Someone help me to understand why you use isopropyl alcohol to titrate and not methanol. Thanks...

If you have ISO that is at least 90%, it has two advantages that I know of:

1. Oil dissolves in it much better, so the titration can work

2. It is relatively non toxic for using in and indoor setting with an open jar.

Less than 90%, like the 70% from some drug stores does not keep the oil suspended as well so it may lead to inconsistent results and or error.

Also, WVO doesn't mix well with methanol. IPA is really a better solvent. It absorbs more water than methanol, too. Which is important if you have high titrating oil and are adding a lot of titrating solution. HTH

That all makes sense but now another burning issue (in my mind) makes even less sense: Why not use ethanol alcohol to make the fuel instead of using petrol-based methanol?? You could conceivably make your own ethanol for biodiesel production. From what I understand, methanol is simply ethanol which has been poisoned to prevent use as a beverage (mainly because of taxation laws). Is there some reason that ethanol wouldn't work for making B100?

Yes, ethanol works to make BD. You would then be making ethyl esters instead of methyl esters. Few things, however. Yes, you can make your own ethanol (as many a moonshiner will atest) BUT, you cannot make ANHYDROUS ethanol. The best reflux still will give you 95% EtOH. The other 5% is water. Water is killer in the BD process, especially with EtOH. Ethyl ester BD is a much more finicky process. Any number of small errors will give you glop with EtOH, but not really affect the MeOH process. Lastly, methanol is not poisoned ethanol. Denatured alcohol (which you can buy in many stores) is ethanol that has been rendered undrinkable by the addition of another product. Many times it is methanol or gasoline that is added. EtOH is also a much better solvent than MeOH. I made some batches of BD with E-85 fuel (85% EtOH/15% gasoline). The reaction went well, but the glycerine did not drop out. The EtOH kept it in solution. Came out when washed, but was a REAL hassle. There is a method here called the Masters formula, by Oil Can Harry, that reacts it in this manner, then just uses it all as fuel. He doesn't separate the glycerin and doesn't wash. Hope all this makes sense and Welcome to the forum!