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.
Walters, J.R. The effect of the tartaric acid content of wine on the composition of distillates. 1947. from Series 600 University of Adelaide Archives, Inventory Identifier 060000021 Box Number 1. [PDF]
The Series 600 index does contain a typo. The study is about tartaric acid and not lactic acid.
This is another study pertaining to the old adage that high acids wines make the best distillation material.
“However, little is known of the effect of the composition of the base wine on the distillate.”
“This acid [tartaric] is the characteristic acid of the grape and is predominant in over-ripeness, being present as bitartrate and tartrate salts which are precipitated to a considerable extent during fermentation. It is a usual addition in the acid form during vintage operation and, when this is practiced it represents a considerable portion of the acid in the finished wine.”
“In literature dealing with the production of cognac, the fact that wines are always of high acidity is stressed. In under-ripe grapes malic acid would be predominant but this would not be so under Australian conditions where grapes for distillation are usually picked at extreme ripeness.”
“Renee and Jean Lafon (6) state that tartrates in solution with wine distilled on lees react with alcohols giving esters.”
“Aldehyde is an undesirable impurity in brandy in large amounts and its elimination or production in small quantities is important in the distillation of high quality pot brandies.” Walters references Angove that distillation on lees produces less aldehyde.
“Esters are said to be produced to a limited extent during distillation. They are the important flavouring constituents of brandy and their formation appears to be related to acid content. The bearing of tartaric acid content on the amounts of these constituents present in the distillates is the object of this experiment, the theory being that a higher ester and low aldehyde content would result.”
“Figures show a slightly lower alcohol content in wines fermented at the low pH which may be attributed to the inhibiting effect on the yeast. This also accounts for the high residual sugar and differences in volatile acidity.” Inefficient fermentation might create different degrees of the “mosto-verde effect” where skewed ratios of aroma to alcohol are created.
“Considerably higher values in acids in AI and AII are due both to higher volatile acid produced during fermentation and to carrying over of some non-volatile acids during distillation.” Here is where the study might have a problem. No non-volatile acids should come over unless he is running the still incorrectly. Because some of these students used small stills that were too full they had problems with “puking” where non-volatile material bubbles over into the condenser. Maybe Walters will give more hints later on.
“It is probably that there is a slightly lower production of aldehyde during fermentation in an acid medium. Acetaldehyde is a normal product of fermentation in small amounts. In the final stages of fermentation it is said to be converted to alcohol by reduction due to enzyme action. The change in pH would effect the activity of the enzyme and hence the products of fermentation.” I have not heard of this enzyme idea but it is really interesting.
“In the first distillation to low wines some tartaric acid could be carried over during the boiling and in view of Angove’s work (1) it appears that the process of distillation itself has an effect on aldehyde production which varies with different concentration of tartaric acid or tartrates in the wines.” I think that tartaric acid could be carried over is only a hypothesis and the way it is stated doesn’t necessarily mean that Angove had any similar hypothesis. Tartaric acid to the best of my knowledge is not volatile in the context of beverage distillation. Unless the still is operated incorrectly such as filled too high there should be no tartaric acid in the distillate.
“A lower ester formation from the more acid material is shown which is contrary to what would be expected and is difficult to account for. It is quite evident that this acid has no importance in regard t increasing ester production.” Other studies found sulfuric acid to be a better catalyst for esterification than tartaric. I’m not sure what happened here.
Walters proposes experiments that link acid content of the wine to aldehyde content. He states that if aldehyde content could be reduced in the wine a smaller heads cut could be made therefore increasing economy. He runs out of time to conduct any further experiments.
The paper is fairly short but has a large appendix of his methodologies.