Coffee Data Science

Brew Ratio for Espresso

Exploring output to input ratios

Robert McKeon Aloe
Towards Data Science

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Espresso brew ratio have a large range and a huge image on the mouthfeel of the taste and the intensity of the shot. Many stick with 2:1 (output to input) shots, and more recently, the idea of a long, slow shot at a 3:1 ratio or even 5:1 ratio has been popularized. I personally prefer a shot ratio between 1:1 and 1.4.

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For this short test, I wanted to show the difference in shot ratio and discuss the impact on taste. I think the variable is more personal than other espresso variables because of the effect on mouthfeel. I’ll specifically look at the ratios 1.5, 1.3, and 1.1.

Acknowledgement: many people write brew ratios as input to output, but I prefer the other way because I prefer to have the larger number of a ratio on the left side of a ratio colon.

Shots in Pictures

For these shots, I used a Rok grinder, a Kim Express machine, a VST basket, an Pyxis scale, and a home made distributor. Each shot is staccato tamped with a longer pre-infusion than normal (at least 30 seconds), and I use pressure pulsing during infuse. All three shots are only different in brew ratio.

I considered making a salami shot so I could taste the same shot exactly, but there is a big impact on initial taste, mouthfeel, and aftertaste that could be confused compared to using three separate shots with long intervals between each shot. In that regard, I hadn’t eaten anything or drank anything before these shots, and they were all pulled a few hours apart.

Each column is a different brew ratio at a few different times during the shot:

1.5 : 1 …………… 1.3 : 1 ……………… 1.1 : 1

All three shots had similar extractions, which was a good sanity check. They also looked similar at the same time intervals.

Metrics of Performance

I use two metrics for evaluating the differences between techniques: Final Score and Coffee Extraction.

Final score is the average of a scorecard of 7 metrics (Sharp, Rich, Syrup, Sweet, Sour, Bitter, and Aftertaste). These scores were subjective, of course, but they were calibrated to my tastes and helped me improve my shots. There is some variation in the scores. My aim was to be consistent for each metric, but some times the granularity was difficult.

Total Dissolved Solids (TDS) is measured using a refractometer, and this number combined with the output weight of the shot and the input weight of the coffee is used to determine the percentage of coffee extracted into the cup, called Extraction Yield (EY).

Performance

Taste improved for a shorter shot. This is no surprise for me because there isn’t much left to extract after the 1:1 shot. As the TDS increases, the mouthfeel really improves. Too short of a shot can end up being too sour, but I didn’t find this issue for this roast in particular.

Shot ratio

Pre-infusion went a few seconds longer for the 1.5:1 shot, but overall, the times were very similar.

TCF is Time to Cover the Filter

Some times we get so locked into a certain parameter that it is hard to experiment. The best way to experiment for shot ratio is to make a salami shot (using multiple cups) so that you can taste the different parts of the extraction and mix them together.

My aim isn’t to tell everyone to pull a certain shot ratio (in this case, a lower shot ratio), but rather, my aim is to encourage experimentation.

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