Tell-Tale signs of fermentation
During fermentation, milk is used up and replaced by white solid curd covered by a thin layer of watery whey; the photos below show an easy way to detect the presence of whey).
Tipping the container sideways exposes the whey layer
If the whey is not transparent, then there is still unfermented milk, and fermentation is not complete.
Saving a small sample in order to start the next fermentation (stage 5 of the 5-stage process) ensures future fermentations but faces the dual task of subduing rival bacteria, 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, draught-free conditions
- Use a sterile tasting stick or spoon for sampling the ferment
- Lift the cover over the bowl once or twice to make a quick check on progress
❌Don’t:
- Interfere unnecessarily with the ferment in the first 8 hours, apart from checking the progress of fermentation
- Move the ferment to a different location while fermentation starts
- Use the same tasting stick more than once.
What if there is no curd & whey?
If there is still no sign of curd and whey after 2 days in a warm environment, fermentation has not happened.
The most likely cause is an inactive starter, poor environmental control (eg temperature well below 20 degrees C) or contaminated milk.
After the harvest
After harvesting, it is customary to strain the raw product through a double layer of cheesecloth (stages 3&4 of the 5-Stage Process), which removes most of the whey, leaving a solid curd, plus a small amount of whey. Removing all the whey however is inadvisable as it affects the texture and makes the curd more vulnerable to attack from airborne bacteria.
The curd harvest should be around 50% of the milk used for fermentation.
Many yogurt makes don’t realise that excess whey can be used as a starter, or in cooking (in place of water) to boost the 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 one week.
- Experiment using whey in place of water as an ingredient when cooking
❌ 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)
- Be tempted to manually squeeze out remaining curd in the straining process.