First a great thank you to Susan Coppin and the team of archivists at the University of Adelaide who made recovering these documents possible.
All these documents from Australia were contained in Series 600 of the Roseworthy Agricultural College archives. We should probably figure out how to digitize all of the papers.
1. By reducing pH of base wine the ester content of brandy is increased.
2. Returning ‘heads’ and ‘tails’ from the brandy run to the next low wine charge causes an increase in esters, especially at pH 3.
3. Reducing the pH with sulphuric acids, besides being more economical, gives a higher ester content than tartaric acid, and at the required strength has no adverse effect on copper plate.”
“The purpose of my project is to show that by reducing the pH of brandy base wine results in an increase in esters, which are essential component of good brandy.”
“Our climatic conditions do not lead to high acid wines as in France, and thus we can only rely on reduction of pH, after fermentation, if we wish to increase the ester content of our brandies.”
“It is noticeable that the three main varieties are white, which are considered to be superior to red owing to less oils contained in skins and stems.”
“3. Sulphuric Acid:
Has been found preferable to use sulphuric acid in lieu of tartaric, not only for economy, from (VI) price of H2SO4 3d, a lb. against 4/6d. a lb. for tartaric, but also because it gives superior results.
H2SO4 has a lower pKa value than tartaric acid. [omitting small chart showing pKa values]
H2SO4 being more highly ionised will react with the potash neutralizing the tartaric acid, forming K2SO4 and releasing tartaric acid.
[omitting some simple formulas that are hard to re-type]
Thus reducing the pH with H2SO4 increases the content o tartaric acid.”
“Expressing results statistically confirms the hypothesis that the lower values of pH give more esters, as under. Although a significant difference between the two acids, statistically it may be due to chance.”
Tummel goes on to calculate the statistical significance of his results, but it should be noted his sample size is really small.
“The S.S. due to pH can be further portioned into a linear component and a quadratic component by means of orthogonal polynomials.”
Quite the over achiever. You do not see much of this math in early experiments. I think Maynard Amerine was also big pioneer of adding statistical analysis to his experiments.
Distillers may be dubious of the value of sulphuric acid for fear of its action on the still.
Following experiments proves H2SO4 may be used safely at the required strength.”
“From the above results, H2SO4 has less adverse effect on Cu, than Tartaric.” I don’t think you can draw much conclusions from so brief an experiment but experiments could definitely be performed. I suspect wooden boilers were used in the past for highly acidified mashes.
“Referring to table of analysis, page 7, reduction of the pH of brandy base wine has no significant effect on secondary constituents, other than esters, thus after part one, only analysis of esters was carried out.”
“The behavior of the ester content in the distilled spirits shows that as the concentration in the wash increases, the tendency is for a marked increase in the resultant heads, and to a lesser degree an increase in the brandy run, whilst the esters in the tails diminish or remain steady.”
“Although H2SO4 has been termed the “acid find” for reducing the pH of brandy base wine, it is here alone useful. H2SO4 could not be applied to marketable wine for the same purpose, as the legal limit of sulphate in wine is 2 grams per litre expressed as K2SO4.”
There is organoleptic analysis in the appendix mostly in the form of an inarticulate chart so I’m not sure how to interpret it. I think some tasters preferred the non-sulphuric acidified brandy to the tartaric. The experiments are unfortunately over simplified because they do not look at the distribution and variety of the fatty acid ester precursors.
Nothing unique was in Tummel’s bibliography.