Why doesn’t coffee last forever?
Maybe far in the space age future, there will be a coffee product that will always taste the same. But for now, we will have to talk about coffee brewing in the 21st century. There are about 1000 different chemical compounds identified in coffee. Coffee brewing as we know it, is to extract a balanced amour of those compounds, not too little, not too much, into the cup. But what if some of these chemical only exist for a certain amount of time? What is some of them changes? Is there anyway to preserve coffee at its peak, forever?
About the flavors of coffee
Luscious coffee trees produce lots of white tiny blossoms that look like scattered starlight caught by the branches. It is said that the flowers have a strong scent that reminds people of jasmine. Coffee blossoms then bear coffee cherries which can take up to about 9 months to fully ripen. Environmental factors, genetic factors and agricultural practices will all impact the quality of coffee.
Coffee is a labor intensive crop to harvest. Because it’s very common for a single tree, even a single branch to show different stages of fruit bearing, only by handpicking can you make sure only the ripe ones are picked. After the the harvest, cherries need to be processed. After the pulp is removed, the seeds exposed and dried, the green coffee travels, oftentimes across the world, to your local roasters. Green coffee at this stage shows very little trait to the beverage that we enjoy so much. Only by roasting meticulously can one unlock the explosion of flavors, it is then the coffee beans that we know, small but mighty, and come a long way.
But like all great beauty in the world, it fades. Once roasting is completed, a multitude of physical and chemical processes immediately start.*
The lost of freshness in coffee can be summed up into 3 scenarios:
1. Volatilazation
Aroma is a very important part when we talk about sensory molecular science. It’s a big part of how we enjoy our coffee. The extremely sensitive volatile chemical compounds that reminds us of blooming flowers, spices and refreshing fruit are the most noticeable when coffee has been store improperly or too long. The only way to guard the lost of volatile compounds is impermeable package.
2. Intrinsic reactivity
After roasting, some of the chemical continue to react to other compounds in coffee. That’s why it’s an effective method to access the evolution of aroma profile of a coffee to determine if it’s still fresh. This is unavoidable. But study has shown that lower temperature can help slow down this phenomena.
3. Oxidation
The exhilarating fresh coffee aroma fades, and new volatiles with off-notes are created*. The obvious solution is to reduce/eliminate the presence of oxygen by vacuuming or replacing the air in storage environment with inert gas.
Coffee won’t stay fresh forever. But by exercising caution, it is still possible to experience a fresh tasting cup even months later. Packaging material with effective barrier quality can help against the loss of volatile compounds. Storing coffee in a cool and dark place can slow down the natural flavor degradation of roasted coffee. Replacing the ambient air with inert gas such as nitrogen can further reduce flavor loss due to oxidation. According to a study by Alves and others (2001), nitrogen-flushed coffee had a six-month shelf life based on sensory analysis, as opposed to coffee bagged with no flushing, which had a three month shelf life.**
A side note, during the inception of IN A POUCH series, I quickly found out that there’s another issue with sealing your coffee away. A vacuum environment may ensure a minimum oxidation of the bean. But the act of vacuuming itself may dislocate the precious volatile compound we are trying to preserve in the first place, especially when it comes to ground coffee.
Furthermore, a vacuum environment is a pressurized environment. It’s observed that upon depressurization, i.e. opening the bag, it creates an accelerated degradation of flavor.
Currently, for our IN A POUCH production, there’s a strict 10 minute packaging process: coffee is ground and then transfer to a sifter, which it will sift the coffee ground for 2 minutes. The agitation creates lots of lost of VOCs at this stage, but the resulted ground with much narrower particle distribution outweigh the loss.
Next, coffee ground is measured and packaged. Pouches are vacuumed for 0.3 seconds. This very specific set up makes sure it sucks out most ambient air but not vacuuming the pouch entirely. It’s then flushed with nitrogen and securing sealed off in a PLA lined kraft pouch.
I found this to be the most effective method to preserve freshness in my limited facility.
* Chahan Yeretzian, Imre Blank, Yves Wyser “Protecting the Flavors-Freshness as a Key to Quality”
** Emma Safe “What is the Shelf Life of Roasted Coffee? A Literature Review on Coffee Staling”