The Jungle Juice recipe that I have used in the past was made up of something like 5 cups of maltodextrin, one cup of fructose, one cup of glucose and a tablespoon or less of diet salt (which has potassium chloride included to bump down the volume of sodium chloride).
It was almost tasteless, and the basis of the mix was that the glucose as a short-chain carb molecule was processed and used first; the fructose took a greater time to break down and therefore was an intermediate fuel; and the maltodextrin, as the longest carb molecule of all, provided the long-term energy input.
There is some caution needed with the salt. The diet salt variant has a much stronger taste than ordinary salt, so there might be a need to start at much less than a tablespoon's worth and work up from there.
The one thing I didn't do was mix in flavourings except as a minor experiment with Crystal Lite stuff, but it didn't seem to work that well for me. The Jungle Juice mix does have a sweetness to it, brought on by the fructose. I rather like the coffee flavoured HammerGel, and I've been tempted to get back to mixing up a batch or two to see if I could replicate the flavour.
Another variant is to mix in a little whey protein powder, but there are issues with is not dissolving, but rather remaining in suspension. The protein is more worthwhile, however, for longer distance rides, say 300km and over.
And all this is in the context of a randonneur for whom the cost of energy can climb rather rapidly if relying on commercial products.