Coffee foam vs. Tea foam
One sign of really good fresh well-roasted coffee beans is foam. When you pour hot water into the French press, it foams, often forming a head up to 2" high. And when you use an espresso machine, you get a nice foam called "crema".
However, if you pour hot water into a teapot and see foam, that's a sign of terrible tea and you should throw it out.
Questions: what chemical reaction is taking place in each of the two cases (coffee and tea), and why does coffee get less foamy when it gets older whereas old tea gets more foamy?
Best Answer
During roasting, carbon dioxide is generated (the beans are burning, after all) and trapped in coffee beans. According to the book Espresso Coffee, a kilogram of freshly roasted beans contains as much as 10 liters of carbon dioxide. This carbon dioxide is the main gas component of espresso foam. Over time, unused beans will release that gas into the air, or de-gas, leaving less to create the crema on your espresso.
They say that coffee is not best immediately after roasting, but needs a few days to reach its peak. I've heard that this is because of the excess carbon dioxide, and I've heard that the "flavors need to develop." I'm not sure what the truth is. I don't normally get my beans that soon after their roasting, so I can't speak personally to the differences.
I don't know much about tea, so I can't help you there...
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What is the difference between froth and foam?
They are basically the same thing in regular usage. The milk in my coffee is frothy. The coffee has froth on the top. The milk in my coffee is foamy.What is the foam on coffee called?
Coffee beverage known as espresso, must be topped by a velvety thick, reddish-brown foam called crema, to be considered properly prepared and to be appreciated by connoisseurs.What is the foam on cappuccino called?
Microfoam (top) is used to make a wet cappuccino, whilst milk frothed with larger bubbles, called macrofoam (bottom), is used for a dry cappuccino.What causes frothy tea?
There's nothing to worry about when you see the foam appear. When hot water comes in contact with tea, it extracts the amino acids and proteins that result in such foam. The reason that you get more foam on the surface is when you microwave the water is perhaps dip the bag in hot water.How To Make Cappuccino At Home (with French Press)
More answers regarding coffee foam vs. Tea foam
Answer 2
A partial answer to start...
Crema isn't just foamy coffee. When you make espresso, hot water is forced through the grounds at high pressure, which extracts normally insoluble oils from the grounds and creates an emulsion of oil droplets and strong coffee.
Offhand, I can't find anything that explains why older beans don't produce as good a crema as fresh, it seems to be one of those things that "everyone knows."
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