DID YOU KNOW THAT COFFEE NEEDS TO "REST" AFTER BEING ROASTED?
HOW LONG SHOULD I AGE MY COFFEE BEFORE DRINKING IT?
- Coffee in standard packaging (i.e. not gas-flushed) is better to drink within 1-3 weeks from roast (ideally around 1.5 weeks).
- Coffee in gas-flushed packaging is at its prime after 2 weeks of shelf time.
COFFEE FRESHNESS BY PACKING METHOD
HOW DID WE DETERMINE THIS?
First things first: What is Ageing?
Ageing refers to the development of coffee flavours over time, typically with a positive connotation. Staling refers to the same thing with a negative connotation. Whether you refer to the development as staling or ageing, detectable taste changes occur in roasted coffee over time.
Changes to a coffee taste result from two different natural phenomena:
- Chemical transportation
- Chemical transformation
It’s a complex business. The complexity is further increased when you take into varying account coffee origins, roast degree, water activity (pre- and post-roast) and atmospheric conditions. Accounting for every mechanism and variable that changes taste is difficult – although we’re working on it! In the meantime, we have done some simplified studies around the ideal time post-roast to enjoy your coffee.
WHAT DID WE DO? (HOW DID WE TEST THIS?)
We planned our experiments to observe quantifiable and qualitative changes to three different coffees over time: a light roast blend, a medium roast blend, and a dark roast blend. These coffees were all roasted on the same day with the same environmental background conditions. We observed the difference between gas flushed** (2 parts per hundred [pph] oxygen) and non-gas-flushed products (21pph). The coffees were tasted at increments of 1,2,4, and 8 weeks of shelf life.
(** – gas flushing refers to the process of adding nitrogen during packing to delay oxidation and extend shelf life)
- We tested the coffees with five trained coffee tasters (including a certified Q-grader).
- We took into account palate variability and recorded this in our results (i.e. differences in perceived quality).
- We scored the coffees out of 5 in the categories of sweetness, mouthfeel, milk cut-through (yes, we tested in both milk and black), and balance.
- We also mapped the observed flavour of the coffees over time.
- Ambient temperature was not monitored or controlled in this study (Phase 2 will look at this) – however, our storeroom temp is typically in the range of 18C – 26C
- Other factors that were not controlled in this test were relative humidity during roasting, holdup time in packing and ambient pressure (Phase 2)
As we all know, results from scientific work are relative. Numbers mean nothing unless there is a standardised reference point on which to compare them. So which standard do we use the calibrate our taste buds? Well, in this study, we didn’t know which roast ‘shelf life’ was appropriate for a standard across the weeks of testing (though we do now! – begin phase II!). So, we reported our results as flushed vs. non-flushed. In other words, we tracked the quality of non-flushed coffee as it improved and deteriorated relative to gas-flushed coffee. We didn’t assume the gas-flushed was a constant; reactions still occur under these conditions. However, what was important to observe was where the ideal quality crossover point existed (i.e. when gas-flushed became superior to non-flushed), and when the coffees no longer became acceptable to drink.
WHAT DID WE FIND?
We found that non-flushed coffee is much better drunk within 3 weeks post-roast (ideally around 1.5 weeks). We also found that gas-flushed coffees are at their prime after 2 weeks of shelf time.
We have summarised the results in a normalised score vs. weeks post-roast in the figure below.
CONCLUSION
At this stage, we can confidently say that if your coffee is not gas-flushed, drink it within 3 weeks! If your coffee is older than this, all is not lost: the coffee is still drinkable black for up to 8 weeks. This is true for light, medium and dark coffees.`
If your coffee is gas flushed, your coffee will stay fresh for over 8 weeks. At no point did the quality decrease over the tested timeframe – in fact, it only ever increased (if only slightly), indicating that the coffee is likely to be good for longer than this. Milk cut-through is good throughout its lifetime, though if you want to serve it black, we recommend waiting until after 2 weeks.
For reference, most of our blends are nitrogen gas-flushed at our roastery – with some exceptions.
About the Author:
PhD, B.E. (Chemical Engineering) Adam of the Coffee Science and Education Centre (CSEC) has worked in research for over 8 years, with an overarching focus on high-temperature water technology. He has worked in Australia at the University of New South Wales, and internationally at Cornell University, the Massachusetts Institute of Technology and Aerodyne Research Inc. The applications for his research have been diverse, including advanced particle production technologies, reaction engineering, sustainable fuels processing and novel extraction technologies. Once he discovered the application of his experience to the coffee industry, there was no going back! Adam returned to Australia in 2015 to pursue his interest in designing his own coffee technologies. He created the startup Highpresso PTY LTD to provide research consulting services to the coffee industry and build new coffee technologies. His research led him to design a new roasting system that prevented the charring of raw beans. Now, Adam uses his skills and deep love of coffee to improve the understanding of coffee science and technology. He designs experiments around testing the latest and greatest coffee gear available to the industry and uses his connections to develop research projects centring around brewing better coffee.