapt to whatever your room temperature happens to be. Before trying anything to keep your sourdough starter warm, leave it at room temperature for at least a week. Make sure you’re feeding it enough and following these instructions for how to feed and maintain your starter. If your starter is still slow to peak and your home is on the cool side, try some of the ideas below.

But before diving into all the ways you can keep your sourdough starter warm, grab a probe thermometer so you can check on your starter regularly. You want to make sure it isn’t getting too warm—if it gets much higher than 82˚F or 28˚C you risk weakening or killing your starter. This is my favourite thermometer to use because it’s very durable and easy to use.

Here are a bunch ideas to keep your sourdough starter warm, starting from the easiest and least expensive:

Put it on top of the fridge

Refrigerators get cool on the inside by removing heat and transferring it to the sides and top of the fridge. This means the top of your fridge could be a great place to keep your starter warm! The first few times you do this, use a probe thermometer to check on the starter regularly, to make sure it isn’t getting too warm. If it’s getting any higher than about 85˚F (29˚C), try one of the other ideas in this post instead.

Keep it warm on a windowsill

Find a warm and sunny windowsill to put your jar. Remember to place it in a paper bag or wrap it in a tea towel first though. You want to avoid exposing the starter to direct sunlight. You may want to use a thermometer to check on its temperature from time to time to make sure it isn’t getting too warm! If it is, try one of the other methods on this list for keeping your starter warm.

Place it in a bowl of warm water

Put your jar of starter in a large bowl. Heat some water to around 90˚F (29˚C). Gently pour it into the bowl around the jar until it reaches the level of the starter—any higher, and the jar might tip over.

Put it in your slow cooker or Instant Pot

Boil some water in a kettle and pour it into a mug. Place the mug in your slow cooker or Instant Pot along with your jar of starter, and cover the slow cooker with its lid. Don’t turn it on though—even on low it will be too hot for your starter.

Put it in the oven with the light turned on

Even at its lowest temperature, an oven is too hot for a sourdough starter when turned on. Even the proofing setting on most ovens is too hot. But if you simply turn the light on and close the oven door, the temperature could be just right to keep your starter happy. The first few times you try this put an oven thermometer in with the starter just in case, because some oven light bulbs run hotter than others. Check on it regularly to make sure its temperature doesn’t get any higher than about 85˚F (29˚C). And definitely put a clear sign on the oven to warn everyone not to turn it on. Lots of bakers have had their sourdough starters ruined by accident this way, so please be careful! I always recommend making a backup of your starter just in case.

Put it on top of a heating pad

Anything that warms within the range of 75-82˚F (24-28˚C) is perfect. Seed starting and fermentation mats work well, and this sourdough warmer can even be set to a specific temperature. If your mat or warmer can’t be set to a specific temperature, try a low setting first and check the temperature of the mat after 30 minutes or so and adjust from there. Once you dial in what setting gets you a temperature within the right range, set it to that and place your jar of starter on it.

Make a DIY proofing box

It’s actually really easy to do! All you need is a styrofoam cooler, a seed starting or fermentation mat, and a temperature controller. These are fairly inexpensive to make compared to the cost of buying a dough proofing box, which can easily cost hundreds of dollars. If you make one it will also be useful for bulk fermentation, proofing sourdough and store-bought yeast doughs, and other fermentation projects such as making yogurt—so I think it’s well worth the investment! Here is a video showing you how it’s done.

Sous vide your starter

It would be a bit excessive to buy a sous vide machine just for keeping your starter warm. But if you happen to have one anyway, why not give it a try? Sous vide machines are designed to keep water circulating at a precise temperature even for long periods, so it can be the perfect tool for keeping your starter at a good temperature. Place your starter in a large pot or plastic tote, and fill it with water until it meets the level of your starter or at least the minimum level for your sous vide. Then set your sous vide machine to somewhere between 75-82˚F (24-28˚C). Make sure your starter jar is covered but not airtight, and that it’s not at risk of tipping over into the water. The last thing you want is to have your starter leak out into the sous vide water and potentially ruin your machine, so proceed with caution.

Use a store-bought proofing box

A great choice would be this popular and highly-rated one from Brod & Taylor, which folds up for easy storage. It’ll also come in handy for proofing any yeasted doughs (including sourdough) as well as fermentation projects so it could be worth the investment for you. Again, you’ll want to set it to somewhere between 75-82˚F (24-28˚C).

Use a specialty sourdough starter warmer

The Goldie from Sourhouse, the Sourdough Home from Brod & Taylor, or this inexpensive sourdough warmer are all great options. The Goldie and Sourdough Home can also keep your starter cooler than room temperature. This can be useful if your home gets really warm in the summer and you want to slow your starter down, but not as much as you would by putting it in the fridge. The Sourdough Home cools itself electronically to a preset temperature, while you can get a cooling puck for the Goldie.