The Spent Puck, Puck Filter

It’s laborious to just accept that espresso grinds are nugatory as soon as you turn off a shot. I imply, composters like them. You can also make MDF out of them and chopping boards. You may even flip ‘em into espresso cups. However understanding that tea leaves will be reinfused 10–15 occasions, particularly within the case of sure aged pu-erhs, then why are espresso grinds so shortly consigned to the bin? What if the spent puck might be used as a filtration media for enhancing the readability and lowering the bitterness of the following espresso? We tried it, and it will possibly. 

Professor Abbott had been speaking to us for some time about chromatography and the way that could be used to separate astringent particles. 

Paper chromatography

Think about you place a small dot of black paint close to the underside of a strip of paper, then dip the sting of the paper into water. What occurs is the water begins transferring up the paper. The paper fibres act because the stationary section. The dots of paint aren’t simply an homogenous mass, they’re a mixture of pigments. Because the water rises, some pigments stick strongly to the paper so that they transfer slowly whereas others want staying dissolved within the water so that they transfer sooner and additional up the paper. 

If, as an alternative of ink colors, you do this with compounds in espresso, the compounds that may be anticipated to adsorb onto the paper extra simply, and thus journey extra slowly, could be the extra hydrophobic bitter compounds, not the great fragrant ones. And conveniently, espresso extractions are already properly organized in a column, in order that’s an excellent begin. Prof Abbott’s pondering was that, if we might simply prolong the peak of the column with some type of adsorbent media, then among the hydrophobic compounds may adsorb onto particles decrease down within the column as an alternative of popping out into the shot. It’s fairly potential this already occurs with longer thinner espresso pucks. This concept might even assist to elucidate why Lance Hedrick discovered a lot profit in switching to a narrower filter basket. (Lance is all about 49mm as an alternative of the usual 58.) 

The Experiment

Step one was to fully strip a puck of espresso of all its solubles to make it extra ‘adsorbant’. We then put this to the take a look at to see if the idea interprets to a noticeable style profit within the cup, and if there’s one thing on this thought that may work for a café or competitors setting. 

We knew there was going to be a style comparability on the finish of this experiment, so we wanted to verify the spent puck wouldn’t impart over extracted espresso flavours to the cup. Our objective was to take the puck as much as most extraction. After about three minutes of fixed move via the puck, the one discernible style was a particularly delicate rooibos-like flavour which was so dilute that you simply’d get extra style out of a rinsed filter paper. The measurable TDS of the espresso water after 180 seconds was <0.01 TDS.

First up, we tried pulling a shot via a complete spent puck. We used a extremely deep basket to permit us to squeeze in a double-puck, however in fact the shot took perpetually and a day to come back via (2 and a half minutes) for a grind setting that, for extraordinary photographs, would take 24 seconds. The primary few grams to exit the portafilter have been virtually pure water which had been retained within the spent puck. It turned clear in a short time that we’d must coarsen up lots or we’d must make the layer of rinsed grinds lots thinner. In the long run we settled on 2-, 4- and 6-mm rinsed puck filters. 

Outcomes

Determine 1: Whole dissolved solids (TDS) decreases with growing puck filter thickness resulting from dilution from water retained within the spent puck filter. No surprises right here. 

Measured TDS decreased progressively with growing puck filter thickness (see Determine 1). Management photographs recorded a imply TDS of ~10.1%. The two mm puck filter produced a imply TDS of ~8.6%. This means that, at this thickness, the discount in TDS is basically defined by dilution from liquid retained within the spent puck layer, reasonably than a discount in extracted materials.

At larger thicknesses, TDS declined additional:
• 4 mm: ~7.5%
• 6 mm: ~6.3%

However in fact, the move charge for the 6 mm was actually sluggish. Shot occasions went as much as about ~90 seconds so, unsurprisingly, extraction yield dropped, AND once we tried the identical strategy utilizing a grind setting that would obtain sooner move charges, our TDS dropped too low once more as a result of we wanted a extremely coarse grind. I believe we are able to say the 6 mm situation represents a unique extraction regime, circuitously akin to the thinner rinsed puck filters, so in case you do this, you’ll be tempted to skip the 6 mm pucks. This stated, as you’ll uncover under, the 6 mm obtained the very best astringency scores, due to this fact it’s value some additional exploration. 

Relative Extraction Yield (Corrected for Retained Water)

Realizing that the rinsed puck filters retained roughly twice their weight in water, to account for the dilution results this had on the espresso because it flowed via the spent puck filters, we labored out a ‘relative (undiluted) extraction yield’. We estimated it by measuring the TDS of the ultimate beverage after subtracting our measured LR within the puck filter. 

