A really simple recipe for a batch brew, is 55g – 60g per litre. The larger the batch (for example, 4L) you would brew a better cup brewing 55g per litre as with the large brewers, a 4% bypass actually creates a sweeter cup of coffee.
At Modern Standard Coffee, we are fans of the Bunn brewers, and many of our customers have the ICBA or CWA models brewing up our coffee.
For the ICBA, we recommend 55g per litre with a 4% bypass, using the easy pulse option.
The grounds begin to absorb the hot water from the sprayhead and release gasses from the coffee. For consistent extraction from all parts of the coffee grounds, the entire bed of coffee must be evenly wet in the first 10% of the brew cycle time.
The water-soluble materials dissolve and move out of the coffee grounds and into the water. The best flavours are extracted at the beginning of the process as seen in the Brew Cycle Time table.
Through this chemical reaction, the materials created during extraction break down further into water soluble proteins and sugars.
The brewing or water contact time with the coffee grounds is primarily determined by the grind size and bed depth. A longer brew time is required for the water to penetrate the larger grind particles. The recommended brewing contact times for each grind size are shown here.
Brewer Cycle Timing
The brew cycle delivery time of a coffee brewer assists in determining the recommended coffee grind to produce a quality cup. Experimenting with a coarser or finer grind will help operators discover the preferred coffee flavour profile.
The ideal depth of the coffee bed in the brew basket is 2.5 – 5.0 cm regardless of the volume of brew. If a coffee bed is less than 2.5 cm, the water may move through it too quickly and under-extract. Water moving too slowly through a bed depth of more than 5.0 cm may cause over-extraction and a bitter taste.
According to this chart developed through years of research and testing and now used by the Specialty Coffee Association, every great cup of coffee has three important variables—strength, extraction and brewing ratio. By plotting the relationship between these factors, it is possible to produce the ideal coffee flavour and drinking experience.
By using the weight of ground coffee in the brew basket, the volume of water used, and the strength of the brewed coffee, you can plot these to determine the extraction. The objective is to get to the Optimum Balance area. If you use 55g of coffee and the strength of the brew was determined to be 1.50%, follow the red line labeled 55g down the red diagonal to the 1.50% grid line, and then straight down vertically to the bottom of the chart to extraction which is approximately 23.5%. This coffee is STRONG / BITTER. To move the brew outcome, the extraction needs to decrease and fall within 18% – 22% by decreasing the brew time and/or increasing the grind size.
The red diagonal lines represent brewing ratios of ground coffee used per half-gallon of water. The ground coffee measurements are displayed in ounces across the top and down the right side of the Chart.
The left side of the Chart indicates strength as a percentage. Other Control Charts may include total dissolved solids (TDS). The ideal percentage of coffee flavouring material in the finished cup is 1.15% to 1.35%, and is most accurately measured by a Brew Strength Meter, hydrometer or refractometer.
Approximately one-fourth to one-third of a roasted coffee bean is matter that will readily dissolve in water during the brewing process. The other portion is bean fibre that isn’t soluble during normal brewing.
The bottom of the Chart converts the fraction of the original dry ground coffee that has ended up in the finished cup to a percentage. The ideal range is 18% to 22% of the solubles. Grind size and brew time play a critical part in extraction.
Balancing strength and extraction produces a standard designated as “Golden Cup” by the Specialty Coffee Association of America.