Even very experienced baristas often don't take advantage of the
opportunities to improve the espresso that are available while making
the shot. They lock the portafilter into group, turn on the pump or pull
the lever, and pray. If the shot is roughly right, they'll serve it and
make small grinder adjustments for the next one—if it's way off,
they'll dump it and make larger grinder adjustments. This approach
requires that grind settings and machine temperatures and pressures be
very close to perfect. However, if you know a few things about how
espresso extracts, you can correct somewhat larger deviations from the
correct levels of these variables on the fly. Moreover, however correct
or incorrect the variables, you can assure that you're getting the best
espresso possible under the circumstances.
Ending the Extraction by Color
The first aspect of working the shot is to make sure the extraction
is correct by ending the shot at the same color every time. The exact
color depends on blend and machine, but it is always a light tan
described by experienced baristas as blonde. If the stream is still well
filled with crema, it is not yet blonde. If the stream entering the cup
discolors the crema into a light tan color, it's gotten lighter than
blonde. Typically the right point is around the time when the stream
starts changing from foam to liquid.
How and why does this work? Underextracted coffee is sour and thin;
overextracted coffee is weak, with bitter and acrid notes. As the ground
coffee extracts, the water flowing through it colors less and less. So
the color is a measure of the degree of extraction and stopping at the
same color means stopping at the same level of extraction. Perfect
extraction occurs when 20% of the ground coffee's weight has dissolved
into the coffee. Knowing the color that corresponds to this so you can
stop the extraction means getting the best espresso for a given pull
The graphic below illustrates the 'extraction space' of espresso,
showing shot time and volume, the changes in color, and the effect of
grind fineness. It will be used extensively in the diagnostic section,
but will also help clarify the concepts discussed here.
Let's suppose the grind is way off and you don't know about this.
Based on what you've read, you are looking for a two ounce double
espresso in 27 seconds. If the grind is too coarse, you get the two
ounces in about 15 seconds. If you stop there, the cup will taste
underextracted. If you go for 27 seconds, you'll get an overflow of
overextracted bilge. But if you stop the shot at the right color, you'll
have a 20 second, 3 ounce lungo (long shot)—not what you wanted,
but quite drinkable. Now suppose your grind is way too fine. If you
don't know the rule, you'll have a ½ ounce of intensely sour
stuff at 27 seconds, or 2 ounces of intensely bitter stuff after a
minute. If you do know the rule, you'll have a 1 ounce ristretto (short
shot) after 35 seconds—again, not what you wanted, but enjoyable
nevertheless. After you tried the shot, you can correct the grind, or
even stay with the "mistake" if you decide you liked it more. In any
case, you'll have a range of shot possibilities you can explore.
As can be seen on the extraction chart, it takes a longer time for
the flow to go blond on a restricted volume shot than on a long volume
shot. This relation between shot blonding and the volume and length of
extraction is known among espresso enthusiasts as Al's Rule,
named after Al Critzer of Cimballi.
Taking Advantage of the 'Rule of Thirds'
Sometimes it is not the grind, but the temperature, pressure, or even
the blend itself that are off. Ideally, you would fix this by correcting
the problem directly (see next section), but in many cases it takes more
time that you have before rushing off to work, running errands, and so
on. Another aspect of the extraction allows for a quicker fix. The early
part of the extraction contains a predominance of the acids and the
portion derived from fines. The central part of the extraction contains
a predominance of the sugars and caramels. The final part of the
extraction tends towards bitterness, but will also be fairly weak,
sometimes almost tasteless. Among enthusiasts, this is known as the rule
So, if the espresso is too sour, or worse, has the citrus peel
acridity from high grown fines (a bright lingering bitterness mainly on
the roof of the mouth), let the first second or two of the flow go into
the drip tray. This is an old Italian barista trick for dealing with
rioy Brasils, but it can also be used on gourmet blends containing a lot
of acidy high grown coffees.
On the other hand, if the espresso tastes flat or bitter-dull, stop
the extraction at a darker color to reduce the proportion of weak
bitterish coffee, and increase the proportion of the intense flavors
from early in the shot.
If the espresso is not sweet enough, you can do both by capturing the
flow after a few seconds and ending while the flow is still darker. This
"center-cut" shot will favor the sugars and caramels in the extraction.
Next page: Better extraction, better espresso...