yogurt

Some yoghurts are heat treated to give a longer shelf life. This kills off all bacteria, including the friendly ones. Mar st big commercial brands are heat treated. The sell by date will give you a clue if the label doesn’t.
Live yoghurts will only last a week or so before bacteria growth makes them unpalatable.

I buy the occasional small pot of plain yogurt as a starter for making my own yogurt. None has ever failed so I assume they are live even though it doesnt say so on the container.

Same as Sue- I’ve often bought ordinary yogurts, plain or flavored, to use as starters and they’ve always worked. Just look at date - expiry should be as far ahead as possible so that more bacteria will be alive. I look at ingredients and avoid ones with corn starch as “stabilizer”. These are less likely to be proper yogurt.

I only buy natural yoghurt with live cultures. It says on the pot. No point in using any other.