Examining the Impact of the OCD (and OCD 2) on Total Dissolved Solids Extraction

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Initially posted: 15 Dec 16

Updated: 22 Mar 17

Abstract

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.

Bottom line

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.

Disclosures

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.

Authors

Jeremy and Joe

 

Introduction

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. 

Methods

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%.

Equipment used:

  1. 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 
  2. Water filter used for the experiment was Brita Purity C150 Quell ST
  3. 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)
  4. Two scales (Ohaus Navigator XL calibrated prior to the experiment to measure the dry coffee dose)
  5. Pen and paper to record values
  6. 50+ empty ramequin bowls for measuring the mass of the shot
  7. 50+ empty small ramequin bowls for TDS measurement
  8. 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)
  9. Portafilter stand
  10. OCD Distributor
  11. Brush to wipe off coffee of OCD
  12. VST LAB III 4th Generation refractometer, zeroed according to manufacturer guidelines
  13. Distilled water
  14. Alcohol pads
  15. Infra-red gun to measure the solution prior to refractometer measurement (under 30°C degrees, average 27.5°C)
  16. Pipette/Serviettes
  17. 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.

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Results

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 info@socraticcoffee.com before posting or presenting it in any public forum and attach appropriate acknowledgement.) 

Conclusions

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.

 

16 Responses

  1. Philip J. Espresso

    Would the use of the OCD merely act as a wave type initial tamp followed by a distribution of remaining loose material? Tamping after this would then compact further the initial wave tamp.
    The result, I feel, would be a more uneven tamp with water being led more predominantly through the channels that did not receive the initial impact of the OCD being pressed into the coffee.

    For this to be a useful tool, it may have to be able to rotate as it is being lowered into the basket and onto the coffee. This would encourage a more even distribution before tamping.

    • Look at the videos for the OCD. You rotate it to get even distribution.

    • That was the question in my head. Might lead to albeit, slight channeling…?

      • It’s hard for us to quantify channeling (and not possible given the approach used in this study). The mechanism by which the OCD reduced extraction is not clear. Perhaps it was due to increased channeling, we just can’t say for certain. In conditions with no distribution and direct tamping (“tap and tamp” as well as “no tap, just tamp”), the OCD reduced TDS but did not cause a significant difference in shot time. So if channeling was an issue, it was not enough to alter overall shot time–so maybe some form of “micro-channeling”?

  2. That`s brilliant!What a coincidence I was planing this experiment these days and already started ,of course not as this volume as you did (more than 60 is a loooot!).then I saw your work ,so much precise.
    Thank you very much for sharing this .
    And also ,can I translate your article into Chinese to share with Chinese baristas and coffee lovers?Of coures I will also post your original website at the same time .
    Again thankyou very much for sharing ackonwlage.

    • Hi Blake,

      Sure, with a link back to the original article and proper credit, translating it would be fine.

      Thanks,
      Jeremy

  3. Awesome write up guys, thanks for this info.

    Can you “unofficially” comment on taste preferences with and without the OCD you found through your experiments? As in, did you find the lower TDS shots had more even extraction and a better taste?

    Keep up the good work! 🙂

    • Hi Matt,

      Sorry, we don’t comment on taste… what does a “more even extraction and a better taste” mean? What does a more even extraction taste like? Does a better taste mean more sweetness or do you have a preference for higher acidity, greater body, etc.? After doing years of human performance research for a variety of applications, and judging for barista competitions, one thing that has become obvious to us are the challenges in subjective experience quantification (and qualification). The World Coffee Research’s Sensory Lexicon has attempted to bring some standardization to the subjective measurement and description of coffee’s sensory qualities by referencing sensory descriptions and strengths to non-coffee item standards. We think this is a great step in the right direction, but still far from allowing us to say anything like “this tasted more evenly extracted and better”.

      Best,
      Jeremy

  4. Thank you for your time and hard work putting this together.

    Great testing and methodology! I’d be very interested to see this testing repeated on the new Pullman Chisel Distribution Tool.

  5. Can I ask why you used a blend of coffee, when that would mean the solubility of each dose would most likely vary quite a bit? Also your dose weight +/- 0.5-1g, is that correct? It seems based on these factors the data can’t be consistent enough to draw any conclusions.

    • Hi Kris,

      Thanks for the comments.

      We simply used the coffee that was available in our lab in sufficient quantity at the time of the experiment. It is possible the solubility of each dose varied. This is why randomization is so critical in any experiment–it is a control against potential systematic confounds. A similar comment was made about our tamper experiment (comment itself found here on Instagram). Randomization, a methodological control we employ in all of our experiments, spreads potential systematic variability (e.g., variability in dosed coffee, shifts in grind distribution due to motor heating, humidity/temperature changes in the room over time) across conditions (i.e., OCD/no-OCD). So the order of shots pulled with or without the OCD varied randomly throughout the experiment. Further, consistency in our findings is seen when we repeated our methods with several different grinders, all showing the same pattern–that is, the OCD significantly decreased extraction.

      Controlling dose is something we are very careful to do with high precision. As stated in the write-up, “…some of the shots required adding/removing +/- 0.5-1g of coffee and this was done by using a small spoon.” We always adjust dosed coffee to measure exactly 20.0g for any experiment.

      Hopefully this helps assuage any concerns you might have.
      Jeremy

  6. Is there a way to have like a subscription email to your blog? These are amazing!

    • Not at this time–sorry! Your best bet is to periodically check our Instagram feed.

  7. Jeremy, how do you know the depth to adjust the OCD tool? You showed the image but its not really clear even in the ONA video. I’m assuming that the tool still compacts the ground coffee initially resulting in some of the ground being uneven in the basket. I would be interested in a comparison of the Saint Anthony distribution shot collar versus OCD. As the shot collar is applied prior to grinding the coffee, which may result in more even distribution and no pressure on the bed before distribution. Thoughts?

    • Unfortunately, we’re not sure how to determine the appropriate depth for the OCD tool. In our second bit of testing, using the OCD2 and another distributor (“BT”), we simply matched the final depth achieved after using both devices. And, in the end, all depths are made consistent with tamping. Thinking about why the OCD/OCD2 have given such a consistent finding, especially when compared to another distribution tool, really does seem to suggest some aspect of the initial compression might be the culprit. Maybe you’re right that the Saint Anthony collar is a better approach; though, the BT distributor led to no significant change from baseline (single, gentle tap), so it’s also possible that the devices simply don’t improve–but can possibly hinder–extraction.

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