Gluconic, lactic and succinic acids are also formed. The levels formed depend on apple variety, juice treatment, yeast strain, fermentation conditions, and storage conditions. In general, low pH and low nitrogen levels tend to produce ciders with higher fusel alcohol levels. Use of sulphur dioxide, and centrifugation of the apple juice before fermentation both result in the lowering of fusel alcohol levels. The factor most affecting fusel alcohol levels is the strain of yeast.
Aeration is also a factor, aeration reduces fusel production markedly.
The maturation phase of cider production includes the malo-lactic fermentation. In this stage, malic acid is converted to lactic acid and carbon dioxide. The nearer the pH is to 3.0, the more delayed is the onset of the malo-lactic fermentation. As well as the conversion of malic to lactic acid, this fermentation also sees the production of quinic and shikimic acids both of which are essential for a good flavour balance. First pick your apples.