why can potatoes turn black if used in a scalloped potato dish prepared the day ahead

Why can potatoes turn black if used in a scalloped potato dish prepared the day ahead?

I made a delicious scalloped potato recipe for Easter. It has fennel slices, crushed fennel, Gouda cheese, cream, and half and half (not lo-cal!). I prepared the dish on Saturday, covered and refrigerated.

When I took the potatoes out of the frig to bake on Easter, about 1/4 to 1/3 of them had turned black!! I’m certain I made this same dish last year, with no problems.

I know that potatoes will turn colors upon peeling and slicing if you don’t either put them in water (which I did while I as assembling the other ingredients), and/or move rather quickly.

The potatoes were slightly cooked along with the fennel in the cream sauce in a non-stick skillet on top the stove before layering with the cheese in the pyrex baking dish.

I covered them with the casserole lid (not foil), but there was air between the potatoes and the lid. Could this have done it? Did the fennel do it? Thanks!

Scalloped potatoes are so delicious! I know how disappointing it is when you want a tasty dish, but also a dish with a really nice presentation.

As I was reading your question, you mentioned that at least 1/3 of the potatoes turned black, even though you prepared the same dish last year and everything was fine. What I can tell you is this: don’t blame the fennel.

The following could have caused your potatoes to turn black, so let's see:

1- Usually, potatoes can turn black when they make contact with an aluminum or iron pot while cooking. You mentioned you used a non-stick pan for cooking.

2- You also mentioned that, even though you covered the potatoes with the lid, there was air between the casserole and the lid. It is highly recommended to cover the potatoes with a tight-fitting lid.

That is because if potatoes aren’t covered completely, they are going to make contact with air and, while cooling, they will slowly begin to get a dark color.

3- But, since you said that you covered the potatoes with a cream sauce, I think we can finally know what really happened.

It is possible that you cut your potatoes so thin, and your cheese sauce was so thick, that 1/3 of the potatoes remained uncovered by the sauce.

Since the lid wasn’t tight enough, some air made contact with the uncovered potatoes and they turned black.

4- Maybe, last year you used a different pot, or a different baking dish; maybe last year you covered the potatoes completely, and this year the sauce didn’t cover all the potatoes evenly.

5- It is also possible that last year you used a different variety of potatoes.

Next time when you cook scalloped potatoes, I’m sure everything will taste really good, without potatoes turning dark again!