Bitter lettuce

Last fall I grew 4 kinds  of lettuce in my garden.  It was all so bitter no one wanted to eat it.  When it was time to replant that bed come spring I did the chop and drop.  One of the variety's grew back.  It was still very bitter.  I did another chop and drop yesterday.  If it continues to grow back when the weather is cooler will the lettuce become eatable? What makes it better? I watered it like crazy this fall, that didn't help.  I'm just trying to decide if I should continue to chop and drop, or if I should pull it up at some point so I can plant a lettuce we will enjoy.  I am amazed it is still growing in our hot California sun.  I just wish it tasted better. Thanks happy growing.

Sounds like it has bolted from heat.  Is the stalk big? If so it is too hot.  Provide partial shade and make sure it doesn't get up to 80 degrees.

In addition to the above comment, too little water can be a factor.

Also the type of lettuce is important.  Look for "tough" varieties like romaine or deer tongue.  Avoid "wispy" types such as buttercrunch or bibb.

If your soil is poor and the lettuce grows slowly, that can make it bitter, too. You want rich, moist soil so the lettuce grows quickly and stays sweet. If you've got hot sun on it, that won't help either. I very rarely can grow nice lettuce cause our "spring" goes from too cold and wet to grow anything to really hot so quickly.

Mostly what I would like to know is if I keep chopping and dropping this bitter lettuce, come fall and winter when it isn't so hot will it become sweet if I water enough? The kind of lettuce is a mystery, I doncumented my summer garden but not my winter for some reason or other.  Anyway all I can tell you is it is a light green leaf lettuce. The only one out of 4 variety's that continues to come back.  I just don't know if I should continue to chop and drop, or pull it out by the roots.
I don't have the money to test my soil, but I have done all I know how to do to have wonderful soil.  Last fall I made this raised bed a hugel beet.  There is lots of organic compost, some of my compost, blood meal, bone meal, worm castings, alfalfa meal, azomite, Down to Earth Bio-Live 5-4-2 ( beneficial bacteria and mycorrhizal fungi) I think I also had some 5-5-5 organic fertilizer. Basically Mostly compost with a little of everything I had on hand. All this was mixed with some of the native soil.  Since planting I have added Humic Acid, and some oyster shell near the pepper plants. (One of my pepper plants keeps getting blossom end rot. My thinking was a little extra calcium, and the Humic Acid will make the calcium available to the plant.)  I have also been using compost tea 1 to 2 times a month.  So I think, or hope this is a pretty fertile bed that will get better as the wood inside begins to decay.
Thank you everyone for your input and helpful comments.

Sounds like the soil is ok. Too much sun and not enough rain causes bitter lettuce. Wait for the wetter fall season with cooler nights, maybe add some shade.
Most people if introduced to the bitterness slowly get used to it, enjoy it and then find rapidly grown lettuce bland. It's all what we are accustomed to.