Some of the arguments around the utility or otherwise of extraction measurements, the so called "proprietary" maths formulae used with the VST etc. created a nagging little itch in the back of my brain. Harking back to a previous career we used to extract and measure soluble components (mostly dyes and resins) from printing inks using a variety of solvents, alcohols, ketones or hydrocarbons depending on what we were after.

Anyway, the method used was about as far away from refractometers as you could get, and is set out below.

• A Method For Determining Total Extraction Mass of Solubles and Particulates from an Insoluble Matrix Immersed in a Solute.
  
  Apparatus: Filter paper, scale, vacuum drying chamber.
  
  Method: The filter paper is weighed then immersed in the extracted solute until fully saturated, then removed and shaken to remove excess solute. The saturated filter paper is then attached to the scale.
  
  Scale and filter paper are then inserted in the vacuum drying chamber and the mass of the saturated filter paper recorded.
  
  The vacuum drying chamber is then closed and the drying procedure initiated. Drying continues until there is no change in the mass of the saturated filter paper over a predetermined time period. (This time period is normally dependent on the volatility of the solute.)
  
  The mass of the dry filter paper, which includes any solubles and particulates in the original solute, is then recorded.
  
  We then have 3 recorded measurements:
  
  • Original mass of dry filter paper = A
  • Saturated mass of filter paper and solute including extractables = B
  • Dry mass of filter paper and extractables = C .
  Calculations:
  
  • Total mass of solute and extractables = B-A = D
  • Total mass of dry extractables = C-A = E
  • Total percentage of dry extractables in solution = E*100/D.
  Note: In circumstances where the solute may contain dissolved solids prior to being employed for extraction it is recommended that the solute be tested by the same method prior to the extraction procedure and extraction percentages be adjusted accordingly.

I'm pretty sure it would be much easier to do this sort of thing today, this was over 30 years ago and involved a massive vacuum drier, a fiddly manual beam scale and a fume cabinet. Apart from dipping a little round of filter paper in the solution and shaking it off, the whole thing could be automated and computerized ... kickstarter, anyone?

Alan

This strikes me as similar to dehydrating coffee samples, as has been done for at least 60yrs & continues to this day. This requires simple mass calculations that can be found in many brewing manuals...the CBI made it even simpler: 10ml samples of cooled coffee were dropped into foil trays, dehydrated, then weighed on a German made Sartorius Selecta balance scale to 0.0001g. Multiplying by 10 gives you %TDS.

EE Lockhart also appears to have been behind a document titled the "Direct Reading Coffee Hydrometer", publishing date seems to conflict with his tenure at CBI/CBC, but who knows how long it was kept on the back burner, or whether they previously used other hydrometers and were able to consolidate against dehydration results.

Both these methods are a means of getting a %TDS reading, converting readings to an accurate %Ext Yield are where the "trick" is. Lockhart apparently suggested using a chart to plot ext. yield...there are several variables that can throw that off.

As you note, dehydration is delicate & time consuming. Brew a cup of coffee and you may well need that entire cup to use a hydrometer. Both methods used by the CBI/CBC had a specific protocol, both are prior art declared in VST's patent. The selling point of the VST method is that it is quick, compares to dehydration oven accuracy (if you are careful) & uses just a few drops of coffee.

Your perception of what is "so called proprietary" isn't accurate, hence your nagging itch. You have fallen into the common trap of assuming that simple calculations have been declared as protected IP, this isn't so. Maths is a universal language, but new & useful processes based on math are protectable, if they weren't then the patent would have folded, as it would if prior art hadn't been declared.

Actually, the method described measured TOTAL extraction, including annoying bits of resins and pigments if you didn't get your solvents right, and was remarkably quick. Most of our time was spent faffing about with the incredibly sensitive manual scale, which was a major PITA.

Sample size even back then was only a few millilitres, spread out in a thin film in a 7cm diameter filter paper. By the time the vacuum dryer had chugged up to its full vacuum the samples were dry, but we would normally leave things alone for a minute or so while everything stopped vibrating. I would imagine that modern high precision scales, miniaturized vacuum apparatus and even smaller samples would make the process even faster. It certainly wouldn't surprise me to find that there is already a specialised machine being manufactured with no thought of the coffee industry in mind.

Alan