From Brewing Science and Practice
8.2.3 Analysis of the hop resins
Procedures for the estimation of the total resins, total soft resins, and hard resins, by difference, (see definitions above) in hops and hop products are given in Analytica-EBC but since it was found that the A-acids are the most important brewing principles few brewers bother to measure the total and soft resin contents. The _-acids were originally estimated gravimetrically as their lead salts but since the precipitate is soluble in excess of the lead acetate reagent, trials had to be made so that only the correct amount of reagent was used making it a lengthy process.
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It was found that if the conductivity of a methanolic solution of the A-acids was measured during titration with methanolic lead acetate solution it did not increase until there was an excess of the reagent. Thus if regular aliquots (0.20 ml) of the methanolic lead acetate reagent (2 or 4%) are added and the conductivity measured after each addition, a graph can be drawn where the intersection of the two straight portions provides the endpoint (Fig. 8.5). The absolute value of the conductivity is not needed and the lead acetate reagent can be standardized by a similar titration against 0.100 N sulphuric acid. The shape of the graph is different in the presence of other solvents, so, in the approved method, pyridine (1 ml) is added to the titration. The conductivity may be plotted against the volume of the reagent on Cartesian coordinate paper (Fig. 8.5) or the resistance may be plotted directly on to reciprocal ruled paper. Since the reaction of lead acetate is not specific for A-acids, the result is expressed as the Lead Conductance Value (LCV). However, with fresh hops the LCV is very similar to the A-acid content but, as hops age on storage, oxidation products are formed which may react with lead acetate.
Hope that helps
MHB
Cheers MHB, thats all in line with what ive read so far, for bittering calculations LCV seams to be a very useful measure. Especially for home brewers. Personally i dont consider the other hop oil components when designing a beer so it seam very useful for young and old hops. Picked up 4L of methanol today, its denatured metho, should be fine for this purpose.
Heres to yellow salt!!!
Very useful that the actual conductance isn't so important as is the turn point interpereted on the chart.