Initially posted: 15 Dec 16
Updated: 22 Mar 17
The goal of this study was to explore the impact of the OCD distribution device on espresso as measured through total dissolved solids (TDS) extraction with a coffee-correlated refractometer (VST LAB III) and shot time. The dependent variables collected were shot time, beverage mass, and TDS. Independent variables included: 1) use of the OCD/no OCD and 2) grinder. Results showed a significant reduction in TDS/extraction yield using the OCD (p < 0.00), a significant difference in TDS depending on grinder used (p < 0.00), and a significant interaction of OCD x grinder (p < 0.00), as well as a significant effect of grinder on shot time (p < 0.00) and a significant interaction between grinder and OCD (p = 0.03). An additional test, following similar procedures as those outlined here, was performed comparing the OCD 2, another distributor tool (shown here, referred to as “BT” distributor), and no distributor. Results showed a significant reduction in TDS/extraction yield only with the OCD 2 compared to the control condition (p < 0.00) and compared to the BT distributor (p < 0.00). No statistically significant difference was seen between the BT distributor and control condition. Results shown here.
Based on our data, use of the OCD and OCD 2 consistently led to lower TDS in espresso shots (and corresponding extraction yield, given all conditions had equivalent final beverage mass). We also observed different grinders led to significantly different extraction levels, with the Mythos One having consistently less variability compared to the K30 and Anfim. Lastly, the interaction effect suggests the impact of the OCD on TDS varied based on the grinder used, but this is most likely due to the overall reduced variability seen with the Mythos One grinder relative to the other grinders.
We have no vested interest in any of the products being used for this experiment. All products used in this experiment were purchased by Socratic Coffee team members.
Jeremy and Joe
After dosing ground coffee into a portafilter basket, very often the coffee is unevenly distributed. To more evenly disperse coffee throughout the basket, baristas have adopted a variety of different techniques. In the past few years, a surge of tools to help with this process have emerged. The mechanisms of action between these various tools may vary to some degree, but the end goal is the same: more evenly distributed coffee grounds in the portafilter basket, potentially creating more uniform density throughout the puck before it is tamped.
The three main hypotheses for this experiment were 1) use of the OCD would lead to significantly higher TDS/extraction yield, 2) the grinder being used would have a significant effect on TDS, and, 3) no significant interaction would be seen between use of the OCD and grinder.
The coffee used for the experiment was a blend of Ethiopian Sidamo Guji and Brazil Mogiana. Coffee was rested for 7 days before use. The same batch of roasted coffee was used for the entire experiment. Room temperature was between 19°C-24°C and humidity 65%.
- La Marzocco (LM) Linea ABR, two group fitted with 0.6 mm restrictor and standard double portafilter with the 20g VST basket filter, set at 9 bar water pressure (verified with a Scace II); brewing temperature 94°C regulated with a PID on board, built-in scales were calibrated prior to the experiment
- Water filter used for the experiment was Brita Purity C150 Quell ST
- Anfim SPII Special Performance / Mythos One / Mahlkonig K30 coffee grinders (once dialed in using the OCD for each grinder, the grind setting was maintained for all conditions–beverage mass goal of 40g in 30 s)
- Two scales (Ohaus Navigator XL calibrated prior to the experiment to measure the dry coffee dose)
- Pen and paper to record values
- 50+ empty ramequin bowls for measuring the mass of the shot
- 50+ empty small ramequin bowls for TDS measurement
- Pullman TampSure ensuring same depth tamping no matter how much pressure is applied (depth exceeded that of the maximum point of the OCD by more than 2 mm)
- Portafilter stand
- OCD Distributor
- Brush to wipe off coffee of OCD
- VST LAB III 4th Generation refractometer, zeroed according to manufacturer guidelines
- Distilled water
- Alcohol pads
- Infra-red gun to measure the solution prior to refractometer measurement (under 30°C degrees, average 27.5°C)
- Microfiber towels
The conditions with the grinder and espresso machine were constant for all conditions. The room temperature was controlled with air conditioning at approximately 24 °C for the duration of the experiment.
Within a specific grinder, the condition order (OCD/no OCD) was randomized. Further, three experimenters were used. One experimenter dosed and distributed coffee in the basket (using the OCD or gentle tapping).
