Organic milk or what?

The fact that the milk is organic will have nothing to do with it. To put it simply organic simply means that the cows have eaten food, grass and silage, grown on land that has not been fertilised with inorganic fertilisers and that the cows have not been routinely given antibiotics.

I routinely cook with organic milk and I have never had any problems at all.

minimoon when we were young we probably did have organic milk, because farmers then did not routinely use fertilisers on pasture, beyond that produced by the cows themselves nor were antibiotics routinely fed to cattle.

The organic label and standards only started being publicised and marketed as such when milk production became industrialised in the 1970s and 1980s

I'm going to make another with ordinary non organic milk, and see what happens.

The consensus seems to be overheating or heating too quickly.
www.thespruceeats.com/prevent-milk-from-curdling-when-cooking-996067

When the children were little we didn't have organic milk. I wonder if that was the reason for the curds and whey? DH has just told me that a lady who works with him used the same kind of milk for cakes, and she had to throw them away as they were spoilt.

It's pasteurized and homogenized, fresh as can be. Oven at the usual temperature. In fact when the children were little I used to cook it in the Aga and it never split.

Is the organic milk pasteurised minimoon?
If it isn’t, it may contain bacteria like some natural yoghurts do.
It may be that when you warmed the milk and added the sugar, that got the bacteria going and caused the separation?
I’m just guessing and will be interested to hear what others have to say.
The other cause could be your oven was too hot. Possibly!

It was new milk, only bought last night with the use by date of 10th Nov. My fridge is cold enough too. I know the milk isn't off, or on the turn.

I think it’s more likely that the milk was not as fresh perhaps? Do you keep the milk in the fridge door or further back where it’s colder?
I find that milk bought in one local supermarket seems to last longer than the milk from a different supermarket despite buying them on the same day, so I stick to one specific supermarket for my milk.