Stunning results. Color me skeptical.

Forgive me for asking, but did you filter the samples? If not, the %EY differences and variability of the Robur results might be due to lesser and more variable fines production by the Robur. Small differences in undissolved solids could have a big impact on measured %TDS while not having a significant effect on flow rate, mouth feel and the actual %EY.

I ask the question because I didn't see any espresso filters with your refractometer kit. VST supplies filters and detailed instructions for using them for espresso and other unfiltered brewing methods. AFAIK, Atago does not supply filters or indicate when they're required for accurate results.

Another possibility, though less likely, is that you used different sample cooling protocols for the Monolith and Robur samples. For example, you might have allowed the Monolith samples to cool more than the Robur samples, or you may have let them cool so long some of the liquid evaporated. The cooling process has to be long enough to get the sample temperature down while avoiding significant evaporation. The samples must be properly cooled to the same temperature range at which the refractometer was zeroed with distilled water. Although the Atago refractometer may be temperature compensated, that's only within a narrow range of the temperature at which it was zeroed.

If you did filter the samples and cooled them properly, then I'd say there's something wrong with the Robur's burrs. There shouldn't be that much variation in the grind profile. I get much more consistent results with my K10.

Thanks Vlad! Sorry if I missed it or if it's obvious but what were the shot times on the doubles and the ristrettos?

"Forgive me for asking, but did you filter the samples?" No, I didn't. I didn't use filters for Robur and didn't use filters for Monolith.

"Another possibility, though less likely, is that you used different sample cooling protocols for the Monolith and Robur samples." I used the same cooling protocol for Robur and Monolith. Before each measurement and after the shot was pulled and was cooling, a few drops of distilled water were used to clean the refractometer. Then one drop of distilled water was used to zero it out before measuring extractions. Water was wiped and one drop of coffee was dropped on the refractometer screen. The same process and the same cooling time was used for Robur and Monolith. In addition, cups that were used for coffee were placed on the cup warmer the same time before pulling a shot, while weighing coffee, so cups are the same temperature and don't affect coffee temperature and EY measurements.

Peppersass wrote:Stunning results. Color me skeptical.

Forgive me for asking, but did you filter the samples? If not, the %EY differences and variability of the Robur results might be due to lesser and more variable fines production by the Robur. Small differences in undissolved solids could have a big impact on measured %TDS while not having a significant effect on flow rate, mouth feel and the actual %EY.

I ask the question because I didn't see any espresso filters with your refractometer kit. VST supplies filters and detailed instructions for using them for espresso and other unfiltered brewing methods. AFAIK, Atago does not supply filters or indicate when they're required for accurate results.

Another possibility, though less likely, is that you used different sample cooling protocols for the Monolith and Robur samples. For example, you might have allowed the Monolith samples to cool more than the Robur samples, or you may have let them cool so long some of the liquid evaporated. The cooling process has to be long enough to get the sample temperature down while avoiding significant evaporation. The samples must be properly cooled to the same temperature range at which the refractometer was zeroed with distilled water. Although the Atago refractometer may be temperature compensated, that's only within a narrow range of the temperature at which it was zeroed.

If you did filter the samples and cooled them properly, then I'd say there's something wrong with the Robur's burrs. There shouldn't be that much variation in the grind profile. I get much more consistent results with my K10.

Targeted shot times were 30 seconds for doubles and 35 seconds for ristrettos, not counting 15 seconds preinfusion. Actual times were +-5 seconds.

sonofjorel wrote:Thanks Vlad! Sorry if I missed it or if it's obvious but what were the shot times on the doubles and the ristrettos?

Says who?

Balthazar_B wrote:Is it possible the variances were from attempting to single dose on a Robur, a use case for which it is spectacularly unsuited?

Just a data point of questionable value...

I got a set of the red speeds last week. I mainly got them for the less static they are reported to have and did not expect any actual change in flavor. I've pulled more than a few shots on them now and I have to say they are actually noticeably different, flavor-wise, than the standard burrs. Not sure if its worth the $$ difference and I haven't had them long enough to say that they are generally "sweeter" or "greater separation of flavors" or whatever, but blends that I am familiar with (Hairbender and Full Cycle) tasted quite different and better.

I think I would have gotten them originally just 'cause they look cool, but I didn't know they were available at the time. I rationalized a spare set of burrs and got them afterwards. I usually keep an extra set of burrs around "just in case"

Balthazar_B wrote:Is it possible the variances were from attempting to single dose on a Robur, a use case for which it is spectacularly unsuited?

While I have was suggestions to such effect, if that was the primary difference it would real deal the deal and give huge preference for the monolith over robur for home use. Keeping it filled with a hopper introduces everything from size to purge to stale coffee concerns.

Either way incredible write-up, exactly what makes home-barista so awesome.

Vlad, these are really interesting and valuable results and as @day says exactly what makes home-barista so awesome.

Peppersass wrote:Stunning results. Color me skeptical.

Forgive me for asking, but did you filter the samples? If not, the %EY differences and variability of the Robur results might be due to lesser and more variable fines production by the Robur. Small differences in undissolved solids could have a big impact on measured %TDS while not having a significant effect on flow rate, mouth feel and the actual %EY.

According to Socratic Coffee study, the filter do reduce the TDS% reading, but their use is far from norm. The Atago does not recommend them in espresso filtering. From comments section in that article:

Jeremy wrote:Unfortunately, the decision to filter or not filter your coffee (I'm using that term to mean espresso as well), is one that we cannot say you should or shouldn't do. The important thing is to only compare readings collected the same way. Our work suggests the VST syringe filters do significantly lower TDS. Looking at it more closely, we see that the filters retain some dissolved coffee solids as well as release something (not coffee) that can register as a dissolved solid (unluckily, this is not a 1-for-1, as the filters retain more than they release). We have asked Atago why they do not recommend filtering coffee and here is their response, "By using those filters and syringes the espresso is no longer the same as what people actually drink. Then we thought, what does the Brix (TDS) value after filtration mean?" This is a valid point and something to consider. Atago and MISCO (the VST device manufacturer), and lots of other manufacturers, make refractometers with a variety of industry scales. Interestingly, we have not found any of them selling sample filters. VST suggests the syringe filters' use is to remove noise in the sample and create a more stable reading. But one might ask, "A more stable reading of what?"

Personally, I do not filter my samples.