Warming to kick-start activity in your sourdough starter is a great way to get things going. A sourdough starter needs warmth to allow the yeast to ferment the starches in the flour. If you don't already have a sourdough starter, you can use my how to make a sourdough starter guide.
The ideal temperature for sourdough fermentation is 25-35C (77-95F) whilst a temperature above 20C (68F) shouldn’t cause too much of a problem, it’ll be slow to rise.
Here are a few ways to warm a starter that don’t require you to move closer to the equator. You can also use these tricks to warm your proofing bread too.
The oven proof setting
Some ovens have a bread proof setting on them, they are usually set around 30-35C (86-95F) which is perfect. Using this method will mean you will have to feed twice a day. It might be to warm for bread made with a long bulk fermentation so keep an eye on the dough so it doesn't over ferment.
Oven or microwave light
Placing the starter on a tray in the microwave or oven with the light on is enough warmth to keep the starter active. You might have to be a bit creative to keep the door close on the microwave without the light turning off, otherwise this is quite a solid way to allow your starter and your bread to ferment.
Place on top of the oven
I often put my dough to final rise on top of the oven. It warms it up just enough to speed up the rise. You can do the same with your starter but it’s only going to be a temporary fix whilst the oven is in use.
On the window sill
Have the sun shine in on your starter to warm it up. It works surprisingly well so I use this trick quite a lot.
Warm the water
Using warmer water will help kick start activity. Though it won’t last forever, in cooler environments it can give your starter or bread a nudge in the right direction.
Use a proofer
Although costly and hard to get hold of a proofer offers the most consistent temperature and humidity levels with the least amount of worry. Pop your starter in, set the temperature and off you go. No need to panic!
Here’s the only one I can find that doesn't cost thousands. At the moment it’s not available in every country so you’re lucky if you can get one. Fantastic reviews too!
It can be tempting to build your own proofing box. Personally my research has found that unless you are in desperate need of a custom sized proofer, it’ll end up more expensive to make one than it would be to buy one.
Here's a video explaining how to do it nonetheless:
The airing cupboard
Not every home has an airing cupboard but those that do have space around your boiler can find that your starter will be nice and warm in there.
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 to get an occasional 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 to make fantastic bread.