How To Warm A Sourdough Starter

Published on
06 October 2020
Gareth Busby
Gareth Busby

Warming a sourdough starter is essential to fermentation activity. Warmth is needed for the yeast and bacteria to ferment the flour. Many bakers in cooler climates struggle to get their starters to rise, and being in the UK, I struggle with sluggish starters in winter, so I have to warm mine up. There isn’t a “best way to warm a starter.” There are several methods to choose that don’t require you to move closer to the equator. Take a look at the suggestions below and see which one will work best in your kitchen.

Why do you need to keep sourdough starter warm?

The Bacteria and yeast in your starter slow their fermentation activity when they are cool. They need warmth to be fully active to make decent sourdough bread. While you can keep a mature starter in the fridge, you’ll need to warm it up every now and again to maintain its activity. A new starter must also be kept warm to boost its activity.

What is the best temperature to keep a sourdough starter?

The ideal temperature for sourdough fermentation is 25-38C (77-100F). You can make a starter at cooler temperatures, but it will take much longer to rise. In my experience, it needs to be above 18C (64F). Otherwise, it won’t mature. Warming a new starter will shorten the time it takes to mature, so it’s in our interest to find a warm place to put it! Also, a new starter that’s kept cold won’t be as populated by the correct enzymes necessary to be used as a levain. It’ll work, but a starter kept at warmer temperatures is much more efficient at creating gas.

How to make your sourdough starter warmer?

So how do you warm a sourdough starter? Well, there are several ways depending on your tools, how warm your kitchen and whether you want to invest in extra equipment. Let’s take a look at the suggestions:

Warm your starter with the oven “proof” setting

Some ovens have a proof setting on them. They are usually set around 30-35C (86-95F), which is perfect for sourdough. However, as you have no control over the temperature, you might find that it works too well, and your starter must be fed more often! The regularity of feedings can be reduced by changing your feeding ratio. See the how to store a sourdough starter guide to learn how to do this.

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Use warm water when refreshing your starter

Using warmer water will warm up the starter. However, this method is only temporary as the starter will cool down in a cold environment. It is a handy trick that can be used for nighttime feeds -to compensate for cooler temperatures in your kitchen. The water should not exceed 40C (104F) to avoid damaging the bacteria. To obtain the ideal water temperature you’ll need to take readings of its temperature with a temperature probe like this one from G Dealer.

Use the oven or microwave light to warm the starter

how to warm a sourdough starter

Placing the starter in the microwave or oven with just the light left on creates sufficient warmth for a starter. In a microwave, you’ll need to be creative in how you keep the door shut. You need to keep the heat in but not completely shut the door, so the light remains on. A piece of cardboard from a cereal box jammed in the door seems to work for me.

If using the oven, you can shut the door and turn the light on. Most ovens have this setting. Just remember to remove the starter from the oven before using it for cooking! This might not be a problem for you, but many home bakers have found other family members have turned the oven on to preheat and baked the starter -which kills it!

These methods are reliable ways to get your starter and your bread fermenting. Unfortunately, the light takes a while to generate enough heat to warm the starter, and if you have no control over what temperature you want to ferment at.

If you don't already have a starter try my sourdough starter recipe.

Put your starter in the airing cupboard

Not every home has an airing cupboard, but those with space around your boiler can use it to warm a starter. It can get a little too hot, though! This method can warm sourdough bread dough as it rises too.

Place the starter on top of the oven

I often put my dough on top of the oven for its final rise. It warms it up just enough to speed up the rise. You can do the same with your starter, but it will only be a temporary fix while the oven is in use.

Warm the starter on the window sill

Have the sun warm it up. It works surprisingly well. Some bakers find that the sunlight damages the starter, so avoid transparent containers just to be sure.

Use a home proofer to warm the starter

Brod and Taylor home proofer

Although it’s an additional cost, a home proofer offers the most consistent temperature and humidity levels with the most minor worry. Pop your starter in, set the temperature, and off you go. No need to panic! The Brod and Taylor home proofer (pictured above) can also be used to precisely bulk ferment and proof your dough, so despite the outlay, many home bakers that get one find they can’t live without it! View the latest price at Brod & Taylor or see Amazon

Use a yoghurt maker to store your starter

It might sound silly, but I found a secondhand yoghurt maker for around $15 (£12), and it’s awesome! Just like the home proofer, I can set the temperature accurately to make the perfect sourdough starter warming box! My happy starter loves it! But there isn’t enough space to fit dough inside it.

Make a DIY proofer for your starter

It can be tempting to build your own proofing box to save pennies! I tried it, and found that it works really well! The insulating mats I used were pretty cheap, and running costs are very low. A thermostat can be used to achieve accuracy, just like the Brod & Taylor. You can make a large proofing box for several loaves or small enough for just a starter jar. Here’s how to make a DIY proofing box.

Your starters temperature affects the flavour of your sourdough bread

The temperature of the starter impacts its flavour by cultivating more lactic or acetic acids. Therefore, being able to adjust the temperature accurately and making it constantly the same will change how the starter (and therefore the bread that’s made) tastes and smells. To achieve this, you’ll need to be able to control the temperature with a thermostat. However, some bakers like the daily changes in the flavour of their bread. It’s kinda the fun of sourdough, isn’t it?

Further reading: How to make sourdough more sour


There are many solutions to the problem, which depend on how much warming you have to do and what you already have around you. Buying a proofing box is the most reliable way. Though you can use the other techniques for a decent enough heat boost. If you’re just starting out in your sourdough journey, check out my sourdough bread recipe for beginners. It breaks everything down into simple steps and should help you make fantastic bread.

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