H.T. Davoren. 1955. The Effect of pH on Brandy Composition

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.

Davoren, H.T. The Effect of pH on Brandy Composition. 1955. from Series 600 University of Adelaide Archives, Inventory Identifier 060000059 Box Number 2. [PDF]

This paper is concerned with ester production within the still. Cognac distilling material differs significantly from Australian distilling by pH and total acidity.  Acidity is a catalyst for esterification.  The author explores the correlation between ester production and pH.

“we can only rely on reduction of pH, after fermentation, if we wish to increase the ester content of our brandies.”  I suspect this will get them closer but not be equivalent.  The wines will still differ markedly by ester already present in the wines and the distribution of types of fatty acids (ester precursors).

“Two other factors which determine the composition of a brandy are the type of still and the method of distillation.”

“It is generally accepted (1) that only good quality brandy can be made with a pot still; 90% of French brandy is made with pot stills.” Some of the other Roseworthy papers elaborate this idea more.

“In the method of distillation the main consideration are:-

1. The strength at which the spirit is distilled.

2. The speed of distillation.

3. The distribution of impurities in the fractions.

4. The separation of the ‘heads’ and ‘tails’.”

The strength at which the spirit is distilled effects the distribution of impurities. What I hadn’t noticed before is how the recycling of fractions besides allowing for more time under heat for aroma precursors, also increases alcohol content by averaging it up and effects the distribution of congeners.

The speed of distillation also effects the distribution of impurities.  A slower distillation, which means more time under heat, allows for more aroma creation processes like esterification, but also is less challenging to the subtle reflux provided by the shape of the still head.  I originally suspected a minute amount of pressure could build up during a fast distilling thus slightly altering the distribution of the fractions but it turns out the reflux from the head of a pot still is more significant than I thought.

“Australian brandies approaching French style could probably be produced in dry wine areas, such as the Hunter River, but this would be uneconomical as there is a ready market for these wines.” Brandy production is most of the world is from areas where second tier grapes are grown.  There isn’t much need to make brandy if you are already getting great money for dry wines.  This economic look makes me wonder if brandy production could help jump start unique wine growing areas of the U.S. before global warming turns them into prime dry wine growing regions.

“I’ve heard that after World War 1 a firm was formed at Allandale, in the Hunter district, which made good French style brandies from local wine but, unfortunately, didn’t last for long.”

“In order to bring the acid content of Australian base wines to a level favouring maximum ester production it is advantageous to make acid additions to the wine, so bringing about an alteration in pH.”

“Tummel states the best way to reduce the pH is by means of sulphuric acid. He found that the spirit produced from wine in which the pH had been reduced by sulphuric gave a slightly higher ester content than that made from wine in which the pH had been reduced to the same level by tartaric acid, as well as the fact that sulphuric acid is more economical to buy than tartaric.”  Tummel’s paper is this collection.  He even does some cool regression analysis to look at the significance of the differences between sulphuric acid and tartaric acid.

“The effect of sulphuric acid on the copper of the still was also investigated by Tummel and he found that relatively no reaction takes place, and that wine treated with sulphuric causes less damage to the copper than that to which tartaric acid has been added.”  Damage to copper of extra acidified distilling material has been one of the things I haven’t been able to find much on.  My theory is that wooden boilers were favored in rum production where the distilling material is so acidified with sulphuric acid (in the dunder) that it would wear down a copper boiler quicker than is acceptable.

“2. Hydrometers.

There was no spirit safe supplied with the still so a means had to be devised for taking strength readings on the spirit as it left the condenser.  A number of glass bubbles were made which just floated in spirit of varying strengths, ranging from 40° O.P. to 100° U.P. (water).

The bubbles were placed in a separating funnel which was clamped under the spirit take off from the condenser, and the spirit level in the funnel was kept constant by means of the tap.”

What is being described here are called “spirit bubbles” or “philosophical bubbles” and were a very early form of hydrometry which predated the modern hydrometer which a floating scale. They are extremely rare and I actually acquired a complete set which I found in the UK. I had to pay $300 USD.  It is really exciting to seem them used in this scaled down experiment.

Davoren explores pH’s 2.5, 3.0, 3.5, 4.0, and 4.5 in his experiment. He raised or lowered the the original pH of 3.22 with calcium carbonate and sulphuric acid respectively.  “In each case the rates of addition were determined by trial before the bulk was treated.”

“After the calcium carbonate was added it was well stirred in and the calcium tartrate formed was allowed to precipitate over night.  The clear was then drawn off and checked for the correct pH before being stored in readiness for distillation.”  Separating precipitated tartrates might be useful in some of my experiments where I tried to make a brandy from vinegar tainted cider. Removing the tartrates might mean that acetic acid can be removed then alternate acids like tartaric can be added without being interfered with by the tartrates.

The experimental still had a frothing and puking problem and Davoren has to add some glass boiling stones.

The experimental still also uses a brandy ball which I have yet to find a diagram of.  I suspect it is just water run over the still head to create small amounts of extra reflux which out having to construct a typical column.

Some of the samples have to be distilled again due to puking.  I can’t figure out if Davoren has over filled his small still or if the change in pH has made some of the samples froth more.

“Both ester curves decrease slightly as the pH increases, whilst the decrease in each case between pH 2.5 and 3.0 is practically negligible.  It appears therefore that reducing the pH of the wine to 2.5 doesn’t case any further ester production than does reducing it to pH 3.0.”  This result makes me curious about rum production practices.

“The increases in aldehyde form the higher to the lower pH is considerable, but if the heads portion were removed, as is usual in commercial distillations, most of the aldehyde would be in these fractions.” Davorens experimental distillations were uncut.


1. [de]creased pH of the base wine does give an increase in ester formation, with the maximum pH for such increase being about pH 3.0, but this might vary if only the brandy fraction of the run is taken.

2. The lower the pH of the base wine the more aldehyde is formed, which would probably necessitate the running of more spirit into the ‘heads’ fraction when distilling low pH wines.

3. The results for the acid formation are too erratic to draw any worthwhile conclusions.  It should be a fact that the lower the pH the more acid formed but this doesn’t seem to be the case, in A curve and in B the curve reaches a peak at pH 3.0 but falls away again.”

Most of Davoren’s bibliography consists of the Roseworthy projects I’ve collected.

One cool thing he and other people list is “R.A.C. Distillation notes.” I wonder if it could be found in the archives.  A search through the archives for the Distillation Notes shows that Roseworthy was making its own brandy which was sold on campus tours.  It would be really cool to find more details about it.

This might be worth digitizing: Roseworthy Distillery Survey Account Book

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