Why is there a layer of oil floating on the cold coffee? Extraction principle of cold-extracted cold-brewed coffee

In the hot summer, with the somatosensory temperature soaring day by day, the backstage asked Qianjie a lot of questions about cold extraction production.

Cold-extracted coffee is one of the easiest ways to brew coffee at home, as long as it has a sealed container and enough low-temperature extraction environment, after several hours of soaking, you can get a cup of full-flavored coffee. There is no need for tedious steps and techniques, and the production cost is still low. Even beginners can carve delicious iced coffee at home. Cold extraction is not only the first choice for the lazy party to make coffee, but also everyone's "savior" in the hot and scorching heat.

Among the many problems, one partner said that his cold coffee did not seem to be very clean, and there was always a layer of oil floating on the surface, suspected that the coffee had gone bad, or because he did not clean the utensils.

When it comes to "oil", you may immediately think of Crema on top of espresso. This layer of "oil" is formed by carbon dioxide wrapped in insoluble oil in coffee under high temperature and high pressure. As for the "oil" floating on the cold extract, it is due to the performance of the oil in the coffee after condensation at a low temperature.

It is well known that cold extraction requires very low requirements for containers for soaking coffee. It can be a specially designed cold extraction kettle, a finished mineral water bottle, a teacup with a lid, or even a pressure kettle. Anyway, as long as it is dry and clean and can achieve tightness, any bottle and can can act as a "cold extractor".

There are also many options for filtering coffee dregs, such as the built-in filter of the cold extraction pot, metal filter, filter paper and flannel filter cloth. If the size of the filter pore structure is different, the particulate matter that can effectively block is also different.

Like Qianjie uses the Japanese asvel brand cold extraction kettle, the size of the screen hole is 245 mesh, the fineness is high, but there is still fine powder and very fine powder precipitation. If it is not filtered again, there will be a layer of floc gloss on the liquid surface. The flavor of the coffee is not much different from that after filtration, but the roughness left on the tongue when swallowing is relatively obvious, and there are some visible powder dregs at the bottom of the cup.

In order to have a better drinking experience, Qianjie will use higher density filter paper to sift through it. The filter paper of moderate thickness can not only effectively filter the fine coffee powder, but also block more than 80% of the coffee oil. The smooth "customs clearance" of the oil will form an extremely thin layer of oil, which is difficult to observe with the naked eye.

Qianjie will put the cold-extracted coffee liquid filtered again into the refrigerator and refrigerate for 3-4 hours, waiting for the flavor to further precipitate. In this way, the cold extract drink the flavor is very full, the taste is clearer, the acid quality is more transparent.

Finally, Qianjie nagged that the cleanliness of utensils should not be ignored after each cold extraction. Many friends are used to "slacking off" and rinse directly under the tap water at will after use, thinking that it is clean enough. In fact, the condensed coffee oil tends to stick to the built-in filter of the cold extraction pot, and if it is not scrubbed and cleaned for a long time, the pot will form a "fuel consumption smell", thus affecting the cleanliness of the coffee. So, when you use it frequently, clean it carefully on a regular basis.

-END-