Keeping your sourdough starter warm, especially during winter, is vital for good sourdough starter growth when making your own sourdough bread. The colder it is, the closer to hibernation your sourdough cultures will become. Think of it like this – when you are cold, what do you want to do? Curl up in a ball and hibernate. Sourdough starter does the same thing.

That’s where this cool kitchen hack comes in handy!

When you are feeding your culture only, and not preparing it to make bread at that moment, keeping it warm is not essential. In fact, keeping it fairly cool is more effective. Temperature affects the speed at which sourdough starter grows.

Just like you feel more active in warm weather and want to huddle at home in winter, your sourdough likes to do the same.

Warm = faster growth
Cool = slower growth
Cold = hibernating

In the same way, if the temperature of your water or the environment for your sourdough is too cold or hot for you, it will be too cold or hot for your sourdough.

Warm temperatures accelerate the growth of sourdough cultures and all that growing makes it hungry. In a very warm environment, such as the peak of summer, sourdough starter needs to be fed up to 3 times a day!

When you want to make bread, a highly active sourdough starter will produce the best results.

If you are maintaining an active sourdough starter, a slower growth rate means you need to feed it less often. So a handy hint – keep it somewhere inside air-conditioning or a cool pantry during summer for a slower growth rate, or the fridge if baking once a week or less. If you want to read about doing this long-term read about this easy process here. If you don’t want to maintain a starter at all but keep it in your pantry across all seasons, try our Pantry Sourdough Starter. Feed it only when you need it.

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Easy game changer

The structure of your sourdough starter determines the structure of your finished loaf of sourdough bread.

If your sourdough starter is puffy and light, your sourdough bread will be puffy and light, given the two dough rises go well.

If your sourdough starter is flat and dense, your sourdough bread will be flat and dense too.

Partnering with the quality and protein content of the flour you’re using, temperature and timing will be the biggest determining factors in a strong sourdough starter.

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So how can you keep sourdough starter warm, even in the winter months?

If you are using our Pantry Sourdough Starter, you will know it’s too cold for your starter when it did not grow after Feed 2 and there are no signs of life – bubbles on the surface or through the sides of the jar. The mix is thick and stagnant.

If you are using your own sourdough starter, and it isn’t growing due to the temperature, it’s likely to look the same – no growth with no bubbles.

Never fear, there are many ways to keep sourdough starter warm, easily! But before I dive into this, I must share with you something that’s SO important; it’s a game-changer. If you don’t know the following, keeping your sourdough warm will only make the issue of it not growing – worse.

Don’t be deceived!

When sourdough starter is highly active but has become exhausted, it looks almost exactly the same as a sourdough starter that is struggling to grow. Only this starter is super active and the last thing it needs is to be left longer at warmer temperatures. What this sourdough starter needs is shorter rest time and more regular feeds. Or, a faster turn around into making dough.

What looks the SAME between a sourdough starter that isn’t growing and won’t that has become exhausted?

In both instances; the amount of starter in your jar will be the same as when you last fed it. The one that isn’t growing didn’t expand. The one that did… grew so much it shrunk back again.

Use an elastic band around your jar or a white board marker and mark the level of the starter in the jar when you feed it. This will show very clearly any growth, or not, of the starter. Believe it or not, a sourdough starter that has grown and become exhausted will, over time, shrink back to exactly the same level it started at. Hence, just like a sroudough starter struggling to grow, the mix does not look like it has grown, when it has; a lot.

What’s different?

Sourdough starter that has not grown will have a thick consistency. The flour in the starter has not been digested or fermented by the sourdough cultures and the mix is in fact ‘just sitting there’.

Sourdough starter that has grown but has become exhausted is runny. The flour in your starter has been digested and because the cultures are highly active, there are loads of tiny air bubbles on the surface of the starter. The more you move the jar, the more the air bubbles will disintegrate. And the consistency will become more dense, less airy but remain wet.

What happened?

When a sourdough starter gets exhausted, the starter did grow but you didn’t feed it or turn it into dough when it doubled. The starter grew hungry and eventually, did not have the energy to keep holding the puffy airy structure. Your sourdough starter passed peak performance, grew weary from lack of food and deflated like a balloon.

You may not have seen this happen.

This can happen if you are busy and the day or environment is warm, you forgot to do the next step, left it too long or it may have also happened through the night. Whatever it was, I can often miss it too. If I had seen it, it wouldn’t have happened.

