The espresso re-extraction experiment

The Espresso Re-extraction Experiment

Over the past year I spent quite a lot of time thinking (and writing) about carbon dioxide and its role in espresso extraction. At the end of my last blog post, I wondered if “re-charging” stale coffee with carbon dioxide could make it pour like fresh coffee.

Over the weekend I did a little experiment to test exactly that. The result was so astounding that I repeated it again the following day, this time on video!

The experiment?

Some time last year I was given a bag of pre-ground coffee by a friend. Now, I was never going to subject myself to drinking it, but it was perfect for this experiment.

This stale pre-ground coffee was perfect for experimenting – but I wouldn’t drink it!

I pulled two shots from a single dose of the pre-ground coffee. The first shot was as you might expect – it ran fast and was dark, thin and had no crema. Without the benefit of flow control, it would have been messy…

Next, I added a small amount of bicarbonate of soda (aka bi-carb / sodium bicarbonate / baking soda) to the spent puck and extracted it again. If you’ve ever tried re-extracting a spent puck, you’d probably expect it to run really fast, with lots of channeling and generally make a big mess. But, low and behold, a thick syrupy pour with a lighter caramel colour and even some crema!

It still smelled stale and nasty, but it poured almost like fresh coffee; worlds apart from the first shot! This is despite being at least 8 months old, pre-ground and unsealed for the past week!

Note: I am not suggesting that adding bicarb soda to stale coffee will somehow improve it. This experiment was simply to explore the influence of carbon dioxide on the flow of espresso.

The outcome leads to more questions:

  • is degassing the reason for the established wisdom that tells us to grind immediately before use?
  • is degassing the primary variable driving the need for grinder adjustment?
  • if so, could a source of variability be removed by storing roasted beans in a pressurised CO2 rich environment?

Anyway, here’s the video:

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