TIPS: How to keep your sourdough starter warm
11/3/2014: A recent TFL forum post inspired me to think about ways to keep your starter warm.
Maintaining a warm temperature is extremely important to establishing a new starter. If you maintain your initial starter temperature at 82-86F, this will lead to the production of more lactobacillus than yeast, meaning a more sour/acid environment, which is important to establishing a healthy yeast and bacteria colony in your starter, especially at the beginning.
Once established, maintain your starter between 72-80F; this will help improve the speed of yeast growth. Want more lactobacillus, or more yeast activity? Take a look at this handy chart of yeast and lactobacillus growth, and choose the starter temperature that will work best for what you're trying to achieve.
I live in a part of Southern California where the weather is 75F on average about 300 days out of the year, so home warmth is generally not a problem. But what if you live where it's cold in the winter? Here are 9 ideas for how to keep your starter warm when it's cold:
1. Sunny spot by a window. Easy and cheap, with one caveat: place your starter in a shoebox or other opaque or dark-colored box. Yeast and direct sunlight don't mix well. Of course dark colors will also help keep the box nice and warm in the sun too.
2. Added 12/14/2019 - Double-insulated thermos: you could add some warm water to a double-wall vacuum-insulated thermos, then add starter in a double-bagged ziploc bag, seal the whole thing up. The larger the thermos and the more water as thermal mass, the longer it will keep your starter warm. You could probably maintain the temp heating up some metal or ceramic rods (or maybe even some sand!), placing them into a double-insulated container, and setting the starter on top. I have used this method multiple times and it works fantastically well! The trick is to not to add in too much warm water, because the bag will expand and the hydraulic pressure could cause damage to the thermos.
4. Cardboard or plastic box with a lamp. Run a low-wattage incandescent lamp/light bulb into a sealed box, turn the lamp on, and position your starter somewhat away from the lamp. A cardboard box or ubiquitous 20gallon plastic bin could be useful for this.
5. Use your oven light. Simple as that: keep your starter in your oven with only the oven light turned on. It's easy to adjust the temperature by how close you place your starter container to the light.
6. Next to your home heating system. Put it next to your home heating vent, wood stove, home furnace, water heater, fireplace, etc.
7. Old miner style/next to your body: put your starter in a small double-bagged ziploc bag, and keep it close to your body, in a shirt or jacket pocket. Just like the "old sourdoughs" used to do when prospecting. This option is the most affectionate method, and results in the most bonding with your starter ;)
8. Brod & Taylor Proofer. A lovely and functional option, if somewhat expensive. The Lexus of home proofing and warming options.
Any other ideas I missed? I'd love to hear 'em.