Espresso Extraction: Ratios, Time, and Key Considerations - Brewing Methods and Flavor Characteristics

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What is Espresso?

Espresso was invented in Italy. Since the early 20th century, this method of using steam pressure to create beverages has been successfully commercialized, becoming today's widely popular coffee brewing method.

The Extraction Principle of Espresso Coffee

When we use any method to brew coffee, our goal is to extract the positive flavor compounds from the coffee beans through water, thereby obtaining delicious coffee liquid. Coffee beans are composed of various substances, with about 30% of their components being water-soluble, such as fruit acids, caffeine, oils, and carbohydrates. Only about 20% of these are positive-tasting aromatic small molecules that are extracted first; the remaining large molecules with woody and bitter tastes require longer extraction times. Therefore, the barista's job is to adjust corresponding parameters to extract more high-quality components from the coffee.

Espresso was developed by Italians to extract a strong cup of coffee in the shortest possible time. It uses steam pressure to compress coffee grounds within dozens of seconds, extracting soluble aromatic compounds. Due to this short extraction time and high-pressure environment, the concentrated flavor expression is more intense. To produce a good espresso, operations must be more rigorous, with every influencing parameter requiring careful consideration.

There are many factors that affect the flavor from coffee beans to coffee liquid, including grind size, espresso machine boiler pressure, water temperature, distribution and tamping pressure, dose amount, extraction time, and extracted liquid weight. Typically, the machine's pressure and water temperature are set and not easily changed. Distribution and tamping pressure depend on the barista's habits. The four main factors used in daily extraction adjustments are dose, time, liquid weight, and grind size.

Grind Size

The coarseness and uniformity of the grind are the most important factors affecting flow rate variations between each espresso. Even a 1-gram difference in dose can result in several seconds difference in flow time for extracting the same amount of espresso liquid. When coffee particle sizes are uneven, areas with higher density after tamping create greater resistance to water flow, making extraction distribution inconsistent. The grind directly affects coffee liquid flow rate, time, and flavor changes.

Dose-to-Liquid Ratio

The ratio between dose and extracted liquid weight is what we commonly call the dose-to-liquid ratio, which is a relatively intuitive extraction parameter. The dose depends on the capacity of the portafilter basket, divided into double and single sizes. For example, FrontStreet Coffee's shop machines use 20 grams for double shots, making adjustments based on this parameter (accurate to 0.1 grams). Since the dose-to-liquid ratio is not fixed, the coffee output volume should be determined by the flavor performance.

Previous baristas didn't have precise scales and would directly observe the color changes in the crema to determine the output volume. At the beginning of extraction, it appears dark brown and quite concentrated; as time progresses, the color gradually shifts to golden yellow, then to light yellow. Generally, extraction should stop when the crema turns white, indicating the need to end extraction. Today's espresso extraction standards are more rigorous, with more stable data summarized, and dose-to-liquid ratios tend toward a fixed reference value of 1:2. For example, FrontStreet Coffee's shop uses 20 grams of coffee grounds to extract 40 grams of liquid.

Extraction Time

Time is affected by factors such as grind, dose, and whether the coffee grounds are uniform, while also influencing flow rate and dose-to-liquid ratio. Generally, espresso extraction time is between 25-30 seconds. With a determined dose-to-liquid ratio, shorter extraction times mean faster flow rates and fewer dissolved coffee compounds; longer extraction times mean slower flow rates and more dissolved coffee compounds. With the same dose-to-liquid ratio, changing extraction time can only be achieved by adjusting the coffee's grind size and dose.

In daily extraction, to control concentration and extraction rate within ideal ranges, baristas generally judge based on espresso flow rate and resulting taste, then adjust two parameters: grind size and dose-to-water ratio. For example, with the same extraction ratio, if espresso shows negative flavors like burnt bitterness but has moderate concentration, this might be due to extraction time being too long, causing burnt bitter flavors to be extracted. The general solution is to make the grind coarser to speed up the flow rate. When espresso tastes weak and has low concentration, it might be under-extracted, which can be improved by increasing the dose or making the grind finer to enrich the mouthfeel.

What Other Operational Details Need Attention?

All the above parameters change correspondingly with the extraction state. We need to pay more attention and summarize the adjustment directions brought by extraction variables to better grasp the excellent flavors in the cup of coffee.

Regardless of which barista, to extract a high-quality espresso, every action must be precise and well-executed. Distribution must be even, and tamping pressure must be stable. If pressure is too low or the coffee bed is uneven, it will lead to uneven extraction. Inserting the portafilter requires proper alignment; if it hits the coffee machine, it can shatter the puck, causing channeling and making the taste difficult to swallow.

After extraction, some coffee residue will stick to the shower screen. If not cleaned, it will be dried by the high temperature of the group head, and these coffee residues will affect the flavor of the next espresso. Therefore, FrontStreet Coffee suggests we develop a habit: after extraction is complete, remove the portafilter while simultaneously flushing the shower screen with water.

Recommended Espresso Coffee Beans

Since espresso is extracted under fine grinding, high water temperature, and high pressure, the concentrated coffee gathers multiple flavors, with various flavor compounds impacting our taste buds exponentially. Therefore, if we use light-roasted single-origin coffee beans for extraction, the taste might be too strong and overwhelm the coffee's aroma. Coffee, as an agricultural product, varies with climate, soil, and other factors. Even from the same region, each batch of coffee beans will have different flavors. Blended coffee beans use the principle of complementing strengths and weaknesses to ensure each batch can express balanced and stable aroma and mouthfeel.

To help espresso release rich golden crema and create Italian coffee with mellow, aromatic mouthfeel, we recommend FrontStreet Coffee's Classic Italian Blend. This is a dark-roasted coffee combining Brazilian natural-processed, Indonesian Mandheling, and Vietnamese washed beans. Besides its burnt aroma, the key feature is full crema. Whether made into Americano or latte, it can easily present these advantages.

A freshly made espresso is covered with a thick, dense golden foam called crema. This is the result of carbon dioxide from freshly roasted coffee beans foaming under the high pressure inside the coffee machine. Crema is not only full of aroma but also an essential element for creating latte art in milk coffees. To ensure everyone can drink fresh, aromatic coffee and enjoy the most complete flavor experience, FrontStreet Coffee only ships coffee beans roasted within 5 days.

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