A: You can use a heating pad placed around it, flip it on the lowest setting for a few hours a day. You can also place a towel or blanket (wool if you have it) around the jar to insulate it. If you don't have a heating pad, setting up your brewing space next to a heating vent or high on a shelf in a warm room usually does the trick .
We are located in Madison, WI so we're definitely privy to brewing in cold temps! Here are some of our top tips for brewing in the winter time:
1) In the winter, we prefer to move our jars up to a high shelf in a warm room. Like on top of cupboards or a tall bookshelf. Sometimes this means setting up the brew jar upstairs where it can be warmer if you have a multi story home.
2) If you brew jar is resting on a cold countertop, place a book or cutting board underneath it for insulation
3) If taking those steps doesn't get the temperature above 68, we do recommend using a heating pad, setting it on its lowest setting, and wrapping it around the jar. This can be very effective in maintaining a consistent temperature in the mid 70's.
The trick with using a heating pad it checking in on it so that it doesn't get too warm. Our brewing kits come with a temperature gauge so it will be easy to always read the temperature on the side of the jar. If your heating pad keeps the brew too warm (in the mid to upper 80's is too warm) then just flip it on for only a few hours a day.
You can keep a towel wrapped around the heating pad and jar so once you flip off the heating pad it will help to retain some of that heat for a few hours after.
As for the second fermentation - it is less necessary to keep the temperature in the 70's. Simply store your kombucha bottles somewhere they will stay above 68 degrees. If you want to move the second ferment along quicker, then store them somewhere warmer.