Grinding And Selecting Your Grind
The grind size we recommend is:
Fine: This grind is ideal for Bialetti Italian stovetop coffee makers. However, for a real, manual espresso machine we recommend having your own grinder; even a small, manual handgrinder will work.
Medium: Drip filters such as a Hario V60 or a Hario Woodneck as well as your common automatic drip filter machine.
Coarse: French Press
The correct grind has a very large impact on the final coffee beverage. It can play the difference between uninteresting and bland coffee, over-extracted and bitter coffee and the perfectly smooth cup. The reason there are different grinds is because different coffee preparation methods put the coffee grinds longer in contact with the hot water. Basically, the longer the coffee grinds are in contact with water, the coarser the coffee should be ground. This is because the finer it is ground, the more surface is in touch with the water and the quicker the extraction processes.
For example, if you take a French Press and add coffee and hot water, the coffee steeps in the water for three to five minutes before the plunger should be pressed down. Making an espresso on the other hand puts the water into contact with the coffee for just 25 seconds or so. Imagine an espresso grind in a French Press. You can do an experiment at home and try this out to see the result. Or better yet, just take our word for it as besides clogging up the French Press, the coffee will taste bitter and over-extracted. On the other hand, putting a coarse ground coffee in an espresso portafilter will produce something not much better tasting than dirty water!
So what happens when you overextract coffee? Basically you get a lot of bitter components (which you don't want) in addition to the nice fruity acidity and sugars (that you definitely want). Caffeine is extracted at the beginning so even a short brew time will not affect caffeine content.
Water temperature also affects the extraction process, but to a lesser degree. With the water temperature the issue is more WHICH solubles are extracted rather than HOW MANY (but going into detail here quickly becomes a bit scientific and nerdy). We recommend brewing coffee at 93 degrees Celsius as this is the generally accepted balanced temperature for optimal coffee extraction.
If you want stronger coffee, it is always better to just use more coffee rather than brewing it longer. This results in more coffee solubles being dissolved in the water without extracting the bad, bitter stuff mentioned above.