Hum, I'm not sure about the bitter if you cut it off when it starts to bolt.

Yes, soaking lettuce in cold water will help against bitterness. At least I find if I take a bowl of water with some ice in it and dunk the lettuce as I cut it, it helps not only wash but cool and leach out the bitter laytex.

Lettuce is a cool weather crop which is why I grow it indoors here in Florida since it is too hot for it most of the year outside. Even so, the lettuce I have growing indoors does eventually bolt anyway as I'm too cheap to run the AC that cold so it is probably 80 F under the lights.

I'm having this issue now, does anyone know if keeping a fan on the plants helps? I have a fan on them, but only keep it on about 3 or 4 hours a day. Or maybe moving the lights higher up?

Whether or not the bitterness will be retained in the regrowth after cutting the lettuce back, I'm not sure. However, I can tell you that while high heat levels will affect the bitterness of lettuce, for the most part the bolting phase of lettuce is controlled by the accumulated amount of light your plants have received. Beginning in the 1930s, researchers in the California university system tested a variety of lettuce cultivars and determined that light accumulation, not heat, was most significant for inducing bolting (they grew cultivars in heat ranging from 70F-95F, and these temps had less effect on bolting than how long the crops grew/received light).

Using fans for indoor growing is generally a good idea - it helps to circulate stagnant air which both prevents mold/fungi growth and provides leaves with greater contact with carbon dioxide.

I am personally torn (not crying myself to sleep, but I am puzzled) on the question of whether bitterness in greens dissipates after cutting and regrowth.

What kind of nutrients are you using? Chemical or organic? Sometimes chemical nutrients give lettuce a bitter taste because it is ment to be harvested in 5 weeks but you may have left it for 6 or 7?

I'm using chemical nutrients. I changed the lights from a metal halide lamp to 4' fluorescent bulbs as they don't give off heat like he mhl's do. They seem happier but I haven't tasted them yet. I did take one of the lettuce heads and put it outside over night in the rain, (it was 40F that night) and that one definitely lost any trace of bitterness. So I guess if I just wash/soak the lettuce in super cold water it should eliminate the bitterness. I wasn't aware there were organic nutrients, I think I will look into that for next time. This is my first time with *any* hydroponic system so definitely a learning experience.
Thank you :)