Or, how to diagnose espresso extraction problems.
The Italian four M's (barista, grinder, blend, and espresso machine in English) encompass the key elements of producing exceptional espresso. It's tempting to focus on the last one; indeed, one of the most frequently asked questions on Home-Barista.com's forums is a variant of "What espresso machine should I buy?" Once a shopper narrows their list to a few choices, one of the issues experienced home baristas regularly debate is the techniques and merits of obtaining ideal brew temperature. The previous how-to, How I Stopped Worrying and Learned to Love HXs, was my contribution to the finer points of brew temperature management.
Despite the importance of the espresso machine to the final result— in fact the search for equipment reviews is what brings most readers to this site —I argue the other three elements are equally if not more important. At the top of my list is the contribution of the barista, and not only in the careful choices that bring these elements, but also the skills the barista needs to master. How well the barista has developed these skills is first revealed while watching the less than half-minute extraction that produces an espresso and ultimately in the cup.
Appreciation of the importance of the extraction to exceptional espresso reached a new level of clarity last year with the introduction of "bottomless portafilters" by members of the Barista Guild (the modified portafilter is also referred to as a "naked portafilter" or "crotchless portafilter"). Inspired by Chris Tacy's diagnosis series Training with the Naked Portafilter, I started my own case study.
Join me in a revealing look at what's happening beneath the business end of an espresso machine's portafilter! Our journey starts with a brief review before jumping into the diagnosis hints and tips for espresso extractions gone awry.
A smart barista will intently watch the stream of espresso pour out during an extraction. While appearance alone isn't definitive proof of a good cup, it does go a long way in verifying the barista's technique. Describing what the barista is looking for requires we first review a few terms, some of which are excerpted with permission from the Espresso Glossary by Mark Prince:
Blonding denotes the color transition of a pour from dark brown and tiger-striping to a light, uniform pale blond. This normally occurs in the last third of the pull and is a signal to end the pour. This overly-blond portion of an espresso is thin, nearly flavorless, and if allowed to continue too long, will dilute the body and taste characteristics of an otherwise enjoyable shot.
Channeling is the rapid passage of water through fractures in the coffee puck, which produces a thinner, under-extracted espresso. When it occurs, you'll often see sudden appearances of blond streaks in the stream of espresso; sometimes the puck will even have pencil lead-sized holes where channeling occurred.
Crema is one of the sure signs of a properly brewed shot of espresso (in non crema-enhancing espresso machines) and is created by the dispersion of gases— air and carbon dioxide —in liquid at a high pressure. The liquid contains emulsified oils, and forms a dark golden brown layer resembling foam on top of an espresso shot. [excerpted M.P.]
Extraction is the act of forcing hot water from the boiler though ground coffee, which in turn "extracts" flavors, oils, colloids, lipids and other elements that turn water into brewed coffee or espresso. [excerpted M.P.]
Golden rule is a common phrase that describes the ideal extraction time and volume for an espresso. The Instituto Nationale Espresso Italiano (PDF) provides a working definition of the characteristics of an ideal espresso, although I consider these parameters more "golden guidelines" than hard and fast rules. My own brief definition of an espresso is an extraction using approximately fourteen grams of coffee to produce a sixty milliliter double in 22 to 32 seconds (timing from the moment the pump starts).
Over-extraction occurs when too many coffee solids are extracted, resulting in a strong, harsh flavor. The visual signs are a low-volume extraction having a dark, thin crema. A dark "halo" at the edge of the cup is another classic indictor of an over-extraction, or of brew water that is too hot.
Pre-infusion: the act of pre-wetting the bed of ground coffee inside an espresso machine before actually commencing the brew. Some espresso machines do this by using the pump; water is pumped to the coffee for a second or two, and then halted for another second or two. After this pause, the pump activates again, and continues brewing the shot. Super automatics and some automatic espresso machines use this pre-infusion.
Another type of pre-infusion is called "natural" or progressive pre-infusion, and occurs in espresso machines equipped with an E61 grouphead. When the pump is activated, a secondary chamber must fill prior to full pressure being applied to the bed of coffee. This gives a 3 to 7 second saturation time for the grounds before the pressure builds up. This type of pre-infusion is preferable to pump and pause active pre-infusion.
There is a school of thought that progressive pre-infusion improves overall extraction from the coffee. [excerpted M.P.]
Tiger striping and mottling are leading visual indicators of a good extraction. Tiger striping is formed by the contrast of darker and lighter crema in the espresso stream; ideally it begins early in the pour and is sustained through the end. Mottling is the in-cup confirmation of a good extraction; it is the darker brown speckling and reddish-brown splotches formed on the surface of the crema.
Under-extraction occurs when too few coffee solids are extracted, resulting in a weak, dull flavor. The visual signs are a rapid, high-volume extraction having a uniformly light blond crema.
Terminology out of the way, we can now turn to how to recognize a proper extraction—and the bottomless portafilter can certainly make it obvious! To the right is an example extraction from a Cimbali Junior DT1 that shows excellent tiger striping. The coloring is evenly distributed and was consistent throughout the pour.
As mentioned in the mini-glossary above, the "golden rule" of an ideal espresso specifies an extraction timing and volume. They are good guidelines, but the coloring is in many ways a better indicator of the correctness of the grind and tamp.
Watching the extraction using a bottomless portafilter dramatically shows how the extraction is progressing, however one isn't absolutely required. Careful attention to the stream exiting the pour spout of a "normal" portafilter will show many of the same signs. Coloring will give you a clear idea when is the correct cutoff time, keeping in mind that tiger striping fades as the beans age. Also note that decaffeinated coffee stripes very little; it generally starts out darker and more uniform than the caffeinated equivalent and turns blond earlier. Of course, freshly roasted beans have more color striation during the pour too. Depending on the blend, four to ten days post-roast will give you the best results.
Although stopping the extraction when blonding ensues will generally get you the best shot possible for a particular extraction, correcting for an improper rate of extraction leads to the road of better espresso. If the extraction is too slow, the espresso may be bitter with a dark brown crema; if the extraction is too fast, the espresso tends to be sour and the crema uniformly cinnamon colored. Taste is your ultimate guide to correcting errors in grind, dosing, and temperature. Applied consistently, getting good shots is mostly a matter of technique.