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The Coffee Sneeze in Espresso

Fines at the Start of an Espresso Shot

I noticed something in my espresso videos recently as I have been pulling more staccato shots. It seemed like steam or something was blowing in front of the camera for a split second at the very beginning of the shot. I investigated because I was worried about a leak in my machine, and I found out it wasn’t steam; it was coffee.

When pressure was first applied during pre-infusion, a small flurry of fine coffee blew into the cup.

Before and after the start of Pre-infusion. All images by author

Let’s zoom in on the bottom of the cup.

This tiny bit of evidence shows the air pushed out from the top of the puck forces a small amount of coffee out.

So I wanted to measure the total amount coming out with a quick experiment:

Less than 0.01g of coffee came out. It was not detectable with my Acaia Pyxis scale.

This coffee sneeze happens for staccato shots frequently, at least with a lever machine like the Kim Express where the pressure goes from zero to 2 bars almost instantly. This doesn’t happen as much for regular shots (non-staccato), or it is harder to see. However, I’m curious how the air being pushed through grounds affects the distribution inside the puck.




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Robert McKeon Aloe

Robert McKeon Aloe

I’m in love with my Wife, my Kids, Espresso, Data Science, tomatoes, cooking, engineering, talking, family, Paris, and Italy, not necessarily in that order.

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