Cider like wine is an alcoholic fermented drink. Alcohol is produced by yeasts. But it is essentially a by-product. The yeast is extracting energy from the sugar and releasing CO2 and alcohol secondary to this. Some yeasts especially the Saccharomycetes have taken advantage of this and become alcohol tolerant and can survive even thrive in alcohol concentrations that kill other yeasts and bacteria and so gain a survival advantage. All alcohol was made with wild or uncultivated yeasts for millennia before yeasts were discovered and cultivated. It is only in the last 100 years or so that yeasts have been bred with certain characteristics. This gives the modern cider maker options. Inoculating with a commercial strain guarantees a sure fermentation by flooding out the natural yeasts. These can even be killed off beforehand by the use of sulphur. Or more correctly sulphur dioxide a fumigant that kills yeasts and bacteria.
Yeasts were first discovered in the seventeenth century, by a Dutch tradesman named Antoni van Leeuwenhoek who developed high-quality lenses. In 1789 Lavoisier was interested in analyzing the mechanism by which sugarcane is transformed into alcohol and carbon dioxide during fermentation. When more powerful microscopes were developed, the nature of yeast came to be better understood. In 1835, Charles Cagniard de la Tour, a French inventor, observed that during alcoholic fermentation yeast multiply by gemmation (budding). His observation confirmed that yeast are one-celled organisms and suggested that they were closely related to the fermentation process. However our modern understanding of the fermentation process comes from the work of the French chemist Louis Pasteur in 1876. Pasteur was the first to demonstrate experimentally that fermented beverages result from the action of living yeast transforming glucose into ethanol. Moreover, Pasteur demonstrated that only microorganisms are capable of converting sugars into alcohol from grape juice, and that the process occurs in the absence of oxygen. He concluded that fermentation is a vital process, and he defined it as respiration without air
It is often thought that the wild yeasts needed to ferment cider reside on the apples and in the orchard. In fact they are quite rare here, it is another genus of yeasts Kloeckera apiculata that are found there. These can ferment but are killed by their alcohol waste at around 2% . At that point Saccharomycetes takes over so a succession of yeasts can occur that can develop a wider palate of flavours for us the cider drinkers. These are causes by esters in the fermentation process. The exact blend of strains of yeasts , hopefully mainly saccharomycetes that build up in each cidery is unique and is part of the terrior of cider making. They may have originally come from a few apples or blown into the cidery or remain from previous inoculations. They ‘overwinter on the walls , on cider equipment and on the pressing cloths. Cider makers are loathe to clean out the cobwebs incase they lose this source of yeast than may have taken years to build up. Here at TeePee Ciders we used to use AWRI 350 a cultivated yeast used by Long Ashton Research Station in the 70s. It gives a more complex flavour profile that the more usual “champagne yeast” a Saccharomycetes cultivated from wild yeast collected in the Champagne region of France.
Sulphur is one additive we use. It has been used for millenia and is recorded being used by the Romans in wine making. Its use in cider making is well documented and the first reference is found in John Evelyn’s Pomona an annex to his book Sylva a mangus opus on English wood uses , the first book published by the Royal Society in 1664. Beale writes..
Sulphur kills bacteria and yeasts selectively are various concentrations. Today we can carefully titrate the amount needed rather than lowering a burning sulphur candle into the barrel!
Note Beale quips its harder on the spoiler yeasts than our lungs, he knew its effect on those with sensitivity to it or asthma.
To get the best results of a wild yeast fermentation a small amount of SO2 kills the spoiler yeasts whilst leaving the Saccharomycetes alive and therefore negates the need for an inoculated yeast. Luckily for us the ‘spoiler’ yeasts and bacteria and lower concentrations than the desired Saccharomycetes, and results in a cider with more than the one dimensional flavour profile of an inoculated yeast but avoiding the excesses of the full farmyard aroma of a fully wild ferment