I checked Google and found a bunch of info on growing lettuce that’s not bitter, but how do I make sure it won’t be bitter when I buy it from the store (iceberg particularly)?
Are big heads better than small ones?
Green Vs yellow?
Light Vs heavy?
Help me out here – what do I look for at the store to avoid bitter lettuce?
All greens have a tinge of bitterness to them, some varieties more than others. That said, I’ve never had any iceberg lettuce where there was enough flavor of any kind to detect said bitterness. If you taste that, then you must have super-sensitive bitterness receptors.
Give butter lettuce (also called Boston lettuce) a try. You might like that better.
When using iceberg, I’ve always found the bitterness to be concentrated at the bottom of the head. I avoid pieces that are thick and white.
Lately I’ve switched over to green leaf lettuce, as we prefer the texture and flavor and it seems to keep better / longer.
Generally speaking, plants make more bitter alkaloids the older they are and the larger they grow. This is why young dandelion shoots are tasty, but large leaves are icky. Lettuce, being a mutant dandelion cousin, is much the same way. Look for small heads (without evidence of outer leaves being torn off by wicked grocers) which are heavy for their size and you should be safe.
It seems like I’ve been getting a lot of bitter shredded lettuce in sandwiches lately from places like Jimmy John’s. It isn’t a pleasant bitterness like you get with a nice mixed green salad - it’s this gross chemically taste. Ugh.
IME, that’s more likely to be herbicide, pesticides or preservatives than the naturally occuring (herbicidal, pesticidal, preservative) bitter compounds in the plant itself. Ick. Tell your manager his staff needs to wash the lettuce more thoroughly.
Small heads of lettuce are less bitter, because they’re younger. (IOW, what WhyNot said).
Heavier heads of lettuce are better because the heaviness shows that they contain more water, which means they’re fresher.
However, I too have never noticed any bitterness in Iceberg lettuce, so either you are more sensitive to the receptors for bitterness (like Claire said) - this sensitivity does vary among individuals and changes with age - or you need to try organic lettuce and make sure it’s washed really well.
could you sneak a taste in the store?
I actually like the bitterness, and I find it in the lighter-colored leaves toward the center and bottom of the head. Sometimes I’ll even throw out the very green leaves on the outer layers. If you lived near me, I’d be happy to split the lettuce head with you 
OK - buy small heavy heads and send the white nasty stuff to Hyperelastic 
Got it - thanks!