Greek homemade yogurt

Yes — what she was doing is a very traditional and completely legitimate way of making yogurt. In fact, the details you remember are quite consistent with how generations of Greek and Balkan households made yogurt without a yogurt maker.

The interesting part is that the long 24–36 hour room-temperature incubation can work, provided the conditions are right.

What was happening

1. She boiled the whole milk

   • This wasn’t merely for sanitation.

   • Heating milk to around 180–190°F (82–88°C) changes some of the milk proteins, particularly whey proteins.

   • That helps produce the thick, set texture characteristic of homemade yogurt.

   • She probably held it near the boil for a little while rather than merely bringing it instantly to a boil.

2. She let it cool naturally

   • The traditional “finger test” is surprisingly effective.

   • She was looking for roughly 105–115°F (40–46°C) — warm but not painfully hot.

   • If the milk is too hot, it can kill the yogurt bacteria.

3. She added yogurt from the previous batch

   • That’s the classic back-slopping method.

   • A small amount of the previous yogurt contains Lactobacillus and Streptococcus thermophilus cultures.

   • Once you have a good batch, you can keep using it as the starter for subsequent batches.

4. She wrapped/covered the pot and left it alone

   • Even without an appliance, the milk itself retains heat for quite a while.

   • The bacteria gradually convert lactose → lactic acid.

   • As acidity increases, the milk proteins coagulate and the milk becomes yogurt.

But 24–36 hours is unusually long

That’s the part I’d be especially interested in.

A conventional yogurt culture at ~110°F might set in 4–8 hours. At ordinary room temperature, fermentation is much slower, so 24 hours or more isn’t crazy.

And there’s a traditional advantage: long fermentation produces a much more acidic yogurt.

If she was leaving it for 24–36 hours, she may have been making something considerably more tart than modern commercial yogurt.

The other possibility is that the actual temperature of the room and container mattered enormously. A heavy stainless-steel or enamel pot, covered with towels or placed somewhere warm, can maintain a surprisingly favorable temperature for several hours even though there is no active heating.

The really beautiful part

The system is essentially self-perpetuating:

milk → yogurt → starter → yogurt → starter → yogurt

She didn’t need a packet of culture, thermometer, yogurt maker, or even a recipe. Her “finger thermometer” and experience were the technology.

And there is a fascinating possibility with her particular yogurt: the culture may have adapted to her household’s repeated batches over many years. The microbial community in homemade yogurt can change somewhat depending on the milk, temperature, incubation time, and repeated reuse of starter.

If you want to recreate her exact old-fashioned Greek method,  I can give you a gallon-of-whole-milk procedure that deliberately uses the finger test and 24–36 hour room-temperature fermentation, rather than the modern 6-hour yogurt-maker method.