It has been cold and snowy where we live and I have had to so some extra baby -sitting with my sourdough starter. I want to make sure I have enough starter for waffles tomorrow morning and enough for six loaves of bread which means I need that sourdough starter to get working on that ground kamut and now. This means it is sitting cozy next to the Crock-Pot with bone broth for tomorrow's soup. If you are seeing your ferments slow down in the cool weather, keep reading.
Ferments prefer warmer weather which means that very warm weather can sometimes be too much of a good thing and yield too quick of a turn around. But the opposite it true, too. This means that when the mercury drops, so does the production of our ferments. When your kitchen and your house are cooler, you have to take some extra steps. They aren't hard, just a regular part of food pet maintenance.
Provide them with a heat source. If you have a Crock-Pot hard at work making you some delicious bone broth, snuggle up a ferment right next to it. If I am making sour cream or viili or other room temperature dairy cultures, I can speed them up bu making sure they sit in their containers around the pot. Only keep them together if they are the same culture, though. If you have a microwave, you can heat a rice sock and place it around or under (remember that heat rises) your container to help give it a boost of warmth. This is particularly helpful if you are giving a bit of a boost to a slow to react sourdough starter or a sourdough loaf that is rising too slowly. Sometimes I heat a bath towel in the dryer and wrap it around my container to give it some warmth. If you are doing a counter-top proof of sourdough bread, this can be very helpful in the cold months.
Move them away from drafts and cover them if necessary. This means away from windows which can be a cold sink as well as away from doors to the outside which open frequently. You might find that you are keeping them outside the kitchen since they both need some protection from the cold as well as from each other in order to prevent cross contamination. I have been known to keep them in my dining room on the buffet against the wall. If you keep your house very cool at night, you might want to cover them with a warm towel while you sleep to make sure that they maintain their warmth.
When I am fermenting vegetables and fruits using my whey starter, I keep them on a tray with the culturing dairy. This way I can move them easily and cover them with a single towel to make sure that they all stay warm. It does mean that I make sure to be consistent with which starter I am using.
Don't forget anything undergoing a secondary ferment, it needs warmth, too. If you are doing a secondary ferment with your kombucha or your water kefir, you might find you get more effervescence if you make sure that bottles are in warm spot. You can simply cover them or move them elsewhere. If very tightly sealed in well washed bottles (I mean the outsides), I do not worry putting them with other ferments.
Keep them in an enclosed space. You can put your ferments in the microwave (which you aren't using anyway, right?), in a cooler with the lid on, a closed cupboard or even in the oven. When I put things in the cupboard, I hang something on the handle to remind me that I need to check the ferment inside. When I put things in the oven, I always leave the light on so that I can see into the oven and won't turn it on with my ferments inside. If you do not have a window in your oven, place a magnet on the front or tie something to the handle as a visual reminder. It is critical to make sure the other members of your family know what you are doing. I have heard of whole crocks of dead sourdough and cracked jars and I really don't want that to happen to you.
Develop some patience. This December we had a large party and my son started some cinnamon beets well in advance to make sure that they would be ready in time. It did take longer than we wanted and this was even with a daily warm towel wrapped around the jars. Being a traditional cook means being subject to the natural elements in some ways and this is a prime example. Your sour cream might not be as thick or as tangy or ready when you want. Sorry. This is life. Try to keep this in mind when you are hot and panting this summer and your dairy kefir is just making cheese. It is all a cycle and we should just be grateful for each stage in the cycle, it won't last and soon we will be plagued by the opposite.