For cold brew, it's best to use a medium-coarse grind - one that looks like kosher salt.When making cold brew, the coffee grounds steep in the cold water for more than 12 hours (we recommend 16 hours). A coarser grind helps to avoid removing too many coffee solids (read: flavor) from the grounds too quickly, which would make the cold brew taste overwhelmingly strong and unbalanced. The coarser the grind, the less surface area is exposed to the water, which means that each ml of that cold water won't be able to pull as much flavor out.Interestingly, when coffee shops first started experimenting with cold brew, we thought you needed to go extremely coarse, to the end of the dial on a grinder. We now know that because cold water extracts coffee solids more slowly anyway, we actually don't need to grind as coarse as we once thought (though a grind on the coarse side is still a must), and can extract more pleasant flavors over time if we use a medium-coarse grind.Pro tip: if your coffee is already ground and doesn’t look very coarse, but you really want to make some cold brew, you’d want to modify how you brew in two ways:First, you don’t need to steep for the full 16 hours. Since a finer grind leaves more surface area open to water, it will extract faster.Second, with a finer grind, you will probably get a bit more sediment that sneaks through the coarse metal filter and into the eventual brew. You can pour the concentrate through a paper filter or cheesecloth.We've recommended starting points for all of these variables (grind size, water temperature, steep time, dilution) to give you a great tasting cold brew - both using our cold brew mesh bags, and brewed in a French press. However, you should definitely experiment! Remember to adjust one variable at a time, or else you won't know which change worked or didn't work!