Pre mix drink mix storage powder vs liquid

Like many of you, I make my own drink mix using a proprietary recipe (Maltodextrin, fructose, caffeine, beet powder, and a ground up presta valve cover from MVDP’s race bike). Mixing it every day is a hassle, so last year, I mixed the powders in an air tight container so I could simply dump in the proper number of scoops before my ride. However, I was never 100% convinced I had the powders mixed uniformly through the container.
If I were to simply mix a pitcher of drink mix, I could be more confident that my proportions were consistent (albeit at the expense of mixing once a week instead of once every few months).
Is there any reason a pitcher of drink mix in the fridge would go bad over the course of a week or two?

It may be placebo, but in my experience, drink mix always tastes a little off after more than a day of being mixed… Its not terribly uncommon that I’ll have half a bottle left from a trainer session, and I’ll typically refrigerate it and use it the following day. But having done so for more than over night and it just never seems to taste right. I’ve never stressed about getting the powder ratios perfect, as its pretty low consequence if they’re a few gram out of balance, especially if you’re well below the 120gm/hr zone… If thats really a concern, maybe mix your important race day bottles individually, on a scale.

I mix my mix with liquid once a week and keep it in glass containers in the fridge. Then I just add to bottle, top off with water, and I’m good to go. As you say, this makes sure that the mix is actually in the proportions I want, and it saves me time during the week.

Each week I load five 1-cup plastic containers with my mix for the week. I just dump each ingredient into the cups individually. Takes about 5-10 minutes.

I then transfer the pre-measured mix into my bottles the night before a workout using a plastic food funnel with the narrow end cut off, mix with hot water, then store in the refrigerator over night.

I mix up very large amounts of powdered drink mix at a time ( up to 10 pounds at a time) using an industrial sized mixer I run the mixer for about fifteen minutes to ensure pretty good distribution. Once this is done I use extra large freezer bags into which I put two pounds of powder each. These then go into my freezer with one remaining out.

I mix up four bottles of drink mix at a time and store them in my fridge ready to go I refill the bottles as needed and wash them once per week

Does this guarantee that I have the exact perfect ratio of ingredients in each bottle….Nope! Am I a professional Athlete….Nope! Does this give me some extra time to play with grandkids….Yep