Coffee is water with whatever we manage to extract from coffee beans. Here I try to structure my thoughts on what makes a coffee, that the individual likes.

How can coffee taste?

There's a plethora of words describing a specific kind of coffee, whereas espresso is the basis of many of them. Some notable mentions:

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

Many drinks dilute and mix the raw coffee taste, which is great. However, to adjust the coffee-related flavors in those drinks we need to break down the process of making espresso.

There are also other coffee brewing methods such as the Bialetti / Moka pot, the French Press, pour-over coffee, etc. Understanding espresso will help us dive into those.

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. For such, distribute the pull into three cups. The first cup will be sour and the last one should be bitter or more watery.

Sour: Reminiscent of lemon juice. Result of acidity. The sharp flavor is detected on the sides of the tongue.
Bitter: Reminiscent of dark chocolate. 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 determined the right process parameters. My goal is being able to get the most out of each bag, by knowing how to adjust my process parameters. Accordingly, all other chapters should be bean-independent. On that note, when detecting bitterness in our shot, it's important to remember that some coffees can have a subtle bitterness 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 at a maximum of a few minutes before pulling the espresso.

Espresso

What differentiates espresso from other coffee-brewing methods is that the nearly boiling water is forced through the coffee grounds 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
• How the so-called coffee-puck is prepared.

Determined by the coffee machine:

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

The ideal machine mostly helps you by keeping its process parameters constant, 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 it. Most machines bring 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. I believe (no real experience or research done here), that this influence is one of the latest optimization steps.

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
• Amount of coffee

Both influence the resistance from the hot water to the coffee in the cup. Respectively the time it takes the water to push through the coffee.

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 2:1 brewed coffee: ground coffee ratio (36g out)
• 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.

The remaining adjustment is the grind size, which is the hardest to quantify universally.

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. Or you start diving into slight adjustments of the other parameters and reduce the amount of ground coffee.

Sounds easy enough, right?

Channeling

Backlog

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If we adjust our espresso-making process in time we can utilize two more fancy coffee words:

• Lungo: An espresso pulled over a longer duration
• Ristretto: An espresso pulled over a shorter duration.

Espresso, Bialetti, French press

Order of importance for "good" coffee (Using whole beans, fresh beans, settings/skill, grinder, machine)

Sources, Inspirations and further readings

https://www.baristahustle.com/blog/the-espresso-compass/