Mysterious bitter taste from tropical fruits and coconut I cook every day, and today I had an experience I am at a total loss to explain. I am hoping the combined knowledge of the Internet can help.

Today, I decided to make a  tropical fruit custard. Being as it's passover, it contained matzoh meal. I blended the ingredients together, and it tasted fine--a little bland, but fine. I sprayed a casserole dish with canola oil, and poured in the mixture. 30 minutes later, I test it for doneness with my finger, then taste the batter on my finger. It was BITTER! Not curdled milk, not sour, not anything but overwhelming bitterness, like I was chewing on the pith of a grapefruit. 

I ate some raisins to cleanse my palette, drank a glass of water, and tried again with a spoon. BITTER. I called down my fiance, who loves this sort of thing. (I was making it for her.) She made a face and said "bitter!" In three letters, WTH? Any help would be very welcome.


2 cups Goya frozen coconut
1 cup frozen mango
1 cup frozen pineapple
1/2 tsp Vanns Spices coconut extract (propylene glycol base)
1 tsp homemade vanilla (Madagascar beans, vodka base)
1 cup matzo meal
1 cup Breakstones lowfat cottage cheese
1 cup Wegman's egg white
1/2 cup Fage 0% greek yogurt
1/2 cup Breakstone's lowfat sour cream
2 tbsp sugar
1 tsp molasses


These are all ingredients that I use routinely, with the exception of the Vanns. None of them are particularly bitter. (Molasses is slightly bitter, of course, but nothing like this.)

I had cleaned the casserole dish two days earlier, dried it by hand, and put it on the shelf. I washed the pan with soap and a scrubbing pad. Its preceding use was in roasting tomatoes. Burnt tomatoes can be bitter, but not like this, and anyways, it was pretty clean. It definitely didn't taste like soap. 

Does propylene glycol have some kind of reaction where it can turn into hell bitter juice? What else can it be?
The culprit is the pineapple.

Raw pineapple contains bromelain, an enzyme that breaks down the protein in your milk, making it bitter. The same principle is applied when bromelain is used as meat tenderizer, either as powdered additive or as fruit-based brine.

This process takes a short while, so if you used pineapple in your cereal and eat it right away, it will not be bitter (unless the enzyme content in your fruit is excepitonally high), but after 30 minutes it will be noticeable.

Bromelaine will also keeping gelatine from firming up. Heating destroys the enzyme, so canned pineapple is perfectly "safe".

Other fruit with similar properties are papaya (papain) and kiwifruit (actinidin).

This article explains it a bit more in detail.