Referencing my previous reflections on coffee freshness and particle size distribution, I have determined the best practice to make pre-ground coffee stay as fresh-tasting as possible is to sift, vacuum and flush it with nitrogen before sealing it in an air tight container. But what if I am wrong? What difference does it make if I forego any of the above steps? I decide to do a little sensory evaluation on ground coffee under different storage condition.
In my previous research and experiment during the conception of COFFEE IN A POUCH, I’ve already concluded that for long term storage, it’s best to reduce the amount of the extreme fines in ground coffee. In comparison, I noticed the water passed through the ground coffee sample without fine reduction much slower than the sample with a reduced amount of fines.
In this simple taste comparison, samples are the same batch of coffee, all sifted to reduce the presence of extreme fines. The first sample is then vacuumed, flushed with nitrogen before sealing in an airtight pouch. The second sample is also vacuumed but sealed immediately afterwards. The third sample is vacuumed (so it went through the same VOC displacement as other samples) but not sealed at all.
This coffee is roasted on 1/18/2022, processed on 1/31/2022. The taste evaluation is conducted on 5/15/2022.
The first part of this evaluation is for immersion brewing environment.
Particle size distribution: under 400μm is 0.4g, between 400μm and 800μm is 2.65g, between 800μm and 1000μm is 9.95g
The TDS on all three samples are identical. The result between the first and second sample is in fact quite similar. However, the first sample does exhibit more defined tasting notes. I was able to pick out peach and other nuances in the brew. The second sample showed a higher level of acidity, but is comparatively less balanced and complex.
The third sample smelled slightly rancid upon assessment. And it is also the far inferior brew of the three.
The second part of this evaluation is for percolated method.
Particle size distribution: under 400μm is 0.4g, between 400μm and 800μm is 2.05g, between 800μm and 1000μm is 11.15g
With a coarser grind setting. The first and second samples showed a more vibrant aroma with more floral and fruit forward attributes. The TDS on the first sample is 1.5%, brew time is 3’26”. The TDS on the second sample is 1.2%, brew time is 2’52”. Brew quality between the first and second is yet again very similar. The first sample again showed a more defined flavor profile. I could taste lime grind vividly where the second sample showed a sharper acidity and was over all more muted.
The TDS of the third sample is 2%, brew time is 2’45”. Stale aroma and the cup quality is significantly worse.
After this quick experiment, I was pleased to know my current practice regarding COFFEE IN A POUCH and POUROVER IN A POUCH does result in a higher cup quality than other potential workflow. A little context here is that during the conception of Halfway There Coffee, I already did multiple experiments on this matter. So it’s not like I just blindly started this process without accessing the corresponding result. But it’s still nice to know that I haven’t strayed.
That being said, in today’s evaluation, I did not conduct multiple samples to obtain a less incidental data. So the result of this experiment should only serve as a reference rather than a scientific conclusion.
I do find it interesting to know that even after months, the slightly coarser grind showed more presence of VOCs. One other thing is I’ve always known COFFEE IN A POUCH produces more consistent results. But I was not expecting the TDS to be identical. But after all, one should not obsess over TDS too much as it tells us very little about the content of its reading.
How to store pre-ground coffee at home?
There are some chemicals in the roasted coffee that react to oxygen and turn into a different chemical that we attribute to the coffee tasting stale. Heat also accelerate that process. That's why when it comes to coffee storage, especially pre-ground coffee, airtight and storing in a cool place away from light source are generally a good direction.
Gas displacement is comparatively more difficult to achieve in a home setting. But there are ways to reduce the oxygen level of your coffee storage at home.
For a vacuum method, Fellow Products has a Atmos Vaccum Canister that can reduce the oxygen level in the jar. I personally recommend placing a piece of coffee filter on top of the ground coffee before sealing.
This canister creates vacuum by ejecting small amount of air out of the jar every time you "twist" the lid. There is a pressure indicator on the lid that sinks in whenever a pressurized environment has been created (like an instant pot).
For a nitrogen flush method, you can utilize a whipped cream dispenser. Make sure the dispenser is clean, dry and free of odor before use. Place a piece of coffee filter over pre-ground coffee. Aiming the dispenser at the filter and flush your air tight container with nitrogen before quickly closing the container.
This method is not perfect. The execution can get a little messy and it may take you couple times of practice to get the hang of it.
Pre-ground in small batches
Pre-grinding coffee may lose some of its precious chemicals and accelerate the natural phenomenon of flavor deuteriation. Grinding breaks down whole beans into significantly smaller particles, therefore increasing surface area, making it much easier for gas to escape and for oxidation to take place at a faster pace.
However, for general coffee consumption, you can still achieve a very decent cup quality within 4 to 6 days after grinding. So when you do have to pre-grind your coffee. as long as you do so in small batches, allowing you to consume the coffee within a short period of time, and making sure you keep the container in a cool and dark place away from light source, you can still enjoy a good quality coffee.
As a matter of fact, the quality of the coffee itself and ground quality might play a bigger role in pre-ground coffee preparation. Utilize your local roaster where you get your coffee from. Some coffee roasters even provide pre-ground option for online orders. However, I will still recommend not grinding any smaller than you would for an aeropress setting.
I will also recommend leaving your coffee 7~10 days to "rest" after the roast date before grinding. This ensures you have a more even consistency of your coffee ground. It also give the "roasty"-tasting compounds a chance to dissipate.