Several factors influence both the extraction percentage and the brew strength, but we will highlight three factors that have arguably the greatest impact on the outcome: 1.) sufficient understanding of the chosen brewing apparatus, 2.) proper brewing ratio, and 3.) proper grind setting.
It’s important to understand how a tool works in order to get the best performance out of it. When it comes to coffee brewing equipment, you want to be as familiar with how a device was designed to operate as possible. This includes answering questions like: Is it a machine that needs to be programmed or a device that is operated by hand? What size batches can it make? Is it a drip brewer or an immersion brewer? How long is the water in contact with the grounds? What kind of filter is used?
The coffee brewing ratio (CBR) is the ratio between the ground coffee by weight dosed into the brewer and the water by weight used for brewing. Given the many variables in coffee extraction, it is often useful at first to fix a brewing ratio that is known to be successful, and then practice and develop good results with all the other factors presented by your chosen device. Having done that, you can circle back and adjust the CBR later, if necessary. A useful starting point for CBR is a ratio of 1 part coffee for every 16-18 parts water, by weight. Using 6 g of coffee for every 100 g of water is an easy rule of thumb that falls in that window.
Using too much coffee can result in under-extraction due to the limited capacity of the amount of water to draw out all of the available coffee solubles that you have introduced into the system. Conversely, using too little coffee can lead to over-extraction as there is increased capacity on the water side to accept solubles.
Proper grind is essential. The correct grind depends on the device that you are using as well as the size of the batch that you intend to brew. Coarser grinds inhibit the water’s ability to extract solubles as they expose less overall surface area to the water. Finer grinds increase the ease of extraction by exposing more surface area. For brewing methods that have longer periods of contact time between the water and the coffee it’s useful to inhibit the extraction by using larger coffee particles. For brewing methods that have shorter contact time it is necessary to use smaller particles to encourage the extraction. Some devices, such as a standard batch brewer, allow for a range in batch size. When this is the case, it is important to realize that the amount of coffee in the bed of grounds also acts to inhibit the flow of water through the grounds. For smaller batches on the same device, use a relatively finer grind and correspondingly, for larger batches, use a coarser grind.
True, there are a number of other factors that impact the brewing process. But these three are undeniably significant, and form a great starting point for working to develop competency in brewing. Practicing with these three factors in mind can make a world of difference in the cup.