What is the best grind size for cold brew?

Cold brew is a unique extraction method that relies on time rather than temperature to pull flavor from the coffee. Because you are using cold or room-temperature water, the extraction process is much slower and less efficient than hot brewing. This is why we use a much larger ratio of coffee to water and a significantly coarser grind size to balance the extraction.

When you grind your coffee for cold brew, you want particles that are large and uniform. If the grind is too fine, the water will extract too much of the coffee's bitter compounds and tannins during the long 12-to-24-hour steep. This leads to a 'muddy' concentrate that is difficult to filter and leaves a harsh, drying sensation on the palate. A coarse grind ensures that the water extracts the sweet, chocolatey, and nutty notes while leaving the harsher, more soluble bitter compounds behind.

Consistency is key, even with a coarse grind. Using a burr grinder is highly recommended because it produces a uniform particle size. If you use a blade grinder, you will inevitably get a mix of large chunks and 'fines' (dust). These fines will over-extract during the long steep, potentially introducing the very bitterness you are trying to avoid. If you must use a blade grinder, try to pulse it in short bursts and shake it to keep the grind as even as possible.

In practice, start with a coarse grind and a 1:8 or 1:10 coffee-to-water ratio. If your cold brew tastes weak, try steeping it for a few hours longer rather than grinding finer. If it tastes too bitter, shorten the steep time or use a slightly coarser setting. Cold brew is incredibly forgiving, but getting the grind size right is the foundation for a smooth, clean, and refreshing concentrate that you can dilute to your exact preference.