What happens if you overheat cream when making crème fraîche?
I have made yogurt and crème fraîche a few times with at least decent success Recently I tried zapping about a cup and a half of cream for a minute to give it a head start before adding the crème fraîche culture, and it seemed rather warm. After 36 hours it was still very thin, even with a few hours in a warm water bath. Then I added a bit more crème fraîche in case the heat killed some of the culture. After about 51 h (last 14 h or so in a warm water bath, though with time that cooled), it thickened but doesn’t taste great. I put it in the fridge, where it got really thick (but then thinned out with stirring). It’s a bit hard to describe, but one word I would not use is delicious, the way good crème fraîche usually is. I also noticed a thin layer of clear liquid on the bottom. Could you help me understand what happened and why? Could you point me to a good book or other resource to learn more about culturing processes?
District of Columbia County District of Columbia food preparation
When you say you "zapped" the cream, I take that to mean that you heated it in the microwave. Then you say, "and it seemed rather warm." In doing this you may have heated some or all of the cream too hot. Heating in the microwave does not produce an even heat so there may have been hot spots in the cream. That extra heat can have a number of effects that could adversely affect the outcome of your process:
1. The proteins in the cream may have been denatured. This may have decreased their ability to set together rather than separate into curds and whey.
2. Some of the bacteria and enzymes that are needed for positive fermentation may have been destroyed at the higher temperature.
In general, overheating can produce off-flavors.
The National Center for Home Food Preservation at University of Georgia Cooperative Extension has a good fact sheet for making yogurt at home at http://nchfp.uga.edu/publications/nchfp/factsheets/yogurt.html. It also describes some trouble-shooting options.
These resources all refer to yogurt, not crème fraiche, but the processes are very similar.
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