In the last article I explained what a surface area to volume ratio is. For this article I'll write about why it concerns coffee and tea. Remember, that the smaller SA/V an object has the more rapidly the object will react with its environment. Perhaps the most important reaction that coffee and tea undergoes is brewing! Because a an increasing SA/V, the finer coffee is ground, the more rapidly it will brew. As a very generalized rule of thumb, the compounds in coffee and tea extract in such a way so that the good stuff comes out first and the more unpleasant tasting compounds come out later (thus overextraction of coffee or tea is something that needs to be avoided (underextractoin is also to be avoided)). This is why when coffee is ground coarsely (such as for a French press), the grounds and water need to be in contact for 3-6 minutes for optimum extraction, and when it is ground very fine (such as for espresso), the grounds and water need to be in contact for just about a second for optimum extraction. So the lower the SA/V of the coffee grounds, the longer one needs to make the brewing time to achieve optimum extraction.

   The same issues being true for tea - tea dust and fannings extract very quickly, thus pretty much always overextract, so to get a cup of tea that is not overextracted one needs to turn to broken or whole leaf grade tea (loose tea). So that the extraction happens slow enough that the tea may be removed before the extraction progresses to far. SA/V is also the reason coffee should be stored as whole beans as opposed to grounds. Coffee goes stale through the process of oxidation and the higher SA/V the coffee has, the quicker it will go stale. This is why whole coffee beans will be good for about ten days, but if they are ground to a fineness used for espresso, they will be good for less than a minute.