Slightly Warming the heavy cream in the microwave for about 25 seconds makes the process faster. It takes me approx. 20 hours when I warm the mixture and when i don't it takes about 26 hours.
Total time depends on the room temperature. warmer the room, lesser the time.
This recipe can be easily doubled.
The acid during the fermentation process keeps the harmful bacteria away, so don't worry about placing this on the counter.
The taste differs slightly, depending on the heavy cream or the culture (Yogurt or buttermilk).
Best if used within 7-10 days.