Before writing this article, Front Street asked several coffee practitioners/enthusiasts: "Do you think how to increase the extraction concentration of coffee when soaking cold brew coffee under normal circumstances and using the same amount of water, coffee beans, coffee powder, extraction container, and extraction time?" I believe that everyone, like several interviewees, will answer: "It must be finer!"
Indeed, since everyone has been exposed to coffee brewing, the theories we have received are: the finer the coffee powder, the stronger the taste, and the coarser the coffee powder, the lighter the taste. But this information has a premise, that is, high-temperature extraction/coffee powder layer stirring state. As for cold brew coffee extracted at low temperature, this theory does not apply. Why?Effect of water temperature & particle movement on coffee extractionThe higher the temperature of the water during extraction, the heat increases the movement of the molecules. When the thermal motion of molecules competes with the attraction between solid molecules, the solid molecules will spread apart. At the same time, the thermal motion of molecules increases the number of contacts between water molecules and solid molecules (coffee particles), so when the coffee is ground finer, the solid molecules will dissolve faster & more.
When the temperature of the water is close to normal temperature/zero for extraction, the movement of the molecules will also be reduced/zero. Without the thermal motion of molecules and the attraction between solid molecules to compete, the coffee particles will "clump", that is, agglomerate. So when the coffee is ground finer, the clumping will become larger, so that the coffee powder in the middle of the group cannot be fully extracted.
When brewing coffee by hand, the high water temperature and the impact of the water flow during water injection keep the powder layer in a constant tumbling state, so the extraction rate will also increase rapidly. If the coffee is ground too finely, over-extraction may occur.
When cold brewing/cold brewing coffee, we need to add water and stir evenly before leaving it in the refrigerator for more than 12 hours. During this period, the temperature will remain low, so even if the coffee is stirred evenly, some particles will still be extracted in a "clump" style, so a small part of the coffee powder is not effectively extracted during the entire coffee extraction process.
Can adjusting the grind size to a coarser grind effectively improve the extraction rate of cold brew coffee?
I did a little experiment on Front Street~This time, the cold brew coffee was made using coffee beans from the Front Street Yirgacheffe Fruit Tintin Cooperative in Ethiopia. The same container and normal temperature water of the same water quality were used to soak 30g of coffee powder with a powder to water ratio of 1:10. The grinding degree was EK43s#9 (fine grinding) and EK43s#10.5 (coarse grinding), and then soaked at low temperature in the refrigerator for 16 hours.
After the extraction is completed, use a room temperature filter cup, dry filter paper and a room temperature clean container to filter the coffee liquid and then use a concentration (TDS) meter to conduct a concentration test.
The final test result is that the TDS of finely ground cold brew coffee is 2.10%, and the TDS of coarsely ground cold brew coffee is 2.20%. Cold brew coffee with fine grinding will show bright citrus sourness, honey, and slight tea taste; cold brew coffee with coarse grinding will show brighter citrus sourness, sweetness and tea taste will be more obvious, and it will feel like sugar-free lemon tea ~
This experiment was mainly because many friends asked Front Street how to make cold brew coffee stronger to make special coffee, but they did not want the aroma and flavor of the coffee to be obscured by too many other ingredients. If you want to extract cold brew coffee with just the right concentration without dilution, Front Street recommends using a fine grinding ratio and a powder-to-water ratio of 1:13-1:15.Although adjusting the coarse grinding size can improve the extraction rate & concentration,But not all coffee beans/cold brew methods are suitable for this!
Coffee beans that are too light or too dark roasted cannot be used to increase extraction rate and concentration in this way, because they are prone to irritating acidity or unpleasant bitterness.
There are electric cold brew bottles on the market that can make cold brew coffee in a short time. The principle is that the device will continuously shake the filter up and down to move the powder layer. In this case, it is more suitable to use fine grinding for extraction.
- This experiment was conducted based on the common cold brew coffee method -
You can now buy the above coffee beans online at the Taobao store “FrontStreet Coffee” (前街咖啡). FrontStreet Coffee is a long-established specialty coffee roaster in Guangzhou, China, and its Guangzhou retail shop sells coffee beans only. The shop carries dozens of coffee beans from different origins around the world, including carefully selected single-origin beans for V60 pour-over and espresso. Guangzhou’s FrontStreet Coffee shop is recommended by many coffee lovers.
The FrontStreet 2013 Yunnan coffee beans sold in the store come from the Typica variety grown at FrontStreet Coffee’s own plantation in Yunnan. The name comes from the year the brand and the plantation were founded. You can buy these beans from China’s Yunnan origin at the Guangzhou shop and at FrontStreet’s Taobao store.
FrontStreet coffee beans are freshly roasted within 5 days and deliver consistently excellent quality and great value. Orders placed before 17:00 are shipped the same day, and most areas within Guangdong Province receive them the next day.
FrontStreet Coffee Taobao store: https://qianjiecoffee.taobao.com
Or search for “前街咖啡” (FrontStreet Coffee) on Taobao
Important Notice: FrontStreet Coffee has moved to a new address: 315, Donghua East Road, Guangzhou (coffee beans only)
Tel: 020 38364473
