What to Consider When Making Cold Brew Coffee? Why Does Finer Grinding Make Cold Brew Coffee Weaker?

Recently, FrontStreet Coffee received a private message from a customer who wanted to make a more concentrated cold brew coffee. They adjusted the grind to a very fine setting, but surprisingly, the cold brew coffee tasted much weaker than before! This left them puzzled - why did making the grind finer result in a weaker coffee?

Normally, if we want to adjust the extraction efficiency when making cold brew coffee, adjusting the grind size is indeed a good method! However, we cannot apply conventional grind adjustment theories directly to cold brew coffee. The conventional theory states: if you want to reduce extraction efficiency, you should grind coarser; if you want to increase extraction efficiency, you should grind finer! This is primarily achieved by controlling the total surface area of the coffee grounds to adjust the extraction rate. The finer the grind, the greater the total surface area, and the greater the surface area, the easier it is for hot water to penetrate and extract rich coffee compounds!

Why Cold Brew is Different

So why doesn't this theory work well for cold brew? The answer is actually quite simple. Let's look at an experiment conducted by FrontStreet Coffee!

Extraction Experiment

FrontStreet Coffee will use two different grind sizes to make cold brew coffee and observe the differences between them! The coffee beans used in this experiment are from Costa Rica·Baha. When used for pour-over coffee, the grind setting is 9.5 on the EK43. For cold brew coffee, it needs to be 0.5 finer, which would be 9 on the EK43! Then we'll prepare another batch with an even finer grind for comparison. The extraction parameters are as follows:

Coffee amount: 20g
Grind settings: EK43 #9 & EK43 #8

Coffee-to-water ratio: 1:10 (200ml)
Refrigeration time: 8 hours

After refrigeration, we filtered both batches and tested their concentrations! The results were as follows: the regular grind Baha cold brew had a concentration of 2.3%, while the finer grind Baha cold brew had a concentration of 2.1%. As you can see, the finer grind did indeed result in a slightly lower concentration. The reason for this lower concentration is actually quite simple - during the cold extraction process, the coffee remains in a static state for an extended period. Initially, when the coffee grounds come into contact with water, most of them float on the surface of the liquid! As the steeping time increases, these floating particles gradually become saturated with water, and at this point, they begin to sink due to the increased weight.

The coffee grounds that sink to the bottom will exhibit different extraction efficiencies depending on their particle size! Coarser coffee grounds, due to their uneven and larger particles, have numerous gaps when piled together, allowing water to pass through and providing ample extraction space. In contrast, finer particles, being smaller, can fit together perfectly with other particles, forming clumps that significantly reduce the surface area exposed to water, leading to lower extraction efficiency. Therefore, they extract more slowly than coarser grounds! This explains why, despite the finer grind, the resulting coffee concentration was actually weaker than that of the coarser grounds.

Recommendations from FrontStreet Coffee

Therefore, FrontStreet Coffee suggests that while grinding finer is indeed a good method to increase concentration, please avoid making drastic adjustments. After all, we cannot regularly shake or stir it during the brewing process, which would be too tedious for cold brew preparation. So, when you're having difficulty controlling the grind size, reducing the coffee-to-water ratio or extending the refrigeration time can also increase the concentration of your cold brew coffee! If it becomes too strong, you can also dilute it with ice cubes! Remember, you can always dilute coffee that's too strong, but if it's too weak, there's no saving it!

FrontStreet Coffee
10 Bao'an Front Street, Yandun Road, Dongshankou, Yuexiu District, Guangzhou, Guangdong Province

Important Notice :

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FrontStreet Coffee Address: 315,Donghua East Road,GuangZhou

Tel:020 38364473