Apple juice fermented using its native microflora (yeast and bacteria) or what is sometimes called a wild fermentation, normally goes through three natural phases(1). Note that the length of each phase is impacted by temperature. The chart reflects a fermentation at temperatures of 14-22C (60-72F). The first phase or Yeast Growth is dominated by Hanseniaspora and Kloeckera genera of yeast. While Saccharomyces cerevisiae may be found in this phase, it really doesn’t take over until phase two. Phase two, Alcohol Creation, is the phase when sugar is converted into ethanol and it is dominated by Saccharomyces cerevisiae with Hanseniaspora and Kloeckera becoming undetectable. The final phase, Maturation, is dominated by Brettanomyces and Dekkera yeast and this can last well beyond the 27 days I’ve shown in the graph. This is also when Lactic Acid Bacteria, LAB, can perform malolactic fermentation and many other enzyme and chemical reactions can occur.
The use of sulfites before yeast growth and after alcohol fermentation as well as pasteurization or filtration at any point will alter this process and impact the flavor profiles created. Adding a commercial strain of yeast and changing the temperature can alter the process by speeding up or slowing down the phases. For example, inoculating with Saccharomyces cerevisiae will shorten or all together by-pass the Yeast Growth phase because the colony is artificially generated but the Maturation phase can still occur.
(1) W.F. Morrissey and associates, The role of indigenous yeasts in traditional Irish cider fermentations, 2004 The Society for Applied Microbiology, Journal of Applied Microbiology, 97, 647–655.
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