Sur un forum américain, la question a été posée à 3 fabricants de protéine :
this from t-nation ;
Q. Hi guys. I have a question about premixing meal replacements. I'd never worried about this until I noticed that my Designer Protein container says to mix and drink immediately. Because I live about half an hour from the gym, I like to mix my shakes before I leave so I can drink them immediately after a workout. And when I train at school, I have to mix it in the morning and not drink it until the end of the day. (I don't get home for at least an hour after training.)
So I was just wondering, approximately how long can you leave a shake in a thermos before it goes bad? Does it even go bad at all? I've noticed that a thin layer of Myoplex residue in a glass looks like onion skin after a while.
My shakes are either Designer Protein and maltodextrin, or Myoplex and maltodextrin.
Chris Cappadocia
PS: Thanks also for all the very valuable (and free) information!"
A. Chris, as long as you keep your thermos and protein shake relatively bacteria-free, and the temperature cool, it should last several hours. The biggest reason Designer Protein (or any other company) suggests drinking a shake immediately after making it is because of the taste. Most shakes are at their best soon after mixing.
If you're going to prepare an MRP or protein shake in advance, like you say, you should probably make it thinner by adding a little more water than what's recommended. Shakes tend to thicken over time.
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and this 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.
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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.
