It used to be that the characteristic of Hunter Reds was a “sweaty saddle” nose that would signal Hunter! Not any more, with great perseverance the Hunter wine industry has got rid of Brettanomyces (Brett) – the organism that was spoiling our wines. Although for years it wasn’t recognized, the flavour can be attractive to some. Brett, as spoilage yeast, is sensitive to Sulphur Dioxide and often becomes a problem if sulphur levels fall or it may be omnipresent in the barrels of a winery, reflecting poor hygiene techniques. The elimination can be a costly experience and today we take great care with our barrels, particularly where exchanges may occur between wineries.
Spoilage in wine and beer has been a problem over the centuries and was not understood until the famous French scientist Louis Pasteur made his ground breaking discovery, living bacterial spoilage. With the aid of his microscope, he led us to an understanding of the role of yeast in fermentation.
Pasteur made two important discoveries from the spoilage of beer, first the beer was ruined by lactic acid that was produced by a living organism, the Lacto bacillus – a bacterial organism (he published this in 1857) and secondly alcoholic fermentation was as a result of fermentation by living yeast (published in 1860).
Pasteur proved through experimentation that living cells, yeasts, were responsible for making alcohol from sugar and that contamination from living microorganisms could turn the fermentation sour.
These were revolutionary discoveries. Prior to this “spontaneous generation” had held sway as the basis for fermentation – a theory going back to the Greek philosophers such as Aristotle in the 4th century BC. It was thought, for instance, rats appeared in garbage through the process of spontaneous generation!
In the 1830’s, yeasts were first seen through the microscope in fermenting beer. Many theories developed including the concept that dead yeasts acted as catalysts for fermentation or that water dispersed the yeast cells that became small animals, devouring the sugar and that alcohol was part of their excretions! Both these ideas were put forward by the leading scientist Justus von Liebig struggling to find an explanation. The science was NOT settled!
Pasteur showed that the yeasts and bacteria could spread through the air or be present on grape skins. In the absence of these living organisms, no fermentation occurred.
Pasteur’s classic experiment was to put a sterilized sugar solution in a sealed flask and nothing happened. On breaking the glass, contamination from the air occurred that led to fermentation. When alcohol was produced the yeast were plump and budding, if lactic acid was produced small rod like microbes appeared.
Amazingly the son of a wine merchant in Scotland with a strong interest in optics and microscopes, Joseph Lister read Pasteur’s papers. In the early 1860’s and with the aid of his father’s microscope, Lister concluded that “laudable pus” which flowed from infected wounds was caused by microbes from the air and surrounding surfaces. He also revolutionized surgery with the use of antiseptics in particular carbonic acid, used to clean the skin, operating theatres and surgical instruments etc reducing dramatically the incidence of wound infection…the rest is history as they say but it did not come easily. As late as 1908 many hospitals in Sydney had not adopted the Listerian approach. Paddy Moran the surgeon and first captain of the Wallabys went on after the rugby matches to Edinburgh to study Listers approach and bring it back to Sydney!!!
Nor was it easy for Pasteur to convince the scientific community he was right and indeed he could not explain how the yeast in fact did the conversion.
A long running dispute between Pasteur and Justus Von Liebig ( discoverer of the importance of Nitrogen, Phosphorous and Potassium to plant life) ensued.
📷Liebig was incidentally a member of the Hunter River Vineyard Association (HRVA). He had long standing correspondence with James King of Illawang and issues regarding yeast had been the subject of some of their exchanges. King had observed that Verdelho grapes with high sugar content sometimes failed to ferment to dryness and then would turn into vinegar. His solution was to add some actively fermenting grape must to the stuck ferment increasing the yeast content and helping to complete the ferment. King used a saccharometer to measure the sugar, but at that time had no way of measuring the yeast.
By 1852 the process was not understood, but many still felt fermentation was a “series of chemical transformations” i.e. occurred by the age old process of Spontaneous Generation – the microbes appearing spontaneously leading to a strictly chemical process. King’s ideas were counter to this popular belief and Dr Carmichael of Porphry Vineyard, a respected member of the HRVA, cautioned the association against Kings views of the yeast -not wanting the HRVA to be seen at fault in accuracy and knowledge, as well as in philosophy!
In the end it was the enzyme in the yeast that was found to do the work in 1897. The German scientist Eduard Buchner was awarded the Nobel Prize for observing enzymes from ground up. Yeast cells (non living) were capable of fermenting sugar to alcohol. So both Pasteur and Von Liebig had been in some ways correct but it was Pasteur who prevailed and changed the way we look at fermentation and contamination.
Contamination remains a problem in the wine industry and a good example was the loss of up to a fifth of fortified wine stocks in Australian fortified wines in the 1930’s due to the malolactic bacterium. This was particularly so for the South Australian and Victorian producers who concentrated on fortified wines.
The crucial finding was the presence of a high pH reading indicating a low acid level in the wines that was favorable to the malolactic bacteria. Penfolds in particular took a great interest and started measuring pH, particularly their chief chemist Ray Beckworth. At risk were the high yielding Riverland grapes. With the use of the pH meter, steps could be taken to make acid additions and correct the fault. As always people needed to be convinced of the scientific facts but once accepted it eliminated malolactic spoilage and saved millions of liters of wine and produced millions of pounds of income!
Wine making is both an art and a science, the art is often in the selection and blending, while the science starts in the vineyard and follows in the winery. We need always to be on guard for the development of faults, diseases and issues of contamination.
Our Hunter pioneers were curious about the methods of grape growing and wine making and adopted a scientific approach…they had little to loose and much to gain.
Justus von Liebig contributed to our early understanding of winemaking and, as the acknowledged leading scientist of his day, his letter of encouragement to James King should be read as a significant complement and good advice to our fledgling industry.
The science is never 📷 settled and vigilance remains of utmost importance. Australia’s leadership in the science of viticulture and winemaking has put us in a good place and needs to be encouraged and not taken for granted.
Illustrations from Pasteur’s and Bruchner’s publications from the Fisher Library University of Sydney and The Maitland Mercury
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Author: Robert Lusby AM
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