Sourdough starters get exhausted because the sourdough was left to rise longer than it needed. Warm temperatures are often the cause. An exhausted sourdough starter will result in an exhausted (dense) loaf of bread. Feed it again, even if you have to discard 2/3 to do so, before you make a loaf of bread. When it doubles, move on to making dough.

Warm temperatures benefit sourdough starter greatly, however, when temperatures go up, time-frames come down. Things can start to move very quickly.

Why keep sourdough starter warm when it’s cold?

When your sourdough starter is having trouble growing, it’s often a temperature issue and there are plenty of ways to help it along, using things that you may already have at home.

If you are using our Sourdough Starter and recipe, you can also use these ideas to speed up the entire process because warmer temperatures means shorter growing times. But you will need to be attentive to your sourdough so that it gets the next step the moment it needs it. Hint – any time the sourdough doubles, it’s ready for the next step.

Flow with your sourdough

No matter how you are making your sourdough it’s important to flow with your starter.

So let’s move on to finding some micro-environments around your home that your sourdough starter will love. So even when your kitchen is cold, your sourdough won’t be!

If the top of your sourdough starter turns yellow…

Sometimes when you’re artificially keeping your sourdough starter warm, the surface turns yellow and becomes dry. This is usually caused from providing direct heat underneath the jar – EG From using a heated base such a seed mat or your internet router. These are excellent ways of keeping you starter warm and I use both all the time. However, they are not ambient sources of heat that warm the environment, just the jar, from the base up.

If your sourdough starter turns a little yellow in your efforts to keep it warm this way, it’s not a problem. Underneath the dry, crusty surface will be fresh bubbly sourdough starter, Simply dissolve the dry surface in the next feed or addition of water. If it’s really bad you can just remove it.

15 Easy ideas for keeping your sourdough starter warm even in winter!

Now, remember, you want to keep your sourdough starter warm – not kill it! In temperatures over 50°C (120°F) sourdough cultures can die from overheating. If your little ‘warm spot’ is feeling too hot for your own comfort, it will also be too warm for your sourdough.

Ambient warmth is better than direct heat. Direct heat, such as a seed mat or sitting directly on top of your internet router, can dry out the surface of your sourdough. Try wrapping the jar in a thick towel as insulation between the sourdough and the heat source, and trapping the radiant heat inside the towel, creating ambient warmth around the jar.

1. The hidden gem in your house
Most of us have somewhere in our house that’s consistently warm, usually an appliance that’s on all the time. E.G on top of the fridge, near our internet router, the PS3, a coffee machine etc. If you place your sourdough mix near the item, the radiant heat will keep the sourdough starter nice and warm throughout the growing process. I use this method the most. Be warned – the sourdough starter can grow very quickly!! And become exhausted if you don’t catch it in time and move to the next step in the process.

2. Try your oven with the light on
Another hack for keeping sourdough starter warm would be to use your oven with just the oven light on. This will give an even temperature somewhere in the moderate to warm zone. Some ovens reach temperatures of 50°C (122°F). This temperature will kill sourdough. You may need to leave the love door ajar or try the next idea and use your dutch oven as well.

If you have a thermometer that measures air temperature, measure the exact temperature of the oven with the light on so you know what you’re working with. If you don’t have one, the first time you try it check your sourdough regularly. If your sourdough shows lots of activity (bubbling and rising) within several hours of your last feed your little spot is perfect!

3. Use your dutch oven with your oven with the light on
If you’re finding that your oven is too warm for your sourdough starter, even with just the light on, place your starter inside your dutch oven or another baking dish with a lid. This will insulate it from the heat while still keeping your sourdough starter warm and cosy.

4. Chase the sun
Placing your sourdough near a sunny window will increase the temperature and help keep it warm. Glass is like a magnifier so using a window plus a glass jar can be lethal if the day is warm but it can also be your saviour. Just lift the lid and check the temperature inside your jar if you’re not sure. You will know if it’s too hot or not; your sourdough likes the same moderate (comfortable) temperatures that you do.

Remember! The aim is to be as close to moderate as possible or warm (if you want a really fast process), you don’t want the area too hot. Don’t exceed 50°C (120°F) it will kill your sourdough. 😢

5. Use warm water
Warm water doesn’t stay warm for very long but it’s like your morning coffee – it gives the sourdough a little boost. Use it when feeding your sourdough and even making your dough if you’re wanting to speed up the rise or, your kitchen is very cool. You can combine this option with another idea for keeping your sourdough starter warm and cosy, especially if #6 below is your only option. The combination of warm water and the additional few degrees warmer will increase the opportunity of your sourdough growing nicely.

