I have got the same annoying result a few times now, when making potato gratin, and something known as "french potato cake" in my country (grated potato in frying pan).

I believe that it's the potato which has a slightly off taste; bitter/metallic/raw. Some googling leads to solanine as an explanation, but I'm not completely satisfied.

Things that might be related:

  1. I rarely peel them (yet, I think that the same batch of potatoes, used a few days apart did taste fine the first time).
  2. I think that it's worse when any piece of potato isn't in direct contact with heat (i e the center of a thick potato cake or gratin)
  3. I almost always add raw, finely grated onions.
  4. Sometimes raw garlic - my impression is that it makes it worse.
  5. The potatoes are not green, at all, in any of these circumstances.

So my guesses are:

  1. Solanine, in that case solution is to peel them?
  2. Something related to oxidation, either in garlic/onion or perhaps catalysed by it. Solution, in that case?
  3. Rawness - can potatoes be soft and still be "raw"?
  • For solanine, you'll see a layer of green under the skin. You want to remove all of the green bits. You also want to remove the areas around sprouted eyes, not just the sprout itelf.
    – Joe
    Commented Dec 27, 2014 at 0:14
  • Oh, they're not green and don't have sprouts (updated question).
    – NiklasJ
    Commented Dec 27, 2014 at 0:25
  • Did you grow these potatoes yourself? If so, were they well-watered throughout the growing season? I've found that if I under-water my potatoes, they turn out somewhat bitter. I started growing my own because I ran across too many potatoes with a bitter, musty or chemical smell/taste, so if you have commercial potatoes, any of dozens of contaminants or additives could cause the problem.
    – Shalryn
    Commented Mar 31, 2016 at 19:21

1 Answer 1


My gut tells me that they are either under-done or need to be rinsed. Have you tried par boiling the potato? I would try slicing the raw potato, boiling for a few minutes to draw out some of the starch - then rinsing them before adding to your recipe. Worth a try I think.

Good luck!

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