Yes, I've done this before (I use a fine weave linen cloth as a
filter). It makes a deliciously thick and creamy product and I believe
this is the Greek style way to make it. I try to avoid losing too much
of the nutritional value in the milk so I've been using another method
for thickening yogurt which is to bring it to the boil and then
continue boiling it for ten minutes, let it cool down to the
incubation temperature again then add the culture. That evaporates
about 20% of the water but the whey remains. I imagine that the milk
solids rearrange themselves into a more solid state because they seem
to trap the whey within them.
The accident was caused by starting to heat the milk and suddenly
discovering that somebody had nicked my starter yogurt from the fridge
and eaten it! So I simply brought the milk to simmering temperature
and left it covered for 24hrs whilst I went to bed, went to work and
bought a yogurt to use as a starter on my way home the next day. The
simmered-left-for-24hrs-plus-10-minute-boiled yogurt was brilliant and
worked when I did it deliberately next time. As I said before, this
double boiling method reduced the water content by 33% overall but
since I know the single boiling method already changes the character
of the milk, I can't be sure that reduction in water content is the
only factor involved. That's why I want to try the ten-minute boil on
a reduced-water-content milk for comparison.
I know I don't have to find this out - after all, if a recipe works,
it works. But I'd like to know why.
Nick