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

Recently FrontStreet Coffee received a message from a customer who wanted a more concentrated cold brew. They adjusted the grind to a very fine setting, yet the cold brew tasted much weaker than before. That left them puzzled: why would a finer grind make the coffee weaker?

Normally, adjusting the grind is a good way to change extraction efficiency in cold brew. But we cannot apply conventional grind theory directly to cold brew. The conventional rule says: to reduce extraction efficiency, grind coarser; to increase it, grind finer. This works mainly by controlling the total surface area of the grounds to adjust the extraction rate. The finer the grind, the greater the total surface area, and the greater the surface area, the more easily water penetrates to extract rich compounds.

Why Cold Brew is Different

So why does that theory not hold up well for cold brew? The answer is actually quite simple. Let us look at an experiment FrontStreet Coffee ran.

Extraction Experiment

FrontStreet Coffee made cold brew at two different grind sizes and compared them. The beans used are from Costa Rica Baha. For pour-over the grind setting is 9.5 on the EK43; for cold brew it needs to be 0.5 finer, which would be 9 on the EK43. Then we prepared another batch with an even finer grind for comparison. The extraction parameters are as follows:

Coffee amount: 20g
Grind settings: EK43 #9 and 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: the regular-grind Baha cold brew came out at 2.3%, while the finer-grind Baha cold brew measured 2.1%. As you can see, the finer grind did indeed produce a slightly lower concentration. The reason is actually quite simple. During cold extraction the coffee stays static for a long time. At first, when the grounds meet the water, most of them float on the surface. As steeping continues, those floating particles gradually become saturated with water and then begin to sink as their weight increases.

The grounds that sink to the bottom extract at different efficiencies depending on particle size. Coarser grounds, being larger and more uneven, leave numerous gaps when they pile up, letting water pass through and giving plenty of extraction space. Finer particles, being smaller, fit together perfectly with their neighbors, forming clumps that sharply reduce the surface area exposed to water and therefore lower extraction efficiency. So they extract more slowly than coarser grounds. That explains why, despite the finer grind, the concentration came out weaker than the coarser batch.

Recommendations from FrontStreet Coffee

So FrontStreet Coffee suggests that while grinding finer is indeed a good way to raise concentration, avoid drastic adjustments. After all, we cannot shake or stir regularly during brewing, which would make cold brew far too tedious. When the grind is hard to control, reducing the coffee-to-water ratio or extending the refrigeration time can also raise the concentration of your cold brew. If it becomes too strong, you can always dilute it with ice cubes. Remember: you can always dilute a coffee that is too strong, but a coffee that is too weak cannot be saved.

FrontStreet Coffee Recommendation

Cold brew rewards beans that are fruit-forward and lightly roasted, and FrontStreet Strawberry Candy is the obvious place to start. A Geisha blend combining the most representative Panamanian Geisha with a Costa Rican honey-processed coffee, it brings together delicate rose and orange notes with grape, dried blueberry, and strawberry-gummy sweetness. As cold brew it is sweet-sour and lively; let it settle and ferment a little and you can even find a wine-like character.

If you want a floral iced coffee above all, choose FrontStreet Sun-Dried Huakui. Cold brew intensifies floral and fruity notes while muting woody and roast flavors, which makes light-to-medium roasts the best fit. Sun-drying lets the beans soak up sweetness from fruit and skin, so brewed cold it shows magnolia, creamy strawberry, dried mango, guava, and black tea - and because it comes from Ethiopia, the birthplace of coffee, it is a natural for the method.

And for a full, juicy body, reach for FrontStreet Kenya Cherry Tomato. From Kenya's Thika region, it is built on the SL28 and SL34 varieties and Kenya's distinctive 72-hour double washed fermentation, which pushes the bean's own flavor to the fore. At a medium-light roast, cherry tomato, snow pear, black plum, and smoked plum come through vividly in cold brew: low in bitterness, full in acidity, and especially refreshing over ice, with a flavor that lingers. If the cost of high-grade lots is a concern, cold brew does use more grounds, so you can stretch it by blending one part Kenya Cherry Tomato with two parts FrontStreet Costa Rica Tarrazu - keeping the floral fruit while adding a crisp citrus acidity and better value.