This post is quite off topic for what I normally post, but it caught my interest recently.
Foam that collects on the surface of tea, sometimes.
The reason it interests me is because it only happens with some teas, and only some of the time; hot, iced, black, green...etc.
I was brewing a Kenyan CTC tea the other day, and when I poured it, foam collected.
When I brewed a full leaf Assam, there was no foam.
I poured a green tea into two different cups; one had foam, and one did not.
Now, the picture (disclaimer) I did not take. The picture is also of instant (powdered) iced tea. I already know the reason that instant tea foams; the amount of solubles, like sweeteners, as well as the mixing process that introduced oxygen into the mix.
But why does loose leaf tea occasionally collect foam?
Search Google and a variety of answers (sometimes incredibly comical) will appear.
Some of the reasons I found:
-Soap residue from a dishwasher that couldn't perform its function properly.
-The introduction of oxygen into the water, when poured, stirs up tannic acid and causes it to foam.
-The mixing of hot and cold water makes foam.
-The dissolved solids in the water cause the foam.
-Hot water scalds the tea and creates the foam.
-A chemical reaction between sugar and caffeine.
-Extremely fine dust and foreign particles on the leaves float to the surface and collect as foam.
-Microwaved water makes tea foam.
-The foam is denatured proteins that detach from the leaves when hot water is poured onto them.
I do not know if any of these are the correct answer, but it was entertaining reading and looking some of this information up! If anyone else digs up anything, please feel free to share!