Ive done quite a bit of research on the topic of solvent percentages, what proof of alcohol to use. It has been my conclusion that as long as you stay around the 30-60% region, that you your jow will age quite well. A few of the reasons are below…this get a bit complicated:
Alcohol is composed of 1 hydroxy group bonded to a hydrocarbon. Hydroxy is the OH molecule that composes 2/3 of a water molecule. When ethanoal and water are mixed, because its polar, its “visible” to the OH group in water molecules. This evidence suggests that a 50% mix of each is probably best.
However, while ethanol is an excellent solvent, it has a much lower dielectric constant than water (24.5 vs ~79), which means it has a significantly lower ability to separate ions from compounds than water does, and water is thus known as a universal solvent because of its ability to dissolve more substances than any other liquid. This evidence suggests that the mixture should be significantly more than 50% water and less than 50% alcohol.
Furthermore, water has a higher density than alcohol (1 g/cm vs about 0.75). When looking at volumes of water vs alcohol, there are more water molecules in a given volume than alcohol molecules. In equal concentrations, water molecules interact with the alcohol molecules and create hydrogen bonds between the two. When herbs are present, both will dissove the herbs and sometimes you may see this as various layers of material in your bottle of jow. When the water becomes saturated with other molecules, they will become mroe dense than the alcohol or water and layers on the bottom. For this reason, it makes sense to have more water once again, but this effect is negated by the fact that water molecules are more dense per unit volume than alcohol. Water can also hold more energy at the same temperature, which may help with lattice dissolving in the aging process.
Lastly, various herbs had varying molecules that it interacts with. For example, hong hua (safflower) has a variety of acids, a couple oils, and some sugars such as glucose. While this single example doesnt create a definitive answer, high school level chemistry labs easily show that many acids and sugars are completely dissoved in water, and only partially dissolved in alcohol, while many oils that herbs release are non-polar and will not dissolve into water or alcohol, but are only released into the jow because of the dissolution of other parts of the herb (also the acids may propagate as an aid in the aging process).
Overall, in my opinion, having a higher percentage of water than alcohol is desireable. When I make my jow, I usually top off each jug with water before remixing it and sealing it. My percentage is approximately 39% alcohol. Water is responsible for MUCH of the organic dissolving that takes place in nature, and alcohol to a lesser degree, as well as being a slight detergent. The main reason to have alcohol is to aid in dissolving some of the things that water many not be able to. The best approach would be to add a 3rd solvent that deals with more non-polar elements like some of the oil based jows available. I havent done this but as a part of my research am working towards determining if there is an increase in efectiveness with more than 2 solvents. My guess is it will be negligible, but we shall see. =)
Hope this was useful to some =)