One Alchohol Card per Sugar Card?

[Uncle Bingo]

Hopefully this wasn't dealt with elsewhere.

The video tutorial and the quick and dirty rules both say that an alcohol card should be played with each sugar, my regular opponent and I don't always do this, but also get some awful tasting hooch. Is this practice merely recommended or is it an actual rule?

Thanks

[Paddles]

Yes, it is an actual rule. From the rulebook, page 11 (Distill phase)

Once you’ve added your ingredients to your washback, follow these steps to distill a spirit:

1. Add one alcohol card to your washback for each card in the central, sugar slot of your washback.

BGA puts these in for you automatically. If you're playing on a board, I'm not sure why you wouldn't put these in - having them in improves your probability of not losing a sugar card that you need to make the better spirits (more victory points), and each one will either increase the money you get when you sell the spirit, or become available to substitute for yeast or water in your next distill.