you are enjoying your vacation Dr. Brew! This is Part 2 of an article entitled Pulse
Brew and Pre-infusion: New Tools for Filter Drip Brewing originally published in the Q1 2008
issue of Tea Coffee Asia.
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.
Water contact with the coffee grounds
Fine 1-4 minutes
Filter 4-6 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
The water temperature required to efficiently
extract the desired soluble materials and aromatics from the ground coffee should be delivered within a
range of 92° C - 96° C 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.
beans, better brewers
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.
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
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.