Methanol vs ethanol: Methanol or ethanol can be used to make biodiesel, but although ethanol is less toxic, it has to be used in it's pure form (100%), and this is more expensive to obtain. Generally, commercial ethanol is only 95% pure; the remanining 5% of water must be removed using a chemical process. Also, when using ethanol, the oil being processed must be extremely dry (free of water). This is difficult to achieve, especially in used oil from restaurants which is used for frying vegetables, meat, or fish. Methanol is much more forgiving in terms of water; it is still best to use oil that is as free of water as possible, but a little water will not ruin the reaction. It will result in the production of more soap, and may hinder the biodiesel reaction some, but you can still produce good quality biodiesel.

Lye (NaOH) vs. potassium hydroxide (KOH): Lye, also known as caustic soda, is cheaper and generally more available, and is a little easier to handle because it is granular (like salt). KOH, also known as caustic potash, has several advantages. One is that it dissolves faster in methanol. The second is that the glycerin byproduct produced is less toxic to dispose of, since potassium is a nutrient for soil, whereas the sodium in lye is toxic to soil. Finally, the glycerin produced remains very liquid, even at cold temperatures, whereas glycerin produced from a lye-catalyzed reaction gets semi-solid and can be difficult or impossible to pour, especially at cold temperatures.

Phenolphthalein vs tumeric vs phenol red: These are all pH indicator that can be used in the titration to determine free fatty acid levels in the oil. Phenolphthalein is the most accurate, because it changes color strongly at a pH of 8.5. Tumeric is next best, changing color a little sooner, but still around pH 8.0. This pH indicator is made by simply mixing some powdered tumeric with some isopropyl alcohol. Shake it up, and let it settle overnight, then decant the clear liquid from the top. Phenol red is more available at pool supply stores, but it changes color too early (at a lower pH), and is therefore the least desireable choice.