The extraction problem of Italian concentration, how to do Italian concentration

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Overextraction (Over-extraction)-the concept of extraction rate must first be understood. According to the measurement standard of VST Coffee Refractometer (coffee refractometer, the official designated measuring instrument for a number of coffee international competitions), the reasonable coffee extraction rate (extraction yield) is between 18% and 21%. Of course, there are coffee people (such as Matt Perger) who pursue an extraction rate of slightly higher than 21%, but generally speaking. If the actual extraction rate exceeds the ideal extraction rate of this coffee bean, that is, the problem of over-extraction occurs. The roasting degree, variety and situation of each coffee bean are different, and the same extraction rate may be suitable for light-roasted Kenyan SL-28, but not for medium-roasted Brazilian Bourbon, light-roasted Bolivian Typica or a certain formula bean. Excessive extraction often leads to dark coffee liquids and oils (Crema), sometimes producing obvious air bubbles floating on the liquid surface, usually taking too long to extract (for example, more than 1 minute), and more than 10 seconds to see the first drop of coffee liquid. There are many reasons for excessive extraction, the common ones are: coffee powder is too fine grinding, water temperature is too high, extraction pressure is too high, filling pressure channel is too strong, and so on.

Underextraction (Under-extraction)-in contrast to overextraction, underextraction usually means that there are still many unextracted aromatic molecules in coffee powder, but the preset extraction time is over, that is, the commonly known extraction rate is less than 18%. When the extraction is insufficient, the coffee liquid may have a light yellow color and lack of coffee oil. the extraction time is usually too short (for example, the extraction is completed in 15 seconds), and the coffee is released like a stream of water under pressure. instead of the sticky feeling of honey flowing down during normal extraction, the above phenomena are all signs of insufficient extraction. There are many reasons for insufficient extraction, such as coarse grinding of coffee powder, low water temperature, insufficient extraction pressure, light filling pressure and so on. The taste is often with strong and astringent fruit acid, salty taste, water feeling and lack of due sweetness.

Uneven extraction (Uneven Extraction)-extraction is usually a combination of over-extraction and uneven extraction, the more common are: channel effect (Channeling), side channel effect (Side Channeling), doughnut extraction (Donut Extraction, or Edge Channeling outer ring channel effect) and so on.

The channel effect occurs at a certain point or block at the bottom of the filter cup, and there may be many reasons, such as the mixture of new and old powder after adjusting the bean grinder scale, uneven powder and Distribution, caking of coffee powder, etc. If you use a bottomless handle, you can see that the block is dark and no liquid flows through the initial stage of extraction. Sometimes there is a water column ejected because the pressure is too large and the range of water can pass through is very small. the influence of this phenomenon on the flavor can be great or small, depending on the scope and degree of the channel effect, and the greater degree will produce bitter, astringent and other defective flavor.

The side channel effect is a very serious channel effect, which is usually caused by the uneven force between the left and right or the front and back of the Tamping, or it may also be caused by the deviation of the water flow in the head. During observation and extraction, we will find that the coffee flow rate is too fast while the coffee flow rate is too slow, the flavor is usually very bad, and all kinds of defects may be concentrated in this cup, such as bitter, dry, sharp sour, salty taste, and so on.

Doughnut extraction is usually a phenomenon that the outer ring extraction is faster and the central extraction is obviously too slow. like the side channel effect, it usually produces all kinds of defective flavors, if not very serious, this phenomenon will not be seen after 15 seconds of extraction, but do not think that the next coffee liquid column (Stream) seems to be normal extraction will not be a big problem, because when the extraction is in the middle. The coffee liquid in the outer ring has begun to increase and accumulate to the center, so the extraction difference between the center and the outer ring cannot be observed, but in fact, the uneven extraction continues, so don't be blinded by the appearance. This problem is usually caused by the fact that the coffee powder is compacted in the center, the outer ring is loose, or the quality of the filter cup itself is poor and the bottom is not flat. The shape of the bottom of the filler (Flat v. s. Curve) can sometimes improve this problem.