Title credit to Malice from Clipse with the lyric from their hit Grindin'
Nothing sets up a deep dive into coffee science quite like an early 2000s hip-hop reference, but here we go!
Is there anything better than the waft of aroma that immediately follows the grinding of coffee? Full disclosure – every time I grind at home my first move is diving in for a deep inhale over the grounds to relish the sweet-smelling symphony of scintillating scents (alliteration bonus +5 points). There are over 800 aromatic compounds in roasted coffee which are all released upon grinding, covering every aspect of our perception of smells. A scientific study even found that this combination of aromas can actually relieve stress and have an antioxidant effect on the brain.
Grinding coffee at home is not only about aroma of course, and the way in which it is done along with the timing of that grind have a major impact on how your coffee tastes. In the last blog, (Did I brew my coffee right?) I briefly touched on the topic of grinding coffee, noting that not only timing of the grind but the consistency of the grind make a big difference when it comes to extracting the optimal flavor. Here I want to dive deeper into the grinding process in terms of equipment, take a look at what we mean by grind consistency, and critically assess the impact of timing.
For hundreds of years before the invention of the coffee filter, coffee was pulverized – literally pulverized with stone – either with grain mills, or mortar and pestle (pictured above is the mortar and pestle that made its way to America on the Mayflower) into a powder so fine that it would all be dissolved into the finished product. The man deemed ‘the father of the English coffee house’ wrote in 1634 of an experience drinking coffee in Egypt that was “…made of a Berry as big as a small Bean, dried in a Furnace, and beat to Pouder, of a Soot-colour, in taste a little bitterish…” This passage is one of the earliest writings about how coffee was prepared.
Luckily today none of us should have to ‘beat’ any of our coffee to powder as coffee grinders are fairly easy to come by. While I will detail below more specifically why the grind is so important, the main thing to keep in mind is that the grind is your first chance to influence the amount of flavor (often described as solubles) that is extracted during the brewing process. General rule of thumb is that a fine grind yields more solubles and a coarser grind yields less which means that there is a somewhat inverse relationship between your grind size and your brewing ratio to achieve the desired extraction.
Complicated science words aside, there is a logistical hurdle we have to get over and that is that other than whole beans and the coffee ‘pouder’ [English spellings are always weird to look at but also make way more sense if you really think about them] there is NO method of grinding that is 100% consistent. Whole beans are 100% whole and superfine powder is also 100% superfine. The reality is that every grind – even those done on professional equipment – are some combination of very fine particles and somewhat larger particles. So the goal for anyone trying to make coffee at home is to try and control the ratio of fine to large particles as best they can so that there is less variation from grind to grind and within their grind i.e. consistency. More consistency in your grind = more even and predictable extraction so that the grind part of the coffee equation is far less of a variable impact on flavor. To assess consistency, let’s look at a few common home grinding methods.
The most common type of home grinder is a blade grinder which essentially functions like a food processor. If you have ever used a food processor, you can very easily translate their shortcomings to those of a blade grinder. They are great for very rough chops, and for very fine minces, but there is very little middle ground. A blade grinder will almost always result in an inconsistent outcome and will vary largely depending on who runs the grinder and for how long. We would not recommend using this type of grinder, but it will work better than beating it into a powder!
If you are still reading this blog 700 words in, you have probably heard about burr grinders already. The most common of those at home is a conical burr grinder which you can find from a number of different manufacturers and range in price from $40 to well over $500. Rather than chop beans like the blade grinder, the burrs use gravity to feed the beans through a pair of burrs that crush the beans and only allow particles of a certain size to fall through into the collection container. I have my own recommendations for the best home grinders, so please feel free to DM us in Instagram @quartetcoffee or shoot as an email at firstname.lastname@example.org and I will gladly share those, but the truth is that any burr grinder will be an upgrade from a blade grinder. The other truth that I have learned over the years is that whether you spend $40 or $500 on your home grinder, you will never come close to the consistency of a commercial grinder.
Below are two pictures that illustrate the difference between a relatively high-end home grinder, and the commercial grinder we use in our shop:
The goal of your grinder is to crush the beans into particles that are very similar in size so that the extraction is even across the entire brew. Even extraction allows predictability which in turn provides you, the brewer, with a better sense of the proper brewing ratio. This is no different than a recipe that calls for something like the ‘juice of one lemon’ – depending on the size of your lemon, the flavor that comes through in your dish could vary wildly.
Both pictures above contain our natural processed Brazilian coffee, roasted to Full City and ground for pourover use. The coffee in the first picture was ground using our Ditting KR1203 grinder which we use in the shop, while the coffee in the second picture was ground using my personal home grinder the Baratza Encore. You may notice the differences in these pictures already, but below I added some crude drawings to highlight the larger pieces that remain:
The grinds from the Ditting have remarkable consistency, such that there were very few ‘fines’ (i.e. very fine particles) and the largest pieces are barely greater than the average size. By contrast, the grinds from the Baratza Encore have noticeably finer fines and larger outliers from the average size of the grinds themselves. This is not to say that the latter is necessarily bad it just means that the inconsistent grind size will mean adjustments need to be made to the ratio to achieve the optimal level of extraction.
When to Grind
You might think this section will be pretty short because you probably already know what I will say – grind immediately before you brew – but I think the why behind the what is always just as important. People have asked about coffee storage and the answer I always give are that there are two enemies to coffee: light and oxygen – such that any storage solution must keep as much of those two things out as possible. We will talk about light at a different time, but for now our focus will be on the air we breathe.
After roasting, the off-gassing of CO2 from the whole beans creates a sort of protective layer around the beans themselves, insulating them from oxygen. [Science side note – this is about volume and density as CO2 is heavier than Oxygen so CO2 stays close to the bean and Oxygen will sit on top of that like a cloud] Staving off oxygen is incredibly important because it is contact with Oxygen that leads to… OXIDATION (dun dun dunnnnnnn)
According to experts at Handground.com “oxidation is the process of oxygen pulling away electrons from another molecule. These molecules, with an uneven number of electrons, become unstable and begin reacting with other molecules around them. Called free radicals, these volatile compounds are the root cause of browning, aging, rusting, and in the coffee world, staling.” Obviously, the more surface area with which the oxygen has contact, the more reactions can take place and the quicker staling will occur. Whole-bean coffee has far less surface are than ground coffee. The SCAA (specialty coffee association of America) even built this handy chart to demonstrate what we all clearly know:
Clearly, grinding into smaller pieces leads to more surface area which then leads to more chance for oxidation.
The grinding process is probably the aspect of coffee brewing at home over which you have the most control. If there was one thing to focus on perfecting in your home setup I would highly recommend upgrading to a burr grinder. This will take so much guesswork out of your coffee process, and allow you to have a more standard floor for comparison as you try new roasts. Once you have done that, make sure you grind right before your roast. The only caveat would be on coffees that were roasted within the past few days – for those grind them and then let them rest for 15-20 minutes to let them settle down a bit and complete the off-gassing of CO2. If you are curious about grinders or brewing techniques, or any sort of intense coffee stuff, don’t hesitate to reach out to us!