Fermentation Support Forum

Hi, when I leave yoghurt out of the fridge for a few days I notice it goes sour. Is this fermentation in action? What effect does this have on the nutritional composition of the yoghurt? Ie does this decrease the carbohydrate content, increase the protein content etc?

Is this yoghurt you made yourself?

I understand it to be that at room temp the fermentation process continues and uses up more and more of the lactose from the milk. The yoghurt gets less sweet, and because it's a lactic ferment, it also gets sour. I don't have a fridge and find it takes a while for commercial yoghurt to get past where I can eat it, but I quite like a sour yoghurt to start with.

thanks its store bought yoghurt

When your left-out yogurt goes sour, it is the action of microorganisms doing their thing in the yogurt. If the process is appealing and safe, it's fermentation. If it isn't, then it's spoiling.

I don't know about the effect on macronutrient distribution.

I read somewhere (I'm trying to find the link but can't I'll post if I do) that because store bought yogurt usually has some kind of preservatives or additives in them the culturizing is VERY weak and by leaving it out before the culturization can start the rotting takes over faster so I'm guessing it's spoiled...I don't think you should leave store bought yogurt out of your fridge. You can try heating it and making another batch of yogurt but with room temperature I think all it'll do is rot?

Store bought yoghurt is almost certain to have a low bacterial count due to them requiring it completed as quickly as possible for commercial and profit reasons.

Home made yoghurt is always going to be far superior unless you really screw it up. By all means begin by using a store purchased yoghurt as a starter and begin from that and then culture that for further fermentations as it should provide a superior result with a higher bacterial content.

I have used capsules eg 5 billion CFU as a starter and found them to take around 12 to 14 hours to complete a set and firm yoghurt and by comparison using just a 1/3rd of 200ml pot to start the next batch of 7x200ml pots completes in around 3 to 4 hours! To me that indicates just how much stronger my yoghurt is as the number of CFU must be substantially higher. I have seen capsule manufacturers claim that their capsules are much stronger than commercial yoghurt. Maybe, but it's laughable to suggest that they are stronger than home made yoghurt.