Lemon turned broccoli purple I cooked broccoli with lemon and it turned purple/brown. It’s been a while but I believe I was steaming broccoli and added lemon to the water. It tasted bad—not like broccoli or lemon. What happened?

Any general rules about cooking vegetables with lemon? Is it always added at the end of the cooking process?
Normally, acids will turn broccoli a dull grayish color, and I don't recommend adding the lemon juice until right before you serve. For one thing the lemon juice will lose its flavor when cooked. 

Acids affect many, many foods when cooked — some for good and some for bad, so you do need to be careful when you add it. For example, acids added to beans before cooking will toughen them quite a bit. Acids added to proteins will denature them. And we all know what happened to Timothy Leary.