What were we trying to achieve?

The goal of this test was learning whether the ONA Coffee Distributor (OCD) tool produces more consistent espresso than ‘palm tapping’ or ‘collapsing’ for not only experienced, but also inexperienced baristas. The initial concern with palm tapping was that it can be done in various ways depending on the barista’s experience, attention to detail and also how busy they are during service. So, we had two test subjects: an Experienced Barista, with many years experience preparing coffee and using various barista tools and equipment and an Inexperienced Barista, with little to no experience preparing coffee.

Before the experiment was conducted, the our hypothesis was that an experienced, detail-oriented barista may have high consistency with palm tapping and also with the OCD and that an in-experienced barista would have inconsistency with palm tapping and potentially more consistency with the OCD tool.

How did we go about it?

To find the answer to this question we needed to understand specifically what we were measuring and how we assess espresso extraction consistency. Furthermore, we had to understand the potential variances that could take place and how we could make distribution the only variable that would influence the results – so, we had to eliminate variance in other variables such as tamping, recipe, grinder variance and or how hard the handle is locked in.

Our main concern was that the variance in tamping between the experienced and non-experienced barista would create inconsistency, so we introduced a self- levelling tamper with a scale to ensure tamping was done consistently each time. This tamping was only done by the experienced barista and the only difference between test subjects was the distribution and palm tapping, not other variables.

The next thing we had to consider was “What exactly do we measure and how do we minimise bias in evaluation?” Firstly, let’s understand the key factors to espresso consistency starting with TDS (total dissolved solids). The shots were run alternating between palm tapping then OCD and back to palm tapping to ensure the grinder temperature, room temperature and also degassing didn’t come into play as a variable.

All shots were run to time 10 seconds after each shot was run, the same procedure was used to remove the handle, purge 3 seconds, and grind took place. For the inexperienced barista, the distribution method was conducted, then the handle was given to the experienced barista to tamp, plug in and extract the shots.

The recipes were recorded, each dose was measured to 0.1 of a gram and the output weight was consistently within 0.5g. The time frame was recorded and TDS was also recorded and tabulated, along with the calculation of extraction yield. All shots were run and recorded and 5 cups were randomly removed from each line up for tasting.

The espressos were only tasted when they reached 38 degrees Celcius to remove the chance of temperature affecting tasting scores. This temperature was measured using a handheld infrared thermometer. Each espresso was judged using the World Barista Championships (WBC) scoring system, with regard to taste balance and tactile balance. Any espresso 1 point outside the average in each bracket was considered inconsistent in taste.

So, what did we learn? 

What we found was the experienced barista was slightly more consistent with palm tapping than the inexperienced barista in relation to TDS. Also, when we observed the standard deviation, the OCD was more consistent for both the experienced and inexperienced barista. The OCD gained similar levels of consistency in extraction yield for both experienced and inexperienced barista, and there was less variance between baristas using the same method when comparing with palm tapping.

In terms of the taste, the OCD had no cups falling outside 1 point of the average for any barista, but each time palm tapping had 2 cups that had very inconsistent taste scores when compared with the other cups in the set.

What this shows is that TDS gives only a small indication that the extraction is the same, and that even though TDS was very similar between methods, the taste compounds varied significantly. Therefore, taste and TDS measurement both had to be taken into account when making a judgement call on consistency.

What does this mean?

This test has shown that palm tapping is, generally speaking, a relatively good method of distribution – however, it creates more inconsistency when different baristas come into play. A single barista may be able to replicate their method of tapping over and over, but this isn’t easily replicated across several staff members in a café environment.

As with any tasting test there are limitations and often, subjectivity can come into play. However, this tasting wasn’t recorded so much on preference as every score was done strictly to a scoresheet and was done blind to minimise bias. Only then were these scores analysed to look for inconsistency within a given set.

Obviously more data is always preferable – however, this testing gives a good indication of the OCD’s advantage over palm tapping for consistency between baristas. If you’d wish to learn more about the test and our findings, click to see the data:

 See experiment data


Watch the video 


Written by Hugh Kelly 
ONA Coffee Research and Development