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The yoghurt I bought from the store in a 1 l glass jar has in the 4 or 5 days since opening separated a little from the whey. The whey is has gone slimy putting me off breakfast.
On this site it has been stated several times that yoghurt cannot really go off. However, this has happened a few times with this brand and I'd like to know what is causing it (and if its really safe to eat)
It smells like yoghurt and the packaging says it is made with pasteurized milk.
It's probably thickeners, such as carrageenan or xanthan gum, which are thickening/sliming up the whey. Draining off the whey or stirring it back in should be fine. A brand which doesn't have added thickeners (look for "strained" or "Greek-style" yogurt, then read the ingredients) won't do this.
I've had yogurt go off many times, and slimy whey isn't how yogurt goes off. The whey is nowhere near as tempting to microorganisms as the yogurt solids, so you'll see mold (or whatever) on the solids first, not the whey.
Some yoghurts do release a little whey. The one I was eating the other day even said so on the packet, and that it can just be stirred back in.
However if the whey has since gone slimy I'd be a little more concerned. Certainly if there's any sign at all of stuff growing on it you should get rid of it. If it sits out on a breakfast table for some time, that can encourage it to spoil compared to serving some and returning it immediately to the fridge. You may want to buy a smaller container next time. Yoghurt can go mouldy, though not quickly or easily, and smell isn't necessarily a good guide.
You need to decide how confident you are - if you're unsure there's no point risking it, or even risking a day of worrying after eating it. I say that as someone who hates wasting food.
