Coffee Engineering

French press coffee is a thick, full-bodied brew. At brew-time, coffee and water are separated by the semi-porous plunger screen, allowing some fines to mix with the finished product. The presence of these fines is polarizing because of their influence on mouth-feel, however they're an undeniably part of the French press experience. Within the French press beaker, coffee is exposed to water for a lengthy period in comparison to other methods. This extended coffee-water interface is counterbalanced by a very coarse grind size which yields a full-bodied cup, while ideally avoiding over-extraction.

The French press hardware is simple, inexpensive, and requires no consumables (i.e. paper filters or other non-reusable components). Cleanup is trivial if one has access to a garbage disposal; those less fortunate must devise more creative disposal methods. 

The full manifest of materiel:

I find light roasts reveal the most flavor and character of the bean. Medium to dark roasts induce too much bitter, burny angriness for my tastes. In Chicago, my favorite roasters are Intelligentsia and Bow Truss.

Roasted beans should be ground in a high quality burr grinder immediately before brewing. Bladed grinders, while cheaper, do not afford an adequate degree of accuracy or precision over the fineness of the resulting grind. 

The grind affects the overall surface area of the coffee that can be exposed to water, with surface area varying inversely with grind size. That is, the finer the grind, the greater the surface area. Ultimately, the finder the grind, the more extracted the finished product will be. For French press brewing, a rather coarse grind is desirable for two reasons:

1. The grounds are exposed to water for a relatively lengthy duration, so a fine grind will lead to an over-extracted finished product.
2. A fine grind will clog the press's plunger screen which can make operating the press difficult or even dangerous.

The ratio refers to the rate at which coffee and water are combined in the brew, by weight. Obviously, increasing coffee at the expense of water will lead to a stronger brew. 

My preferred ratio of coffee to water is 3:50.  This means that for every 1,000 g  of water, one adds 60 g of coffee). The only way to get such an accurate measurement is using a food scale. Fortunately, using a food scale is highly convenient, as coffee and water can be measured directly into the beaker. No dirty measuring cups or spoons.

The temperature of water as it is mixed with the grounds in the breaker has an effect on the degree to which the grounds extract into the water, with extractedness varying directly with temperature. 

Controlling temperature requires the use of a thermometer. I use a Taylor Classic Instant-Read Thermometer, which fits conveniently right in the whistle-hole of my kettle (oh my). Even using a thermometer, achieving the desired temperature can be a tricky process. Unless you're lucky enough to own a variable temperature electric kettle, water must be boiled and then allowed to cool to the desired brew temperature. 

I find 200-205°F to be a temperature range that produces a desirable degree of extraction. 

Like temperature, the time the coffee-water mixture is allowed to brew affects the degree to which the grounds extract into the water, with extractedness varying directly with brew time.

I find four minutes to be an adequate amount of time to allow the coffee to impart flavor without over-extraction occurring.

1. Measure n grams of beans. Grind coarsely and deposit into the beaker.
2. Heat the water to the desired temperature. With the beaker on a tared scale, start the timer and slowly pour in m grams of water, where m = 50 * n / 3
3. With a wooden spoon, break up the foamy crust that forms on the coffee. The goal is to make sure that the coffee is submerged in the water and not floating at the top of the beaker. Vigorous stirring is not the goal. A metal spoon may be used if shattering the beaker is not a concern (as with metal beakers). 
4. Place a plate over the top of the beaker to prevent heat-loss.
5. Once the brew timer has expired, remove the plate. With the wooden spoon, remove and discard as much of the coffee crust that has resurfaced as is reasonably possible.
6. Insert the plunger. Press on the plunger knob slowly and steadily. 
7. Immediately pour off the coffee into a heated mug or carafe. Allowing the coffee to remain on the grounds will increase extraction.
8. Enjoy.

Using the previously described methods, one can iteratively refine their coffee until it reaches one's own manifestation of perfection. Through careful variable isolation and observation, one's coffee can be made repeatably excellent. 

In the same way that crafting great coffee is like crafting great software, I suspect those who love to craft coffee are like those who love to craft software. While many people can appreciate a finely crafted cup, it takes a unique personality to want to learn the procedural intricacies of how that cup was made. So it is with software engineering.