- OCD Dosing: The dosing of the OCD was carried out consistently all across coffee grinders. Each shot of coffee was ground and carefully dispensed in the middle of the portafilter. Weighing the amount of coffee in the portafilter on the scales, some of the shots required adding/removing +/- 0.5-1g of coffee and this was done by using a small spoon. The portafilter was placed on a stand and each shot was distributed with an OCD, occasionally using a small brush to remove ground coffee was stuck on the base of the OCD due to static. The portafilter was re-weighed to make sure the dry dose of coffee was 20g. The portafilter was then carried to another experimenter who tamped the coffee consistently using the TampSure and portafilter stand, as well as pulled the shot to the beverage mass goal, recording shot time. A final experimenter measured the shot TDS.
- NO OCD Dosing: The dosing of the No OCD was carried out consistently all across coffee grinders. Each shot of coffee was ground and carefully dispensed in the middle of the portafilter. The portafilter was gently tapped on the fork of the coffee grinder** and weighed on the scales by adding or removing any necessary coffee (+/- 0.5-1g of coffee). The portafilter was then carried to another experimenter who tamped the coffee consistently using the TampSure and portafilter stand, as well as pulled the shot to the beverage mass goal, recording shot time. A final experimenter measured the shot TDS.
**Because the incorporation of a “gentle tap” differed between OCD and No OCD conditions, we did a study specifically to assess any impact a gentle tap versus no tap may have. No significant difference was found between tap and no tap.
A brew ratio of 1g coffee to 2g brew weight was used (i.e., 20g dose for 40g final beverage mass). Because TDS is most strongly correlated with beverage mass, shots were all pulled to a consistent mass. Time to reach this weight was recorded. Shots were performed at 9 bar pressure
All TDS samples were performed following VST recommended guidelines.
All analyses were performed using R 3.1.1 and Excel 2016. Data was first analyzed with de-identifying generic labels and matched via a key to the appropriate conditions after analysis was complete (i.e., data was analyzed in a blind manner). Data was first assessed to ensure it does not violate assumptions for multivariate analysis of variance (MANOVA) using Condition (OCD/No OCD) and Grinder (K30, Mythos, Anfim) as independent variables and Shot Time and TDS as dependent variables. Beverage mass values between conditions were compared via t-tests and revealed no significant difference. A MANOVA utilizing the Pillai test, showed a significant effect of Condition (F(1,54)=61.5, p<0.00), Grinder (F(2,54)=14.6, p<0.00), and Condition x Grinder (F(2,54)=3.5, p<0.00). More specific ANOVAs and contrasts were then utilized to better explore relationships in the data (outcomes shown in figure below).
For total dissolved solids:
For total dissolved solids between the OCD 2 and BT distributors:
For shot time:
(Raw data can be downloaded in a tab delimited text file here--and OCD2/BT testing data here. As always, while we offer the data for your personal use, we kindly ask that you send a message to firstname.lastname@example.org before posting or presenting it in any public forum and attach appropriate acknowledgement.)
Because our dose and final beverage mass does not vary significantly between conditions, any differences observed in TDS can be extrapolated to differences in extraction yield (EY). Our last hypothesis, regarding the interaction between the independent variables, would suggest that an effect seen when using the OCD would be evident with all grinders. This could be related to consistency in the OCD’s effect. Our results may suggest variability inherent in the grinder itself with regard to TDS/EY can overcome any negative impact on extraction created by the OCD.
Did the OCD lead to more consistent extractions? Given our data, this does not appear to be true. Using our metrics (TDS and shot time), “more consistent” would imply “less variability within a condition”. The amount of variability did not vary between OCD and non-OCD conditions. The most consistent effect was a reduction of shot TDS when using the OCD. For shot time, in two of the three grinders used, there did appear to be a slight reduction in overall variability after use of the OCD (the significant interaction effect). However, this was not seen for all grinders and did not alter the overall extraction of dissolved solids.
Why the OCD consistently reduced extractions is not clear. Tamping provides a compression force to coffee particles in a puck. The OCD device may apply a significant amount of shear force. Why the OCD’s effect was so pronounced with all grinders only in TDS and not shot time is also not understood. Any negative impact the OCD may have on coffee particle arrangement, bed architecture, etc. that could potentially impact extraction would seemingly have a corresponding impact on shot time.
We intentionally did not collect or present any subjective data. We feel it is the role of the barista/café owner to determine the desired taste given his/her equipment, coffee, water, and preference. Our data is meant to compliment and better inform the coffee community so that they may arrive at their desired taste more efficiently, effectively, and consistently. It is possible the OCD shots of lower TDS/EY would be preferred by the barista/consumer. Further, while somewhat unlikely, it may be possible that the content of extracted solubles differed when using the OCD.