PREPARATION OF FILTERED COFFEE

 

Basic Principles

Before going into detail about brewing, we’d like to cover the core principles of coffee extraction. Brewing coffee is always a delicate game — balancing the quantity of coffee, the quantity of water, the type of grind, and the extraction time. Depending on the method, these factors can be varied in order to highlight specific attributes of a coffee. 

Remember that a coffee drink is typically around 1.5% coffee and 98.5% water — any minor change can radically alter the end result.

If you increase one end of the equation, you must lower the other, and vice versa. For example, if you are working with a fine grind, and the coffee is getting over-extracted, you can reduce the amount of coffee you are using, holding constant the water temperature and the extraction time. Another example: if you are working with a lower water temperature, you should increase the extraction time and keep the other variables constant. And so on.

Here, in more detail, are the central factors impacting the brew:

COFFEE GRIND

A coffee’s grind determines the amount of the bean’s surface area exposed to water. The finer the grind, the more surface area exposed to water — and the more intense the extraction. The grind should correspond to the method and time of infusion for optimal extraction. The faster the infusion, the finer the grind. The slower the infusion, the coarser the grind.

Although there are many grades of grind, we divide them into three main categories:

Fine grind

Is the smallest grind you can produce and has a dust-like quality. This is how we grind beans for espresso, moka or ibrik. Extraction time (duration of contact between coffee and water) for these methods is very short, requiring particles to have more surface area exposed to the water.

Medium grind

Is used for drip methods like Chemex, Syphon, Aeropress, V60, traditional coffee pots, and even for coffee tastings. Since it does not leave as much surface area exposed to the water, medium grind is used for coffees brewed over a slightly longer extraction time (approximately 2 to 4 minutes).

Coarse grind

Is commonly used with steeping methods, where grounds are immersed in water for 4 minutes or more — as is the case with French Press or Cold Brew.

(Fine powder, like flour)

(Sand-like grains)

(Like sawdust)

Water Temperature

The higher the temperature, the greater the quantity of soluble coffee solid that can be dissolved in the extraction. Normally, with the exception of Cold Brew, we recommend using water just below boiling point, which, in the case of Medellín, is 95 degrees Celsius (203 degress Fahrenheit). If water temperature is below this level, more time is required for a proper extraction.
In addition to hydrogen and oxygen, water also contains minerals that it brings to the extraction — the optimum level being 120 particles per million.

Proportion Of Water to Coffee

Proper extraction requires a delicate balance between the amount of water, and the amount of coffee. At Pergamino, we work within a range of between 12 and 15 ml of water per gram of coffee — depending on the type of coffee, its roast, extraction time, brewing method and filter. Given the variability of the water / coffee relationship, we are always experimenting with different proportions when working with a new coffee.

EXTRACTION TIME AND BREWING METHOD:

Time and method of extraction go hand in hand, since extraction time varies according to the method and filter used.


Here are two families of slow filtrates:

Steeping:

Coffee is immersed in water for a period of time, before the drink is strained through a filter to separate out the grounds.

 

– Steeping methods require a coarser grind than drip methods, since the grounds are in direct contact with the water for a longer period of time.

Drip

In drip methods, coffee is extracted as water passes through the grounds with the pull of gravity, and is strained through a filter that separates out the coffee particles.

– Drip methods require a medium grind, as the coffee is only in contact with the water for a few seconds. In order for extraction to take place rapidly as the water passes through, more surface area of the grounds must be exposed.

TYPES OF FILTERS:

– Perforated metal trays (Moka).
– Woven wire mesh (Evasolo, French press).
– Cloth (Greca).
– Paper of different densities (Chemex, automatic drip coffee machines, V60, Aeropress, Siphon, among others).

TURBULENCE:

The way we add water to coffee grounds greatly influences the final result due to the level of turbulence we create while pouring. This is particularly important in drip methods, where we pour the water in a circular manner to create a swirl, and the coffee grounds move in contact with the water. In some cases, we also use a stirrer to generate turbulence and move the grounds around.

PRE-INFUSION/BLOOM:

Pre-infusion (or bloom) is the first contact between coffee grounds and water. In this first quick pour, we add just enough water to moisten the grounds and release the CO2 that still remains inside the beans after roasting. Think of this process as a rapid degassing. You should add double the amount of water as coffee. For example, if a Chemex uses 32 grams of coffee, you should add about 64 ml of water.

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