Flavour stability of filter coffee

We've all been there, sat in a pub, had a great lunch / dinner and then ordered a filter coffee only to find that it tastes as bitter as hell and smells burnt.

Who's at fault here, the pub or the coffee roaster?

Well we've put our filter coffee to the test, we brewed 60g of Kenya and Colombian coffee with about 1.5 litres of water in a Bravilor Mondo 2 filter coffee machine. We then tasted the coffee every 15 minutes to see how the flavour of the beverage held up.

1. Freshly brewed - Pleasant light taste, the brightness of the Kenya shining through

2. After 15 minutes - No discernible change in the coffee flavour

3. After 30 minutes - Some of the bright notes starting to get lost. A slightly heavier coffee taste is coming through. Still quite drinkable

4. After 45 minutes - The darker notes are starting to become more prominent, however still drinkable and a good colour when milk is added.

5. After 60 minutes - Hint of a smoky flavour coming through, the lightness of the original brew has now gone, however still an acceptable beverage and retaining a good colour when milk is added.

6. After 85 minutes - Smoky taste becoming more pronounced, still drinkable and still looking fine when milk is added.

7. After 100 minutes - A very discernible burnt taste is now coming through to back up the aromatic change. Surprisingly the colour when milk is added remains good, and the milk (particularly Jersey Yellow) masks and lot of the damage.

8. After 115 minutes - Not much change to the last commentary

9. After 175 minutes - A caramel burnt flavour has now appeared.

The time-scale we used for our test would be typical for an outlet on a quiet day and highlights how important it is to be aware of demand in a food service environment. It's very easy to get a reputation for inconsistent drinks and drive customers away.

My final comment would be a pat on the back to Bravilor whose machine we used. The hot plate although gradually stewing the coffee was doing so at a much slower rate than I thought it might. The engineers have clearly got their holding temperatures set about right which is pleasing to us roasters.