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Given the following post, respond as if you're commenting on Reddit:
human
When one washes the dishes, is the soap foam a good 'practical' indicator about how dirty is the water?

When I wash the dishes at the start the sink is full of hot water with a bit of soap, and a lot of foam is generated while the sink is filling. 

Then I wash the dishes starting from the less dirty to the most dirty, and until the end the water is more or less clear with a lot of foam. As soon as I start to wash the dirty dishes the foam diminishes a lot and the water gets darker. 

I remember that soaps reacts mostly with fat, so I was thinking that the level of foam is a good indicator of how much 'not bound'/' not used' soap is remaining. Is that so? 

Thanks for the answers, in the meanwhile I see if I can improve my results with search engines to refresh my little chemistry knowledge.
gpt
It is a good indicator about how much soap is left to clean off your dishes.


Soaps don't truly react with anything, but they do surround fats and oils and "pull it off" the dirty surfaces.  So if the soap is being used to surround a glob of oil, it can't make foam (which is basically air surrounded by soap).


Now the interesting part is that different soaps generate different amounts of foam.  In terms of cleaning ability they may be very similar, but not similar in foaming ability.  So most dish detergent contains stuff that makes a lot of foam so it looks very effective.


On the other hand, car wash soap contains (or should contain) less foaming agent because who wants to spend the time and water removing all that foam.