Bentonite is a negative charged, clay-like mineral, that, like sparkalloid, removes positively charged particles. It works best when the wine is at warmer temperature so we suggest clearing with bentonite in the late spring or early summer. It is also more effective at a lower pH because the positive charge on proteins is stonger at lower pH levels.
Generic low level fining for five gallons: blend 1/2 tsp (approx 3g) with 1/2 cup of hot water (140 to 200 F) in a blender for 1-2 minutes. Let stand for 60 minutes, mix, and stir into wine. Let stand for 10-14 days and then rack off. This is fining at .16g/L
For a generic mid level addition: Follow above directions but use 9 grams of with 3/4 cup of water. This is fining at .5g/L.
A more scientific method is to make a stock solution of 5% bentonite and then run bench trials to see the lowest level that solution that will clear the wine sufficiently. Fining is non-selective so at the same time you are removing yeast you are also removing other desireable phenolic compounds. Thus the lowest level concentration that will do the job is always the most desired. To make a 5% solution add 50 grams to 850ml of hot water and mix it thoroughly, then top off to a final volume of 1L. You will need to set up a trial with clear jars of the same volume. Add different amounts of solution to achieve addition rates between .3g/l and 2.0g/l. You will have to do some math! Let the trials clear overnight. For more technical information check out BK653 - Monitoring the Winemaking Process from Grapes to Wine - Techniques & Concepts.
When making a wine kit from concentrate you will often add the bentonite on the first day. This happens for a few reasons. It is used as a nucleation sites for the removal of CO2. Additionally, the bentonite is moved all around the wine by the CO2 and thus less can be used more efficiently in a shorter time period.