Is there any reason for rennet not setting UHT milk?

Question

I am cheesemaking, but when I use UHT the curds are tiny and impossibe to separate from the whey?

Answer 1

It's because the UHT milk ceased to BE milk when it was being treated!

Answer 2

I believe the high temperatures used to create UHT milk has denatured the proteins... which results in tiny curds (clumps of proteins).