The ‘Management’ photographs averaged ~21.7% extraction yield. The two mm puck filter yielded ~21.3%, indicating no significant discount in extraction yield relative to manage.

At larger thicknesses, extraction yield declined:
• 4 mm: ~20.4%
• 6 mm: ~18.8%

Nevertheless, as famous above, the 6 mm situation required a coarser grind to take care of move, so this discount displays each elevated filter thickness and altered grind setting.

Astringency Rating

Determine 2: Astringency scores by situation (decrease values point out much less astringency). In our take a look at we discovered that every one puck filter circumstances appeared to scale back astringency relative to manage, whereas dilution alone didn’t.

Astringency scores decreased constantly with growing puck filter thickness (see Determine 2). On this examine, decrease scores point out much less astringency and are due to this fact most well-liked, whereas greater scores point out extra intense astringency.
• Management: ~6.3
• Management + water: ~7.0
• 2 mm: ~4.2
• 4 mm: ~3.2
• 6 mm: ~2.0

Dilution alone (Management + water) didn’t scale back astringency and, if something, barely elevated it. In distinction, all puck filter circumstances diminished astringency considerably.

The two mm situation produced a big discount in astringency in comparison with each management circumstances, regardless of having an identical TDS and relative extraction yield to the diluted management.

Relationship Between TDS and Astringency

The connection between TDS and astringency is non-linear. The management and diluted management circumstances reveal that lowering TDS via dilution doesn’t scale back astringency.

In distinction, the introduction of a puck filter produced a marked discount in astringency at comparable TDS ranges. The two mm situation, specifically, confirmed considerably decrease astringency than the diluted management at almost an identical TDS.

This means that modifications in flavour usually are not defined by focus results alone, however reasonably by modifications within the composition of the extracted liquid.

Determine 3: Relationship between TDS and astringency. The two mm puck filter situation reveals considerably decrease astringency than the diluted management at comparable TDS, indicating a change in composition reasonably than focus alone.

Abstract of Key Findings

2 mm puck filter:
• Achieved a considerable discount in astringency
• Maintained comparable TDS (vs diluted management) and relative extraction yield
• Represents probably the most beneficial steadiness of power and flavour

4 mm puck filter:
• Additional diminished astringency
• Started to scale back each TDS and extraction yield

6 mm puck filter:
• Produced the bottom astringency scores
• Required a considerably coarser grind, leading to very low TDS
• Circuitously comparable resulting from modifications in extraction circumstances

Conclusion

Everybody we’ve requested to do this technique to date has been shocked how straightforward ingesting and mellow the photographs change into when put via a puck filter. This isn’t actually to say that they’re the way forward for espresso. What you get is a number of dried fruit and mellow acidity. Additionally, rinsing a puck for 3 minutes is plenty of wasted sizzling water. So a greener strategy to this type of brewing may contain batching the rinsed-off grinds and dehydrating them. 

General, we discovered the two mm thick puck filter to be probably the most practicable (that’s about 5 grams of espresso). Two millimeters supplied the very best advantages of a discount in astringency with out compromising extraction, whereas thicker layers have been clearly efficient on the astringency entrance however unhealthy for extraction effectivity. 

May You Use Puck Filters within the WBC? 

Based on the World Barista Championship guidelines, the essential clause right here is part 3.1 Espresso (Ok)

 “nothing aside from floor espresso and water could also be positioned within the portafilters” 

This rule signifies that generally used puck filters reminiscent of AeroPress papers or steel puck screens — are technically not permitted, as a result of they aren’t espresso. Nevertheless, a layer of spent espresso grounds would adjust to this rule, since it’s nonetheless floor espresso, even when beforehand extracted. That stated, there’s a secondary threat: the technical scoresheet requires rivals to reveal cleanliness, together with cleansing the portafilter basket and sustaining a hygienic workflow. A very strict technical decide might interpret the presence of moist, pre-used espresso within the basket as a failure to correctly clear the portafilter between photographs, or as poor station administration, doubtlessly impacting cleanliness and hygiene scores even when the tactic is technically throughout the guidelines. For the espresso course, the direct technical scoring dangers are small and clearly outlined:

• Dry/Clear filter basket earlier than dosing = 1 level (Sure/No)
• Cleans portafilter earlier than insert = 1 level (Sure/No)

Each are scored as soon as per course (not per portafilter), so the full mounted publicity for these standards is 2 factors. Along with this, Station Administration/Clear Working Space is an enormous one for tech judges and is scored individually on a 1–6 scale. So there’s a little bit of threat concerned relying on how the workflow and cleanliness are judged.