Grinding Coffee Beans for Cold Brew
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All coffee will taste better if the beans are ground right before use. When coffee beans are ground, the coffee oils inside them are exposed to oxygen, which causes them to quickly oxidize. Coffee made with oxidized oils will taste stale.
This process of oxidation starts within 15-20 minutes of grinding. Flavor and aroma will deteriorate over time.
With such a wide range of coffee grinders in all price points, if you are serious about your coffee, you should seriously consider grinding it fresh before each use.
Types of Grinds and When to Use Them
The purpose of grinding coffee is to increase the surface area that comes into contact with water, which makes the extraction process more efficient.
As shown in the graphic, each brewing method requires a specific level of grind.
Coarse grinds have a consistency similar to kosher salt, while the finest grinds resemble powder.
There is a relationship between the degree of grind and the brewing time.
Finer grinds require less brewing time. However, if a fine grind is brewed for too long, it can lead to overextraction and result in bitter-tasting coffee.
On the other hand, since cold brew requires hours of water contact with the coffee, it is recommended to use a medium to coarse grind.
Two types of grinders—blade and burr
Blade grinders are inexpensive are also called spice grinders. They have a spinning blade (like a simple food processor) that chops the beans into fine bits. The longer you run it, the more finely the coffee is ground.
Note: Blade grinders can be used for both purposes but I recommend having one dedicated for coffee and the other for spices.
There are two potential problems with the blade grinder:
The most important is that grinds can have uneven particle sizes. This can lead to subpar flavor as some the coarse bits may get underextracted while the fine bits get overextracted.
When dealing with the long extraction times in cold brews, this flaw may be more apparent.
The second problem with the blade grinder is that when attempting a fine grind, the coffee may heat up, causing some of the flavorful coffee oils to evaporate.
Burr grinders work by crushing the beans between two surfaces. This creates a more even particle size than blade grinders.
There are disc and conical shaped burr grinders.
Disc grinders have a flat grinding surface, which could be better for finer grinds.
Conical burr grinders have cone shaped burrs.
Both have one stationary plate and one rotating plate. The disc grinders tend to rotate a little faster, which can generate some frictional heat.
With small batches, this may be insignificant. In both types, size of the grind is controlled by adjusting the distance between the two plates.
Conical burr grinders are considered the best choice as they rotate slower and a less likely to clog than disc grinders. Conical burr grinders are also the most expensive type of grinder.
For the home user grinding single use amounts of coffee, a disc grinder may be perfectly acceptable and save you some money. If you are an exclusive cold brew drinker however, consider that to make a concentrate you need a lot of coffee so you will not be grinding in small batches.
Burr grinders are the weapon of choice for cold brew aficionados. Their design allows them to produce a more even, coarse grind when compared to blade grinders.
For cold brew, we want a coarser grind to compensate for the extended brewing time (up to 24 hours). This will prevent bitter flavors as a result of overextraction.
To see my top picks for grinders, click here.
Can I Please Just Use Ground Coffee?
Of course! Sometimes it’s just more convenient. Or, perhaps you get up early and don’t want to disturb your household with the sounds of a grinder.
Some coffee brands will label their coffee with a roast date. Try to buy coffee that has been roasted within the past 6-8 weeks.
When you buy pre-ground coffee at the store or local roaster, it is usually packaged to protect the coffee from oxygen. After opening, you should use it within 2-4 weeks and each time you take some coffee out, squeeze the air out as you close it back up.
You can also buy airtight canisters to store your coffee in. A plus of doing this is you could grind your coffee during waking hours and then store it for use over the next day or two.
