Resting Coffee

Coffee is a very hydroscopic product. Exposed to air it will degrade quickly. After a few days its flavour will alter negatively due to a combination of moisture and oxygen from the air. Coffee releases CO2 formed during roasting and trapped inside the bean. This CO2 also negatively affects the flavour and it is recommended to “degas” for at least 7 days. Degassing involves letting freshly roasted coffee beans to rest in a controlled environment. This allows CO2 created during roasting to escape the beans instead of ending up in your cup.

The enzymatic action in coffee, especially in certain natural (cherry/dry) processed coffee, continues well after roasting and some of these coffees become much nicer with time after roasting. A lot of coffees become more balanced 2 -3 weeks after roasting. Some highly priced natural Geisha coffees reach their peak flavour after a couple of months, provided they are shielded from moisture and oxygen.

Hence, it is very simple, coffee needs to be rested for at least a week and packaged in high barrier packaging soon after roasting. Once the packaging is opened deterioration will accelerate.

Coffee Valve – Explained

The coffee needs to be shielded from moisture and oxygen immediately after roasting and at the same time it needs to be allowed to get rid of the CO2.  That is why coffee bags have a one-way valve installed: to let the CO2 escape. You can also get a whiff of the coffee smell through the valve although the smell exuded by beans might not at all reveal the true character of the coffee. 

This little valve has a little membrane (something similar as the one-way valve in inflatable beds etc.) that only allows gas out and not gas in. A little marvel of technology.

Have you ever had a puffed-up bag of coffee? That is probably because the one-way valve was not working well. We also experimented with not putting in a valve at all and letting the coffee degas in silos for 10 days. Even then the coffee bags would puff up. The volume of CO2 released after roasting is over 2 times the volume of coffee or up to 1.5% of the weight (CO2 in coffee)

Layers of Coffee Packaging

Good coffee bags are relatively complex.  Coffee packaging, historically and still, mostly consists of 3 layers. An outer layer that provides a good printing base or other aesthetic properties (and a minor barrier) and that protects the middle layer. The middle layer is usually a thin, expensive, high-quality film with good barriers for both oxygen and moisture. The middle layer was traditionally made of aluminum foil and nowadays mostly of a metalised film. The inner layer allows the bag to be sealed and provides mechanical structure, like stiffness, to the bag, and it protects the middle layer. It also provides a decent barrier to moisture.

On top of that a pinhole is made in the bag and the one-way valve is heat- sealed over this hole. 

The layers of film are laminated together with some sort of very efficient adhesive.  All these materials are certified for contact with food.

The Importance of Quality Materials

Once coffee is packed in very high barrier packaging it stays good for up to 2 years. The flavour degrades only very slowly when stored in a stable, cool temperature out of UV light. Enzymatic action, aroma escape and oils degradation slowly continue and will reduce the flavour of coffee but it is a slow process provided there are good barriers. The quality of the one-way valves is very important as the valve will become the weak link and in time it stops working properly and let moisture and oxygen in. There are only a few trustworthy sources in the world for quality valves.  Also when bags are formed from laminate film, tiny pinholes or rips may occur in the middle layer due to the folding and heat application during bag forming, affecting the quality of the barrier. This was a shortcoming of aluminum foil as inner layer – it is brittle and susceptible to little holes whilst the outer and inner layer remained intact.

No plastic is entirely impermeable to oxygen but there are big differences. This is where selection of very good barrier materials makes a huge difference and for example the paper bags with some polypropylene layer hardly gives any protection and the coffee starts to degrade immediately. Unfortunately, it is impossible to get compostable packaging that can match the best plastic packaging and a compromise has to be found.

The selection of film is quite a process. Apart from the barriers you need to be able to make bags from it without ripping or tearing, they need to stand up and you need to be able to seal them with heat. Some materials, especially the compostable plastics only seal in a narrow temperature range. Quite a few forces are acting on the material when the bags are formed which might lead to tearing of the bag. That is why there is reasonable large empty space in the top of coffee bags.

Modified atmosphere packaging (MAP)

The air around us contains moisture, 21.9% oxygen and airborne spores. When coffee bags get sealed there is air in voids around the coffee and mostly in the top of the bag. Although not a lot, this air will still interact with the coffee and that is why we purge the bags before filling with dry nitrogen, an inert gas that is the other 78% of air that we breath. More importantly that is why we package the coffee within a minute of grinding. Ground coffee has a surface area hundreds times bigger than beans. Immediately after grinding the grounds will release some CO2 but thereafter the absorption of oxygen and moisture starts. It is paramount that the grinds get quickly packaged in preferably a nitrogen flushed bag with good barriers and seals.

Buying in bulk

Buying your coffee in bulk containers like some other bulk foods might work for some people but the problem with bulk food containers is that they are not airtight and coffee degradation is rapid. That then requires more frequent trips to the shop and in most cases accepting a lower quality product compared to its packed equivalent.

At IncaFé, we specialise in organic specialty coffee, which we import directly from growers, mostly in Peru. Peru is ideally suited for specialty coffee with much organic rich soils at high altitude and good rainfall. Check out our range of organic coffee to learn more.