geo (04/01/83)
Remember the discussion that was going on in this group a few months ago about tea bags, in which we speculated about why the bags became filled with air when one pours boiling water on them? The 'Amateur Scientist' in this months Scientific American is largely about the making of turkish coffee. Apparently, turkish coffee, when made properly, is covered by a thick foam "The foam is almost a side effect. The grains [of coffee] are so small that they provide plenty of surface area for adsorbing air. The tiny pockets of air are sites for the nucleation of bubbles. When the coffee and surrounding water get warm, air dissolved in the water comes out of solution at the nucleation sites, forming bubbles just barely large enough to be seen." This sounds like the same mechanism could be used to explain the tea bags filling with air when covered with boiling water to me. Thank you Jearl Walker.