IMHO, bentonite is clearly misunderstood. Most likely, not understood because there are so many options to using it, the types of bentonite differ, how it affects both particulates, how it affects proteins for various amounts.
Ranges of bentonite can be from 0.5g/L to 3.0g/L. The effectiveness is directly related to HOW IT IS HYDRATED and THE LENGTH OF HYDRATION.
To directly answer your question, my best experiences to hydrate bentonite is just the opposite of what kit manufacturers have in their directions.
First, I estimate the what I will use bentonite for: proteins (aka, pectin) or for fining. If for fining, I leave it out, that comes post fermentation. If for proteins, I determine (guess) how much may be in the must. For grape/white wines, not as much as some country wines.
Second, I weigh the amount given in the kit. A recent 6 gallon WE white wine kit had 30 grams of bentonite.
Third, use established quantity guide lines from documented sources.
Fourth, I DO NOT USE HOT WATER and
hydrate for a minimum of 12 hours before it's aded to the must. Most instances I gently sprinkle bentonite in room temperature distilled water (about 100ml to 150ml) in a sanitized jar with an air tight lid. Then I shake the jar hard for 1 to 2 minutes. I keep it handy and mix/shake about every hour or so for about a minute and let sit overnight. If any small clumps remain after 3-4 hours, I use a spoon to smash against the side of the jar and shake again. The result when ready to add to the must is a creamy slurry with zero clumps.
As for the workings of clearing kit white wines, it appears that hydrating
effectively with 1/2 as much bentonite included in kits, produces less stripping of color, cleaner ferments, and retention of flavors. Yes, bentonite will strip color and flavors if used in excess!
For your reading pleasure, here are two sources of information:
Bentonite 101
https://scottlab.com/bentonite-clarification-heat-protein-stabilization
Fermenting on Bentonite
https://scottlab.com/fermenting-on-bentonite
Happy reading,
Barry