How Many Milliliters in a Shot of Espresso - Common Espresso Extraction Problems and Correct Methods

What is Espresso Coffee?

Espresso, also known as "Espresso," is a coffee beverage originating from Italy or an Italian coffee base, extracted quickly under high pressure. Traditionally, a single shot of espresso contains about one ounce. The international technical standards are as follows: approximately 7 grams of freshly ground coffee powder, using water at around 92°C temperature under about 9Bar pressure, extracted over 20-30 seconds to produce about 20-30ml of coffee, which should be covered with a layer of coffee crema on the surface.

With the development of coffee specialization, some new coffee theoretical knowledge has been revealed, and with the flourishing of numerous independent coffee shops, their espresso extraction methods also have subtle differences. According to FrontStreet Coffee's standard production, making an espresso coffee is based on 2 shots (1 shot) as the standard, using 19g of coffee powder to extract 38g of espresso liquid at a 1:2 ratio, with a time of 28 seconds.

Why have most domestic coffee shops changed their extraction parameters from milliliters to grams?

This relates to the issue of density. In a cup of espresso, you can see dark espresso liquid and floating coffee crema on top. These crema have low density and large volume, and it cannot be guaranteed that the coffee crema in every cup is the same at all times, so changing to weight measurement is more accurate.

How to understand under-extraction and over-extraction in espresso?

Over-extraction often has the phenomenon of dark coffee liquid and crema (Crema), sometimes producing obvious large bubbles floating on the liquid surface. Usually, the extraction time is too long (such as: over 1 minute), and it takes more than 10 seconds to see the first drop of coffee liquid. There are many reasons for over-extraction, common ones include: coffee ground too fine, water temperature too high, extraction pressure too high, tamping force too strong, etc. When tasting, the flavor often has burnt bitterness and astringency.

Under-extraction is the opposite of over-extraction. Under-extraction usually means that there are still many aromatic molecules in the coffee powder that have not been extracted, but the default extraction time has already ended, which is generally known as an extraction rate below 18%. When under-extracted, the coffee liquid may have a lighter yellow color and lack coffee crema. Usually, the extraction time is too short (such as: completing extraction in 15 seconds), and the coffee flows out in large amounts like water under pressure, rather than the viscous feeling like honey flowing down during normal extraction. The above phenomena are all signs of under-extraction.

Common Issues in Espresso Extraction

In addition to these theoretical problems, there are some problems that often occur in extracting espresso, for example:

When using a double-spout portafilter to extract espresso, why does the coffee liquid always drip from one side first?

There are three main reasons for this problem. First, confirm whether the shower screen of the group head is blocked by coffee residue, observe whether the water flow from the group head is evenly distributed, and if you find the water flow偏向一侧, you need to clean the group head and shower screen.

Second, whether the coffee powder is tamped evenly. If one side of the coffee puck is high and the other side is low, it will cause water to penetrate faster to the lower side, resulting in the liquid flowing out from one side first during extraction.

Third, observe whether the coffee machine or table is level with the ground. In many cases, it is found that the first two situations occur, but it is the coffee machine or table that is not level, causing the coffee machine to tilt, so the liquid will flow out from one side first during extraction.

What causes coffee crema to clump?

The production of coffee crema is due to the high temperature and high pressure during the brewing process that combines air and soluble fats in the coffee. If the coffee beans are too fresh, the gas content inside is too high, which will make the crema too rich (thick). Moreover, overly fresh beans are very unstable, and the pressed crema will also be rough and will solidify and clump after being left for a long time.

Therefore, if you find the phenomenon of crema clumping, it is likely that the coffee beans are too fresh. The optimal solution is to store them for a few more days and use them after the bean resting period has passed.

Is the tiger-striped crema on the surface of espresso normal?

Tiger-striped crema refers to dark spots on the surface of the crema, looking like tiger stripes. In fact, the dark spots on the crema are some very fine coffee powders. The reasons may be that the grinder produces too many fine powders, the holes in the portafilter basket have become larger, or the extraction pressure of the coffee machine is too high. Also, coarse grinding combined with heavy tamping can cause fine powders to easily move down and pass through the filter cup into the espresso cup, which will cause dark tiger stripes to appear on the Crema surface, making the Crema color appear darker.

In fact, whether there are tiger stripes or not does not have much impact on the flavor of espresso. Espresso with tiger stripes will have a fuller body, but if there are too many fine powders, it will also have a counter-effect, causing a rough mouthfeel.

Important Notice :

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