If ever you still have yellow leaves on your bean plants, then the most likely cause is a disease. While there are other several causes, the most common are usually from blight or the mosaic virus.
If your green bean plant is under the attack of the mosaic virus, then it’s a serious problem. That’s because if it’s too late then you might not be able to save your plant. On another note, this happens when the plant is too weak to fight against the virus.
When I was researching we ran into the question “How do you get rid of yellow leaves on beans?”.
However, adding chelated iron or soil acidifier helps if the plants develop yellow leaves from alkaline soil. Beans have shallow roots, so exercise care when hoeing to prevent injuring the roots. Remove any old plant debris from the area as these may host disease organisms.
Nitrogen deficiency may cause plants and leaves to turn light green or yellow, as well as result in poor harvesting. The same goes for a manganese deficiency, which causes older leaves to yellow and produces dead brown spots.
Why do beans have air bubbles when boiled?
The foam happens because legumes are rich in saponines (see my longer answer here). It contains nothing more and nothing less than the water in which you boil the beans, it just happens to trap air bubbles because of its physical properties.
The next thing we wondered was; what happens when you boil beans in Step B?
Most of the time, and depending on the kind of bean used, the beans in the step B while boiling release lots of white foam. I usually skim the foam and throw it away as it takes too much space in the pot.
What is the purpose of the foam in a bean boil?
It contains nothing more and nothing less than the water in which you boil the beans, it just happens to trap air bubbles because of its physical properties. There are no specific culinary reasons for or against keeping the foam.
Another thing we wanted the answer to was; is it a waste to boil foam?
It is not much of a waste anyway, as a large volume of foam contains a very small amount of boiling-water-solution per weight. Thanks for contributing an answer to Seasoned Advice!