Pulse Brew and Pre-infusion: New Tools for
Filter Drip Brewing.
There will always be more questions than answers when discussing any subject,
and coffee brewing is no exception. Everyone you talk to has an opinion about
how a properly brewed cup is prepared. Differences in the brew caused by the
method used in the separation of the grounds and finished beverage can alter
your taste experience as well as the strength and extraction analysis.
These variations alone create debate as to which delivers the perfect cup
experience. Since the 1960s, the most accepted method of separation has been
paper filtration for filter-drip coffee. I would venture to say the majority of
today's coffee drinkers in the United States haven't tasted coffee that has been
brewed by any other method.
Many methods, but only two standards
Throughout my time spent learning about coffee brewing (something I hope never
ends), there have been only two recognized sets of standards to determine a
properly brewed cup of filter coffee. The majority of this work was done in the
1950s through the early 1970s. These standards set a recipe or formula for water
to coffee ratio that can deliver a balance of strength and extraction and are
achieved through a brewing method that combines time and temperature. All of
which have recognized tolerances. With all the advances in the world of coffee
technology, it's time to take a fresh look at how a properly brewed cup is
determined.
First let's look at existing brewing standards. These standards were developed
by the Coffee Brewing Institute Inc. (CBI) an affiliate of both the National
Coffee Association and the Pan American Coffee Bureau. When the CBI was formed
in 1952, it marked the first time a scientific study of coffee beverage was
conducted in the United States.
In 1964, the now-defunct Coffee Brewing Institute was replaced with the Coffee
Brewing Center (CBC). The CBC focused its work in the foodservice sector,
promoting the brewing standards created by the CBI. The CBC developed the
original Golden Cup Award program to promote proper brewing techniques at the
restaurant level and to provide training to the foodservice trade. The CBC
closed in 1975.
Meanwhile, across the Atlantic, the European Coffee Brewing Association was
established in 1971 by the Norwegian Coffee Association. The association's
mission has been to improve the technical qualities of the brewing equipment,
and to inform, train and educate professional and consumers to properly brew
their coffee. Thankfully these concepts are back in the mainstream conscience of
today's roasters, manufactures and consumers. The Speciality Coffee Association
of Europe (SCAE) and the Specialty Coffee Association of America (SCAA) have
programs promoting quality brewing. The SCAE Gold Cup program and the SCAA
Golden Cup programs are designed to provide education to all involved in the
coffee trade.
Part 2: Pulse Brew and Pre-infusion
The Crucial Three: Time, Temperature, Water Quality
The three most important variables required to extract the desirable materials
from the ground coffee are time, temperature and water quality. The time water
is in contact with the coffee is the controlling factor to remove the amount of
extraction desired. The smaller the grind sizes the shorter the time required
for a brew cycle. The grind size and bed depth of the ground coffee are the
factors that determine water contact time. Recognized times are listed in the
chart below. These times apply regardless of the volume brewed.
GRIND TIME
Water contact with the coffee grounds
Fine 1-4 minutes
Filter 4-6 minutes
Coarse 6-8 minutes
Beverages are analyzed for soluble concentration (strength) to determine the
percentage of the beverage that was the soluble material from coffee. The most
enjoyable beverages had 1.20-1.45 % of coffee soluble material.
Extraction (yield) from the grounds was also analyzed. Extraction of less than
18 % of the brewing material was determined to be underdeveloped and coffee was
wasted due to under-extraction. If a coffee was more than 22 %, undesirable
bitter flavors were removed. The desirable extraction limits were determined to
be within a range of 18- 22 % of the original weight used in the brew.
The grind designations of fine, filter, and coarse each have specifications and
allowable tolerances.
The water temperature required to efficiently extract the desired soluble
materials and aromatics from the ground coffee should be delivered within a
range of 92C - 96C throughout the brew cycle.
Water quality is critical to the perfect brew. Ideal water is good-tasting,
odorless and has no visible impurities. A total concentration of dissolved
minerals in water below 300 mg/l should deliver a quality brew. A pH measurement
of 7.0 or neutral is desired. A range of +/- 1.0 is acceptable.
Better beans, better brewers
In the past five years, I've seen great improvements in the quality of specialty
grade beans as well as dramatic changes in coffee roasting technology. Brewing
technology has also made great strides in temperature consistency and delivery
systems of the water as well as filtration and funnel basket design. Today's
equipment far surpasses what we previously had available for brewing coffee.
The majority of lower volume brewers (two liters or less) may have the least
amount of adjustment available to the end user. Although most have a precise
temperature and volume controller, only those introduced recently offer control
over delivery time for the water. The latest technologies of pulse brew and
pre-infusion provide the roaster or end user the option of controlling the water
cycle time, which affects the total brew cycle time.
You may ask yourself, why do I need this feature? One answer is that these
features allow you to control the water cycle time and use a different grind
size. Now you can choose a coarser grind and program the brewing equipment to
accommodate with a longer water cycle time. These features can provide a new
experience in the cup to enjoy.
As brew water comes in contact with ground coffee, the first wetting phase of
the brew cycle begins. At this point in the brewing process, the coffee grounds
begin to absorb the water into the cell structure of the broken bean. This
prepares the grounds for the extraction phase by saturating the inner and outer
surfaces of the coffee cells.
Pre-infusion gives you control over the initial volume of brew water dispensed
over the ground coffee. This feature dispenses the amount of brew water
specified over the grounds, pauses so that the cell surfaces have a chance to be
saturated, then dispenses the remainder of the brew water. A simple analogy
would be a comparison of the pre-soak cycle for laundry. The goals are the same:
to remove the material that is bound up in the fabric/cells of the material by
controlling the initial volume to completely saturate the material, allowing
time for absorption, then continuing the remainder of the cycle.
A multitude of factors can affect coffee brewing: terrain, climate, processing,
or roasting, to name a few. Experimenting with pre-infusion can open up a whole
new flavor profile in the cup. I have found that very fresh-roasted and ground
coffees respond well to pre-infusion. The initial phase of brew water assists in
the release of the carbon dioxide gasses in the coffee cell structure. Followed
by the adjustable pause, the cells have time to release some of the gasses and
allow water to more easily penetrate the inner cell structure during the
remaining water cycle.
Pulse brew is another method for extending the water contact time with the
ground coffee. Pulse brew routines consist of an initial on time followed by a
series of off-and-on periods that dispense brew water over the grounds.
Pulse brew assists in flavor-matching coffees brewed in a multi-volume brewer.
Ideally a brew funnel is sized to one volume. Today, customers look for
flexibility in the equipment, brewing larger quantities at peak demand and
smaller quantities during slower periods to reduce waste. As a result, they brew
fresh coffee more often. Brew funnels are generally sized to accommodate the
larger brew volumes. When the smaller weight/volumes are placed in the funnels
the bed-depth of the grounds is too shallow for good brewing. Without the
advantage of programming a pulse brew routine to elongate the water contact with
the grounds, the quality of the beverage suffers.
Without experimentation there is no innovation. Learning to use the tools
provided by the equipment manufacturers will enhance your coffee program.
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