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Coffee extraction: how you can tell if you’re over or under extracting 

If you’re new to the fresh coffee game, you may not be familiar with the phrase ‘extraction’. While it sounds like something rather mechanical, it’s actually one of the most natural elements of the coffee brewing process. Extraction refers to the introduction of water into your ground coffee, whether that be within a french press, percolator or pull espresso machine, and its purpose is to extract as much coffee flavours as possible from the oils in your grounds. It turns water and grounds to your favourite cup of jo! 

Why bother thinking about extraction?

So, why think a little more deeply about the coffee extraction process? Well, to put it simply, it’s pretty much the biggest factor that influences how your coffee tastes beyond the actual bean variety itself. The way the flavours in your coffee grounds have been extracted influences the bitter oils released from the caffeine in your coffee, the level of acidity in your coffee (impacting the overall sweet or sour profiles) and whether your coffee ends up overly muddy, or excessively watery. If your coffee is under-extracted by not being given enough time to brew, having the wrong grind size, or the wrong temperature, you’ll likely end up with a watery mouthfeel that tastes highly sour and bitter, due to little time being given to the sweeter notes of the grounds being the last in line to release. Brew for too long and you’ll be left with a muddy over-extracted brew that is overpoweringly sweet or acidic. This might sound a tad overwhelming, but reaching the perfect balance of extraction isn’t too complicated; and it’s well worth knowing how to get the best out of your beans by preventing a bad extraction or troubleshooting one you’ve found yourself with. 

Preventing a bad extraction

When it comes to nailing the extraction level in your brewing process, there’s not a cut and dry solution. It’s entirely based on the beans you’re working with, and there are some factors, like whether you live in a hard or soft water area, that you don’t have lots of control over. There are, however, a few things to keep in mind from the off to try and get the best out of your beans. 

Firstly, think water temperature and quality. The hotter your water, the more quickly it will extract the oils from your coffee, and the colder, the more slowly. As with coffee ground coarseness, this can be used in your favour depending on the heat requirement of your beverage. You can alternate brewing methods and grind sizes to support the potential extraction speed if you think this could act as a stumbling block for great extraction. When it comes to water quality, this is all about how soft or hard the water is where you live. If you live in a hard water area, your water is more likely to contain additional mineral contaminants. While a small amount supports extraction, excess minerals can slow down the extraction process as your actual grounds have less opportunity to be affected by the water. You can work around this by utilising an espresso machine with a built in filter, or use a separate water filter beaker, which can be kept in the fridge. 

Next, think grind size. A finer grind is more likely to be over-extracted, and a coarser grind to be under-extracted, based on the surface area available for water to push through. If your beverage of choice has an advised coffee grind size, you can work with this knowledge to avoid extraction errors, by selecting a brewing method that avoids either side of the problem. A finely ground bean, for example, is more prone to over-extraction, so, if you can, choose a brewing method that is as fast acting as possible (like an AeroPress or espresso machine for example) to give your beans their best chance. Equally a coarser bean is more likely to be under-extracted, so opt for a long acting brewing method such as a percolator, drip method, or french press. 

Finally, if you’re going for a slow working method like drip, or pour over coffee, think about the surface area of the grounds that you’ve placed in your coffee filter. The thinner a surface area, the quicker the extraction, and vice versa. This comes into play most when brewing large quantities of coffee all at once, as it’s harder to get an even layer the more grounds you’re using. We’re working here largely on getting an even layer in order to ensure extraction is consistent, and working on smaller brew batches.

Troubleshooting a poorly extracted brew

Beyond getting the right factors in place to achieve a good extraction, your knowledge of the process can also troubleshoot a less than satisfactory brew. Once you’ve had your first sip of your coffee (and for some advice on what to look for in a good brew check this article out) look out for an excessively sweet brew or one that feels overly strong and muddy. This will likely mean you’ve over extracted your grounds; and you need to opt for a quicker brewing method, such as swapping your french press for an AeroPress or using an espresso machine, or higher temperatures when brewing. Alternatively you can choose a finer grind size to speed up the process with your preferred brewing method. On the flip side, if your brew is watery and bitter, there’s every chance you’ve under-extracted the grounds. In this case you’re better off opting for a slow brew method, such as a drip coffee or french press left for a decent amount of time; or going for a coarser grind to slow down the process and working at colder temperatures. You may find this also happens if you’re living in a particularly hard water area; in which case, follow the same advice. 

So, now you have an idea of what to look for in the extraction process, we hope you’re able to utilise your knowledge to get the best extraction from the off, or troubleshoot it if you find you’re coming across problems when getting to your long awaited cup of jo. As you can probably tell by this point, there isn’t a set rulebook on what to do for every bean, but having an idea of what factors can influence extraction mean you can work with your beans, brewing method and recipe, rather than against them.

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