Hi Dime...
It's been my experience that ultra pasteurized milk doesn't always say ultra pasteurized. You really won't know until you give it a try because there is no law (at least in the United States) that says the milk has to be labled as such.
Also, there is a huge difference between pasteurization methods used.
I spoke to a man that runs a commerical dairy about a week ago and here's some information he gave me.
According to this man (very nice and helpful btw) pasteurization occurs when milk is heated at a minimum of 162 degrees F for at least 30 minutes.
It can also take place at increasingly higher temperatures for accordingly shorter amounts of time.
UHT, or ultra pasterurzied milk is super heated to over 280 degrees F for about two seconds while other methods might use only 250 degrees for 3 seconds. Either way, this process completely destroys the milk as far as cheese making goes.
The milk that I have recently switched to comes from the dairy that I spoke to concerning the pasteurization process...
They heat their milk to 186 degrees F for about 10 seconds which although not perfect for cheese, the process doesn't completely destroy the milk.
According to the man I spoke with, anything over about 171 degrees does damage the milk (as far as cheese making is concerned) but he also said they used to produce cheese at this dairy using the exact same milk.
Well I tried some of this milk over the weekend and the curd did set up better than anything I've tried to date.
With all of the store bought milk I've used, I have had success but right away I could tell that this milk was different.
One thing that I think is interesting is that this milk comes from a prison owned dairy in Chester, Illinois and the reason that I decided to give it a try for cheese is because it is by far the best milk I've ever tasted.
They bottle their milk in half gallon glass bottles and the taste is out of this world. I'm really looking forward to seeing how my first Stilton tastes using this product.
I guess the only thing you can do is give different brands a try and see how they turn out. If a good pasteurization method is used, it should turn out a nice final product.
If you have trouble with your curd forming or if you get a really soft curd that falls apart upon stirring, this is a product to avoid in the future.
Our most popular brand (in my area) is prairie farms milk. Growing up, this was about the only thing you could even buy. Even though it is a tasty enough milk, it is not good for cheesemaking. You get a curd, but it is so soft that it is really tough to keep a curd throughout the stirring and cooking phases.
Hope this information helps.
Dave