Homebrewing ala Chemex
Experimentation began by trying to discern the nature of extraction. I brewed a Chemex and separated the brewed coffee resulting from the preinfusion, 1st, 2nd and 3rd minutes. The order of extraction for flavors is well documented in espresso, and as I found, follows the same general principle in the chemex. Flavors come out in the following order: sour, sweet/creamy, bitter. Understanding that can give clues to how to make adjustments for an ideal extraction. Below are the parameters that I have considered and what I found that they influence.
The filter for the Chemex is part of what gives the coffee a smooth, silky mouthfeel. The intended filters are thicker than a regular coffee filter, the result is that nearly all suspended solids are filtered out giving a smooth clean mouthfeel and yielding a delicate cup. Titanium filters and cloth filters are also available that allow more grit through, changing the extraction and texture.
These two parameters are interrelated, and so can be discussed together. Both dose (amount of coffee used) and grind affect brew time and therefore the time of exposure for water to coffee as it flows through. The basic principle is that due to the increased surface area of finer grind, the time required to drain is longer, and thus a coarser grind will drain faster. Changing the dose will also affect the total extraction time, a larger dose will also increase the drain out time and a lower will subsequently decrease it. Play with this balance to achieve an ideal brew time (~ 3 minutes) as well as to understand how they change the flavor. You could try a fine grind, but lower the extraction time to 2 minutes, or a coarser grind and raise the extraction time. The same brew time with different grind/dose ratio will not yield the same cup of coffee!
Ideal extraction temperature is ~195-205º F, this will influence solubility of the flavor compounds, and will be very specific each time you brew. I like to just try to do the same temperature every time and keep it at ~200º F. Having a pouring device that maintains temperature well keeps this factor constant. Signs of under extracted coffee due to cool water would be watery, slick, lacking depth. Signs of over extracted coffee due to too high of a temperature would be burnt, toasty, lacking top notes.
I brew my Chemex by weight, on a kitchen scale. I add between 2 and 3 ounces of water carefully (for ~30 grams) to the dry grounds, just enough to wet them. This exposure releases gas trapped in the grounds and helps to open the pores of the grounds allowing for ideal extraction of the flavor compounds. The grounds puff up and "bloom." The size of the bloom will change depending on the freshness of your coffee, a coffee a couple days off roast would have a large bubbly bloom. We generally recommend aging coffee, usually 5-7 days off roast for optimal flavor.
My method is to pour right in the center of the grounds, and slowly spiral outwards. I also use the 'heartbeat method' when brewing a chemex; I add about 7 oz (~200g) water at a time, let it drain almost completely and then go for the next addition. Pouring gently can dramatically influence how your grounds settle and will affect the entire extraction. Whatever you choose to do, observe your process so its repeatable and link your process to your finished results. Could you explain it to someone so they could duplicate it? Take into consideration weight, time and color of grounds.
I like to stir, some people don't. Stirring adds energy, which increases extraction of the coffee at the point of contact. After understanding the nature of the extraction of flavors, stirring can be very interesting. A stir can bring out aspects of the coffee that are extracting as the stir is applied, i.e. an early stir could highlight bright, sour flavors. One note though, I have trouble stirring at home because it often causes the grounds to collect in the bottom of the filter due to my imperfect grinder. Depending on how you pour, this could also be adding agitation to the coffee.
When standing water is no longer visible, I pull the filter out. Give the coffee a quick swirl so it is properly mixed, and enjoy! A pre-warmed cup is always a great idea too.
My go to recipe for 1 large cup:
Coffee: 30 grams (I recently measured a level quarter cup of whole bean coffee to be ~22 grams, though this is variable)
Grind: Slightly coarser than for drip machines
Water: ~17 oz/500g @ 200 degrees
- Pre wet filter with excess water, allow to sit in the chemex to warm the glass before brewing, but don't forget to pour it out first!
- Add 30 grams ground coffee to Chemex
- Bloom/Preinfuse! Add 2-3 oz water slowly, completely covering grounds, wait until the bloom starts to settle (~20-30 seconds).
- Break bloom from center out, adding 6-7 oz hot water, if you want, stir immediately with a few very gentle stirs with a warmed spoon.
- When water level is almost below grounds, add the last 6-7 oz water and give another gentle stir.
- Pull the filter as the water level drops below the level of the grounds, give a quick swirl, taste!
- Brewing time should be between 3 and 4 minutes.
One of the best ways to increase consistency in brewing is to add water by weight instead of by volume. A good scale will also help by allowing you to measure coffee beans accurately, small changes in weight sometimes lead to huge changes in flavor!
A burr grinder will change your life! Compared to the blade grinders that are seemingly ubiquitous at home, it will give a much more precise grind size and will greatly improve coffee flavor and extraction. Hand grinders are great and portable, electric can be costly and large, but are easier and generally more consistent.
Knowing the right color to look for is a good way to help know if your parameters are good. Stirring can help develop good coloration, but it is also a result of perfect grind/dose to water ratio.
Try adjusting grind first, then fine tune with dose. Flavors associated with restriction are: syrupy, slick, dried, condensed flavors, burnt, deep, flavors seem far away. Flavors associated with a more open brew are: acidic, watery, juicy, refreshing, muted flavors, too close, toasty, brighter, lively. Try to find a nice balance, moving in the direction you need to balance your cup.
Chemex produces a very clean cup highlighting the delicate characteristics of the coffee, is not ideal for everyone, but most people find it incredibly delicious. If you want a more bold cup, then the thick filter might rob you of the sediment and oils you were expecting! These parameters can be more or less applied to any other coffee making technique!
Last important note, I think everybody should know that Wikipedia cites the Chemex as James Bond's preferred brew method for coffee, as seen in "From Russia with Love." So, if you want to brew like 007, try a Chemex.