blackened carrot cake I have a favorite carrot cake recipe that I have made many times.  it is always beautiful and tasty (although I am sure some would debate that since it contains pineapple).  However, that last two times I made it, it went into the pan looking normal, came out looking normal, and within 3-4 hours it turned a very dark grey, almost black even.

I am guessing that there was some sort of chemical reaction going on involving the pineapple.  i used a different brand than usual while everything else stayed the same.  I will say I haven't yet tried switching back to the original brand of pineapple to see if that solves it (haven't had a chance, but a good scientist - which i am not - would do that pronto).

The contents are :
2.5 C whole wheat flour
2   C brown sugar
2   t cinnamon
1   t nutmeg
1   t cardamom
2   t baking powder
1   t soda
.5  t salt
1   C chopped walnuts

4     eggs
1     egg white (or just another egg)
3   C shredded carrots
2   C crushed pineapple, with juice (no measure on the juice, just "some")
1   C veg oil
2   t vanilla

Anything there the pineapple would be reacting with?  And why oh why would it be great for many years and then start turning so sickly looking?
Two things come to mind 
     1. Do you peel your carrots?
     2. Metal pan reaction .
Try peeling your carrots.  I have gone as far as cleaning my fresh carrots with a green scrub pad. But have found nothing works as well as peeling them. Even if you never peeled them before, when you said you did not have this problem, It could be a reaction to something thats being "added" to the carrots now days.
The other thing I had a problem with in the past was the type of pan I used. I found that some metal pans would discolor my cake. And the longer the cake is left in the pan it would effect the flavor as well.
Hope this helps someone. Have a great day!