days. The thick version is fermented with the
typical cream culture for 15 to 20 hours, and
has a shelf life of 30 days. As with all
fermented milks, the thickening is an
indication that the product has reached a
certain acidity (0.8%, pH 4.6) and so a distinct
tartness. Commercial American crème fraîche
is made essentially as the French fermented
version is, though some manufacturers add a
small amount of rennet for a thicker
consistency. A distinctly buttery flavor is
found in products made with Jersey and
Guernsey milks (rich in citrate) and with
diacetyl-producing strains of bacteria.
Making Crème Fraîche in the Kitchen A
home version of crème fraîche can be made
by adding some cultured buttermilk or sour
cream, which contain cream-culture bacteria,
to heavy cream (1 tablespoon per cup/15 ml
per 250 ml), and letting it stand at a cool room
temperature for 12 to 18 hours or until thick.