The Food Lab: Better Home Cooking Through Science

coming out of plain water made very little difference in
terms of flavor penetration. So, you might as well just add
the vinegar to the potatoes after they’re cooked, right? But
there’s actually a very good reason to add a little vinegar to
the potatoes cooking water: it helps prevent them from
overcooking, something we’ll see again when exploring
French fries in Chapter 9 (here). Pectin breaks down much
more slowly in acidic environments. I found that adding a
tablespoon of vinegar per quart of water to my potato pot
prevented the potatoes from becoming mushy, even when
slightly overcooked.