Tell-Tale signs of fermentation
During fermentation, milk is used up to be replaced by white solid curd, floating in watery whey. If the whey is not transparent, unfermented milk is still present, and fermentation is not complete (the photos below show an easy way to detect the presence of whey).
Tipping the container sideways exposes separate layers of whey and curd.
The small sample saved as starter for the next fermentation faces the dual task of subduing rival bacteria, while at the same time fermenting a much larger batch of milk.
✅ Do:
- Allow adequate time for fermentation – one or two days should be enough in warm conditions
- Select a warm location, preferably away from doors and windows
- Lift the cover briefly to make a quick check on progress once or twice
- Use a sterile tasting stick or spoon to sample the ferment
❌ Don’t :
- Interfere unnecessarily with the ferment in the first 8 hours, apart from checks
- Move the ferment to a different location while fermentation is ongoing
What if there is no curd & whey?
If there is still no sign of curd after 2 days in a warm environment, the most likely explanation is that fermentation has not happened.
This may be the result of inactive starter or contamination (or both).
Harvesting
Before straining the harvest the ferment is ‘raw’ yogurt which when poured, moves like cream. Straining through a double layer of cheesecloth (stages 3&4) removes most of the whey, leaving a solid curd, plus a small amount of whey (which stabilises the curd).
The curd harvest should be over 50% of the milk used for fermentation.
Straining to remove most of the whey is common practise, however the disadvantage is that the curd is now more vulnerable to attack from airborne bacteria, and ages more quickly.
Many yogurt makers don’t realise that excess whey can be used as a starter, or in cooking (in place of water) to boost protein content.
✅ Do:
- Leave a small amount of whey in the curd – yogurt without whey has a rubber-like consistency
- Throw out any curd starter older than a fortnight
❌ Don’t:
- Put the harvest in old bottles (unless you know and are happy with their history)
- Leave the process half way through (eg. to answer a phone call)