Grow Your Own Bitter lettuces?

There are many chemicals in the veggies which make it bitter. Here it goes, lol, a long and boring explanation, for those who are interested

Some bitter compounds are lipophilic, which means they are capable of dissolving in oil. Cruciferous vegetables, such as mustard greens are bitter. Sometimes, riping makes something bitter, like in fruits, when a riping compound is produced.

The acidity of the soil, the lack of water in soil, can cause bitterness in some veggies, like carrots. Younger veggies are less bitter than older ones.

More bitter components in veggies: phytonutrients ( a type of antioxidants), including glucopyranosides like salicins, some flavonoids and polyphenols, most antioxidants, antipyretic ones, limonin, ... and I must have forgotten a few.

Thank you, Pigjes! I'm sure it's heat/lack of water that have made them go that way (the Bibb lettuce, at any rate). Is it still OK for them to eat?

Arugala isn't the best to give them often but I'm sure if the rest is a little bitter it won't bother them much.