here's some stuff I found online...
from Protein Factory...
Q. I use your CFM Whey Isolate very frequently. Is it okay to premix 5 or 6 scoops with water, store in a thermos, and drink at intervals throughout the day? Would the premixing degrade the quality of the protein in anyway? If not, what would be the longest amount of time that CFM Whey Isolate could sit in water without losing its quality? What about the Micellar Casein, does premixing and storing in water effect its quality?
A. Once you mix ANY of our protein with water you create the environment to grow bacteria. Treat the drink exactly like you would treat milk. If you leave it out of the refrigerator it will start to grow microbials. I cannot give you a time line, but I recommend you keep it in the frig. Premixing does NOT degrade the protein either or effect it quality.
and this from AST...
Q: I consume about 5 VP2 shakes a day. I have been premixing them with water in the morning into a single container and drinking it gradually throughout the day. Does the premixing with water change or affect the quality of the protein? If not, would premixing the protein with water and storing it for a week affect the protein?
A: I'm not crazy about premixing supplements. There are some types of supplements that it is absolutely forbidden to put them in a liquid for extended periods of time. Creatine is certainly one of these supplements. Glutamine is another. Shakes with added vitamins and minerals should not be premixed for very long before drinking either.
VP2 Whey Isolate is a hydrolyzed whey isolate that is produced in a very unique and specific manner. It's comprised completely of native protein fractions that are not adulterated with other nutrients. This being the case there should not be a problem premixing VP2 the way you are doing it. I wouldn't however, recommend keeping it in solution much longer than one day at a time before drinking it. I can't say that there would be a problem for sure but I also can't, with all certainty, say there would not be a problem.
VP2 is the most effective protein available for delivering muscle building nitrogen. It also provides certain functional properties not available in any other protein. To date no research has been performed on its extended stability in a liquid. Because of the lack of research in this area it can only be advised to limit its extended stay in liquid to hours and not days.