Principal Brewing Theories

When it comes to brewing coffee, there exists a multitude of ways from which one can choose to brew coffee. Be it from the espresso machine that we are all to familiar with, to French presses, moka pots, cold brew, or - you name it, any of the coffee brewing appliances that are out there!There are, however, two fundamental ways to think of brewing coffee: Percolation, and Immersion.

By understanding these two methods, it will help to better identify the brew methods that go behind each type of brewing equipment, and therefore provide a better understanding of the factors that may affect each brew, and even the expectations and approach (e.g. grind size, brew times) to brewing using different devices.

I like to think of the methods as differentiated by three main aspects:

1. The ratio of water to coffee beans used.

2. How finely one would grind the coffee beans

3. Duration of brew timings in each method.

In this vein of thought, there then exists a third method that is a unique subset from Percolation - brewing coffee with an espresso machine. For me, this falls into a third method completely on its own, which people often term as brewing using Pressure.

Percolation

The most common example of a coffee brewed via percolation is the pour over coffee. This method of brewing coffee works by using gravity to extract compounds out of the ground coffee as water passes through it.

Coffee beans are usually ground to medium/fine, helping to extend the brew time as water passes through the coffee, ensuring sufficient extraction.

As extraction is fast, brew times for percolated coffee generally range from 3-4 minutes.

Immersion

Immersion coffee is the steeping coffee grinds in water, relying on diffusion to extract compounds out of these grinds to create coffee. This method has multiple variations, ranging from the typical French press, to Turkish coffee, and even the popular cold brew - all of them utilize immersion to brew coffee.

Using the most common method in the market, the French press, as an example, immersion coffee typically grinds coffees coarsely. With Immersion, extraction rates slowly decline as the concentration between coffee grinds and the brewed water gradually even out.

The gradually diminishing extraction usually calls for an initially hotter water, brewed for approximately 4 minutes, to get an ideal cup of coffee.

Immersion coffee is interesting in that, depending on the brewing equipment and style of brewing involved, grind size and brew times vary widely. Turkish coffee is known to use extremely fine coffee powder over a brew time of 3-4 minutes, while on the other hand, cold brews often use very coarse grinds, steeped with water overnight (lower extraction rates due to colder water, but longer brewing times).

Pressure

The espresso machine stands as a method on its own in brewing coffee for the simple fact that it is so unique - hot water is pushed through a puck of coffee grinds at 9 bars of atmospheric pressure to obtain coffee, in what can be thought of as an extreme version of Percolation.

This method has a very high extraction, and often calls for coffee to be ground extra fine to achieve a good amount of extraction within the short brew time of about 20-30 seconds.

Backward compatibility of roasts:

One example of how we can apply the knowledge of the different brewing methods is in determining the types of brewing methods suitable for a particular coffee bean, or a bag of ground coffee that is sitting at home unused since it was last gifted at Christmas.

In most circumstances, backward compatibility of roasts presents as a good guide to identifying which brewing methods may work with certain coffees.

A darker roast, while often used for pressured brewing, can still be brewed using all three methods, whereas the lighter the roast, the more likely that it will perform better in brewing methods involving lower extraction rates, such as percolation via a pour over.

The grind size of pre-ground coffee also gives insight into what adjustments a brewer might need to take to brew it in a certain method. For example, a finely grounded bag of coffee brewed on a French press would call for a slightly shorter brewing time as well as more careful filtering to obtain the same clean cup of coffee that one may be normally used to.

Final note

The Speciality Coffee Association (SCA) defines the ideal cup of coffee to have an 18-22% extraction yield, wherein a good balance of acids, sugars and bitter roasted compounds is achieved for a good tasting cup.

Knowing the different methods of brewing allows us to understand the rationale behind why some factors like grind size and brew times are calibrated in certain ways, and this also further allows us to easily adapt between brewing methods to achieve well extracted, and good tasting, coffee - that is, after all, the end goal of every barista and home brewer alike.