Coffee

Coffee Part 1: The basics

At its core, brewed coffee is water with extracts from coffee beans. This page aims to introduce into the process of making coffee at home.

How can coffee taste?

There's a plethora of words describing a specific kinds of coffee, whereas espresso serves as the basis of many.

• Doppio: A double shot of espresso
• Cappuccino: Espresso with steamed milk and foam
• Americano: Espresso and hot water

Coffee variations dilute or complement the raw coffee taste. However, to adjust the coffee-related flavors in those drinks, understanding the espresso extraction process is key.

Coffee-related flavors

A key taste spectrum ranges from sour over "balanced" to bitter. The interesting part is, that where we land on this spectrum heavily relies on process factors. If it tastes sour, you have under-extracted the coffee. If it is bitter, it's over-extracted.
Once you have reasonable process parameters, you can learn to differentiate the tastes by pulling a salami shot. To do this, distribute the espresso shot into three cups as it brews. The first cup will be sour and the last one should be bitter and potentially watery.

Sourness: Reminiscent of lemon juice. Result of acids extracting early in the brewing process. The sharp flavor is detected on the sides of the tongue.
Bitterness: Reminiscent of dark chocolate or even ashy/burnt flavours. Dry. Displeasing taste towards the back of the tongue.

Beans

The beans heavily impact the taste of the coffee. Most often, one can only start exploring the full flavor set of a bean bag after having dialed in the right process parameters. My goal is to be able to get the most out of each bag by knowing how to adjust the process parameters. The logic of the further paragraphs should be applicable to any beans. The absolute process parameters will vary from bean to bean.

When detecting bitterness in a shot, it's important to remember that some coffees can have a bitterness (such as dark chocolate) within themselves without it hinting towards an over-extraction.

Coffee oxidizes. We need to use fresh beans. Ideally, we use them 1-8 weeks after the roast date. The beans are to be ground immediately before brewing the espresso.

Espresso

What differentiates espresso from other coffee-brewing methods is that the nearly boiling water is forced through finely ground coffee under high pressures (6-9 bar). As a result of the high pressure difference with the atmosphere, the coffee gets a characteristic crema (foam) on top.

Process Parameters

We strive to find a process that lets us neither over- nor under-extract the coffee.

Parameters you influence shot-by-shot:

• Duration of the coffee shot
• Coffee-puck preparation

Parameters largely determined by the coffee machine:

• Water temperature
• The pressure of the water
• Diameter of the coffee container (basket)

A good machine is able to keep its process parameters stable, so that you know the change in taste is due to the parameter change you chose to do. Generally, if you are starting the journey, I would not worry about having the perfect machine. Most machines aim for water at around the desired ~93-degree temperature and maintain pressures above 6 bar. I started my journey with a fully manual espresso maker where you pour boiling water on top and managed to get great espresso. Expect the learning curve to be a bit steeper if you decide to go down that route.

That being said, for most machines water temperatures and pressures do vary throughout a shot and also from shot to shot. In my perceptions, the impact of those variations is one of the later refinement steps in perfecting the espresso.

Coffee Puck

The puck is where I believe to find most of the espresso magic that you influence with a given setup. This is where we can influence how much we want to extract our coffee. Key parameters are:

• Coarseness of the coffee: grind size
• Amount of coffee: dose

Both influence the resistance for the hot water to push through the coffee puck. More resistance should result in a slower coffee extraction rate.

Brewing Espresso

Let's start with some experimentally determined, good parameters for standard-sized 58mm baskets.

• Start with about 18g of ground coffee
• Target a 1:2 dose: yield ratio (36g coffee out in the cup)
• Aim for a brewing time of 30 seconds. This means your cup should just reach about 36g at the end of the 30-second pull.

Adjusting the grind size is the primary way to control and the hardest to give quantifieable guidance for.

If the shot pulls too fast and tastes sour: we need to increase the resistance of the coffee puck and thus grind finer. If we barely get any coffee drips out of the machine we have too much resistance. We can grind coarser. Alternatively, you could considerr slightly reducing the dose.

Sounds easy enough, right?

Channeling

Channeling occurs when the resistance of the puck is uneven and water finds paths of least resistance through the puck (channels). This results in overextraction of the coffee in those areas and an under-extraction in the others. The result is both an intensly sour and bitter coffee at the same time. Buargh. With increasing resistance of the puck, the risk of channeling grows.

How can we avoid it?

• Puck prep: Make sure the coffee grounds are evenly distributed.

What's next?

Mastering the concepts above allow you to brew great espresso at home.

My opinionated take on the order of importance to get good-great coffee:

1. Use whole beans and grind them fresh
2. Use fresh beans
3. Understand and apply the extraction dynamics explained here
4. The quality of your grinder
5. The quality of the coffee machine

In a next part we will look at coffee equipment and some more advanced nuances.