6. Heat rises
If you don’t have a ‘warm spot’, heat rises. Try placing your sourdough on the top shelf or on top of a cupboard to stay warm. It’s can be 1-2 degrees (Celcius) warmer than just sitting on your bench-top.

7. Try your microwave
Do NOT put your microwave on!!!! Even in its idle state, your microwave is an insulated box and may protect your sourdough environment from both extreme cold and hot temperatures. To keep your sourdough starter warm at a consistent temperature, this may just be the cheapest and quickest fix? 🤔

8. Try your microwave again
Place your starter in the microwave to warm up. Leave the door just barely shut so the light stays on. The small space with the light on can warm the area enough to help the starter grow. it can get upwards of 32°C (90°F) which is getting quite warm. Consider shutting the microwave door at this point, it will hold in the heat (very slowly releasing it) while turning off the light so that it doesn’t get too hot. You can always ajar the door again to switch the light back on if you need to.

Some microwaves are smart enough to save electricity by turning the light off when the door is left open for a certain amount of time. If this is your microwave, place two mugs of boiling water inside and shut the door. Replace the water in a few hours if necessary, It’s an insulated box so it will take a long while to drop the temperature.

9. Use a blanket
Try placing a blanket or heavy towel over the jar to insulate your sourdough starter from cool air temperatures. Surprisingly, this can be a simple way to help keep your sourdough starter warm, especially if it’s in a lukewarm spot that could do with a little extra help!

10. Try your car
If it’s really cool where you are, try placing your sourdough starter in a warm car. Be mindful that temps can get hot in there! But it can be a magnificent environment for keeping your sourdough starter warm when parked in the shade on a cool day or in the sun on a cold day. Don’t exceed 50°C (120°F) inside your car or jar!! It will kill your sourdough. 😢

11. Do you have a large thermos?
Pre-heat a large thermos with warm water. Place your jar of sourdough starter inside to keep it warm and seal with the thermos lid. Leave for several hours and check for growth. If you need to, heat the thermos with warm water again and leave until the starter doubles, or the next feed is due. Don’t leave a sourdough starter for longer than 24 hours without feeding, even if there has been no growth.

12. Buy a seed mat
Use a seed mat WITH a thermostat so that you can control the temperature. This is an easy way to keep sourdough starter at a constant temperature with low heat which will warm, not won’t kill the culture. Just remember to hack this one to help create ambient, rather than direct heat from the bottom in a cold room. Wrap the jar inside a towel to insulate and trap warmth around the jar. Seed mats are also good for keeping kombucha and water kefir warm for developing magnificent fizz! Just be careful… if left too long without ‘burping’ both water kefir and kombucha can become so effervescent that they can burst from pressure build-up inside the bottle.

13. Under a lamp
You could place your sourdough under a lamp that’s switched on (non-LED as they don’t generate heat). You could also place the lamp and the sourdough in a cupboard to trap the heat being created by the light bulb. A cardboard box works well also, but bear in mind heat and cardboard can be flammable. Don’t let the lightbulb touch the cardboard directly. This is best supervised – meaning, don’t leave this one home alone. 😊

14. Use your electric blanket
This one is funny but cute. My mother-in-love is the inspiration behind it. When she was here, we used to holiday together every year and I can’t cook rice without a rice cooker. So this was her domain. She used to boil the rice and pop the saucepan in her bed to finish cooking. Oh I love her still! So if you have an electric blanket on your bed, pop it on low and slide your little sourdough jar or bowl under the covers. This won’t work overnight while you are sleeping but it will work during the day and give your sourdough a good dose of cosy! 😊

15. Invest in a proofing box
I wasn’t sure whether or not to include a proofing box as an option for keeping sourdough starter warm because most people won’t have one and it’s a fair investment. Therefore unlike all the options above, it doesn’t support my goal to make sourdough so easy that anyone, anywhere can make it. But since you can achieve the same results with any of the above, I decided to include it because it’s just so damn cool! It’s multi-purpose too if you like to cook AND it folds away. It looks like a great tool for us foodies! I don’t own one (yet) so I can’t tell you if it’s worth it or not but if you invest in one, I would love to hear about it. When I do get one, I will re-write these last few sentences and let you know what I think.