Can't use apostrophes in ingredient names

Can't use double quotes either - which are sometimes used as an abbreviation for inch

This happens on line 963:

if (check_plain($ingredient->name) != $ingredient->name) {
  form_set_error("recipe", t('Ingredient names must be plain text.'));
}

and is due to the fact that check_plain() actually converts the text so that $ingredient->name in many cases will be renamed.
A work-around could be to strip off ' and " before running through check_plain() (and on the other side of the != as well, of course), though there are probably better means.

Yes, it makes it hard to even specify brand names at all. Try escaping the apostophe (use \').

Turns out we don't really need that check at all. I've removed it now (in 4.7, 5.x and HEAD).