I am new to making homemade ice cream. I just started to feel confident with plain vanilla, so it was time for the next step - adding fruit.   The custard recipe says it can be turned into fruit ice cream by adding 30g pureed fruit per yolk. I looked into the basket for a fruit likely to make a good puree, and settled for a honey dew melon. I made the custard base (yolks, cream and sugar with a pinch of salt), and, because I wanted more fruit taste, made 50g of melon puree per yolk and thickened it with a bit of guar gum, because I feared crystals from the rather liquid melon. I added the melon to the prepared custard, it wasn't exposed to heat.   After chilling and transferring to the freezing plate, I indulged in licking the thermometer, spoon and bowl used for the making of the ice cream. I was unpleasantly surprised at the lack of melon aroma and strong bitter taste. It was as if I was chewing the seeds of the melon, although there were none in the ice cream, I am sure I'd have seen them if they had fallen into the puree. Combined with the overbearing sweetness of unfrozen ice cream, I thought of throwing the batch out. But I froze it anyway. Frozen, there is much less bitterness (and of course much less sweetness), it tastes as if I am eating a raw gherkin. In fact, if I didn't know that there is melon in there, I probably wouldn't have recognized. It is eatable, but not especially good.   The aroma problem was solved when I ate a piece of the melon: this exemplar must have grown in a dark greenhouse. It was watery, only a hint of sugar content, only a hint of aroma. But it wasn't bitter, just tasteless.   But I am still wondering what went wrong. Does melon react with guar to create a bitter compound? Does melon react with cream to create a bitter compound (I know kiwies do, but melons?) Was there so much heat in the custard base as to cook the melon, and does cooked melon taste bitter? Would a better melon have made a difference, or would it have been bitter, sweet and aromatic at the same time? Is melon generally unsuitable for making ice cream?  
This is about a melon-milk shake that I made previously. I don't know if it applies. Melon has a reaction when mixed with milk which causes the taste to become bitter. When freshly made it tastes okay, but when left for some time (a few hours) it gets bitter. 