Ok, I've been deathly Ill all week and am not quite over it yet... let's try this again, the way I had it originally, and the *correct* way:
250L juice + 2 plant remains ferments to 375L of bio mass, a 1.5 ratio. 40L of biomass distills to 25L of bio-ethanol, or a 0.3 ratio. Multiply them together and you get a total ratio of 0.45 bio ethanol out for every 1L of juice in. Thus, it is better to just ferment the grape juice into 0.5L of wine and to hell with the remains.
You are absolutely right. If you are looking strictly at power obtainable from the grapes, wine is your best bet. However, you still end up with the remains. Even though you *could* turn the grape juice into fruit juice instead, to make biomass, this isn't the best method. Instead, you take another liquid you have excess of like honey or honeydew (which cannot be turned into power otherwise), and use that to process the remains into biomass. 40L of biomass can be turn into 12L of ethanol at a cost of 384GU. Or, it can be turned into 24L of methane gas for the same cost. (BTW, how did you come up with 40L of biomass to 25L of bio-ethanol? I couldn't find this formula anywhere.)
For easy math, I am going to assume starting with 200L of biomass (5 processes @ 384GU ea--1,920GU total).
1L of Ethanol produces 144GU.
5L of Methane Gas produces 384GU.
Putting this all together gives:
Ethanol - 5 x 12L = 60L * 144GU / 1L = 8640GU - 1920GU = 6,720GU net.
Methane Gas - 5 x 24L = 120L * 384GU / 5L = 9216 GU - 1920GU = 7,296GU net.
So, if you are processing remains, their best use is to convert into Methane Gas.
Once you are sufficiently industrialized though, it is even better to convert the biomass into glycerol, then into glyceryl and add it to gasoline to convert to nitrofuel. You use a renewable resource to extend the supply by 25% and power output by 50% of a non-renewable resource.