Nobody is saying that that’s the ideal (or even remotely reasonable) ratio of yolk-to-oil. Just that the lecithin in egg yolk is such a good emulsifier that the yolk will disperse evenly in a colloid form throughout that volume of oil. (ie; you have a lot of wiggle room with how much oil you can add to the recipe before you end up with an unstable mess.)
You can add litres and litres of oil to an egg yolk and still get a perfectly fine emulsion – but much more than a cup or so, and you’re getting further away from what people generally expect of an emulsion sauce.
Yes. Fresh mayo doesn’t have a particularly long shelf life. I try to use it within a week. I make it with 250 ml oil (usually a fruity olive oil, such as Frantoia. Sometimes I extend it by using a 50/50 ratio of Frantoia and some flavorless oil like canola or soybean) per egg yolk. I then mix in a tablespoon or two of lemon juice (I prefer it to vinegar), sometimes a little powdered mustard and/or paprika and/or sugar. I never add hot water.
The actual quote is in “The Curious Cook” and I believe the updated 2005 version of On Food and Cooking also contains some more information. Unfortunately, I only have the old, 1980’s version of OFaC on me so I have to go by indirect references: this site says 6 gallons. this site says 25 quarts.
I also remember hearing that freezing the yolk and then thawing leads to substantially better emulsification although nobody knows why.
Also, due to the emulsifiers present in butter, a single egg yolk can make something like 160L worth of hollandaise or something equally as absurd.
An emulsion is a colloid - specifically, of one liquid in another. Other types are:
Aerosol: solid or liquid in gas
Foam: gas in liquid
Solid foam: gas in solid
Sol: solid in liquid
Gel: liquid in solid
Solid solution: solid in solid (a frozen emulsion, if you like)
There’s no “gas in gas” colloid, as gas mixtures are already as finely divided as you like.
