How Does the Espresso Machine Work with Three Variables?

Adjusting an espresso recipe comes down to three things: weigh the coffee grounds, measure the total weight of the espresso liquid, and record the full preparation time. A common base recipe uses 20 g of grounds, 40 g of liquid, and 25 to 30 seconds. Grind size is the only lever for changing the recipe once dose and yield are set.

Under-extraction, from too short a brew time and fast flow, tastes thin with prominent acidity. Over-extraction, from too long a time and slow flow, tastes bitter and can turn metallic. Understanding how does the espresso machine work means balancing sweetness, acidity, and bitterness in the cup. The golden extraction range of 18 to 22 percent can be measured with a refractometer.

For baristas who work with espresso machines every day, adjusting the espresso recipe is an all-too-familiar daily task. Only through repeated tasting and fine-tuning of the grind size and coffee-to-water ratio can you produce a truly satisfying cup. This article starts from the basic principles of extraction, introduces the three core parameters of recipe adjustment—dose, yield, and extraction time—and explains why grind size is the only lever for changing the recipe. It also explores the origin of the golden extraction range of 18–22% and how to scientifically measure extraction results with a refractometer. Whether you are a coffee professional or a seasoned enthusiast, these methods can help you optimize your espresso recipe more rationally.

For professional barista exchange, please follow Coffee Workshop (WeChat public account: cafe_style)

The first thing every barista does before opening shop is often to adjust the parameters for making espresso. Only by tasting again and again and making fine adjustments to the grind coarseness and water ratio can you get a truly satisfying shot of espresso.

Adjusting the espresso recipe is actually not complicated.

The Basic Principles of Coffee Making

What is the essence of extraction? It is using the right approach to balance all the flavors in the coffee. Generally speaking, if the brewing time is too short and the water passes through too quickly, the coffee will taste thin with prominent acidity, indicating under-extraction; conversely, if the time is too long and the flow rate is too slow, the coffee will taste bitter and may even carry a metallic flavor—this is over-extraction. Whether it is single-origin or blended beans, you must find the most suitable degree of extraction so that sweetness, acidity, and bitterness coexist harmoniously while ensuring a rich, smooth mouthfeel.

Adjusting the espresso recipe is actually very simple!

When designing a recipe, you need to do three things:

1. Weigh the coffee grounds

2. Measure the total weight of the espresso liquid

3. Record the entire preparation time

Here is the espresso recipe I commonly use:

- 20 g coffee grounds

- 40 g total espresso liquid weight

- 25 to 30 seconds preparation time

This is a general-purpose base recipe; when encountering coffee beans of different quality, corresponding adjustments still need to be made according to the actual taste.

Rethinking the Traditional "30 ml" Rule

I cannot say this statement is completely wrong, but the reality is that the total volume of espresso liquid changes with the thickness of the crema layer, and the thickness of the crema depends on how long the coffee beans have been stored and how long it has been from preparation to drinking, so measuring by volume is not precise enough. By contrast, weight does not change.

When formulating a recipe, you need to pay attention to the following points:

1. Prepare an electronic scale and a timer

2. Use tools to weigh and record the coffee grounds weight, total espresso liquid weight, and preparation time

3. Taste promptly; if the flavor is satisfactory, record the recipe for this cup of coffee

4. Make everyone on the team familiar with this recipe for easier daily operation

5. Continuously optimize the recipe

Adjusting the espresso recipe is actually very simple!

The Principles Behind Recipe Adjustment

Espresso is supported by three things together: coffee, water, and pressure. Coffee grounds are loaded into a small perforated bowl—the portafilter—and water, under high pressure (usually 9 bar), passes through the coffee bed to extract the essence.

When adjusting a recipe, we often use the following professional terms:

Dose: the weight of coffee grounds loaded in the portafilter.

Yield: the weight of espresso liquid that finally flows into the cup.

Extraction time: the time it takes for water to pass through the coffee grounds to complete extraction and produce a set amount of espresso liquid.

Recipe: combining the above parameters together forms the recipe that baristas follow every day when making coffee. For example, a barista might say: "My recipe is 18 g dose, 36 g yield, and 25 to 30 seconds extraction time."

Doesn't that sound pretty simple? If you are not a barista, you might think: "What's so hard about that? Why does the barista spend so long every morning doing such a simple thing?"

Then let me ask you a question: if your recipe tells you the extraction time is only 10 seconds, what would you do? Without professional training, you definitely would not know where to start. Baristas all understand that the only way to shorten the extraction time is to adjust the grind size. Grind size is extremely critical to making espresso, because for any recipe, if you want to change other parameter settings, you can only do so by adjusting the grind parameter.

Adjusting the espresso recipe is actually very simple!

Why Grind Parameters Are So Important

In roasted coffee beans, only about 30% of the substances are soluble. If you do not grind them, you might have to wait several months to complete extraction, and I am really not sure whether whole beans steeped in water can dissolve at all. To make extraction convenient, we need to grind the coffee beans. Grinding breaks down the structure of the beans and greatly increases the contact area between water and coffee. Typically, the extraction yield of espresso is between 18% and 22%.

Why is it so low?

Because not all soluble substances taste good.

Extract too much, and the coffee becomes bitter; extract too little, and it becomes too sour. So why 18% to 22%? Because Dr. Earl E. Lockhart found through long-term research that the most well-liked coffees all fall within this extraction range.

You might ask: "How do I know how much coffee I have extracted?" You need a professional tool called a refractometer, which can measure the total amount of soluble substances in water and thereby calculate how much of the solution is coffee and how much is water. Based on these data, with a simple calculation, you can determine the coffee's extraction yield.

Recipe Adjustment: What Exactly Are You Adjusting

When a barista says, "I am adjusting the recipe," on the surface he is ensuring that all parameters bring the coffee's flavor to its best state, but in essence he is adjusting the grind parameters. Every barista has different recipe preferences: some like an 18 g dose and 36 g yield, while others prefer an 18 g dose and 40 g yield; some are used to a 25 to 30 second extraction time, while others prefer 30 to 35 seconds. No matter how the recipe is set, our ultimate goal is to bring the coffee's flavor to the expected level and the quality to its best.

So, isn't it simple? Go ahead and adjust your espresso recipe yourself!

The above content is compiled by CoffeeHunters, a coffee news website.