Fermentation of the mash is one of the basic stages of making fruit rakija: it is where alcohol is actually made. It follows the crushing of the fruit. Yeasts that rested on the skin of the fruit find themselves in a liquid full of dissolved sugar and begin to multiply fast, breaking the sugar down into various compounds, mostly alcohol and CO2, the two main products of their work.
Alcohol is also the basic component of fruit rakija, and of every drink made by alcoholic fermentation. Besides these, much smaller amounts of many other compounds form, such as glycerol and acetic acid, and energy is released as heat, part of which the yeasts use themselves.
The amounts and proportions of these compounds, and the energy released, vary a lot, depending on many factors. What the yeasts do can be seen: the mash first turns very cloudy, then light bubbles form and a foam appears and begins to boil, while the temperature rises by 10, 20 or more degrees. How much foam forms and how hard it boils depends on the temperature of the mash, and on its make-up, the size of the vessel, the kind or culture of yeast, aeration and so on.
When fruit is crushed, a host of unwanted yeasts and harmful micro-organisms get into the mash along with the good yeasts, and in the right conditions they start unwanted processes:
- acetic fermentation;
- malolactic fermentation and biological loss of acidity;
- overly violent fermentation;
- hydrogen sulphide fermentation.
Unwanted factors, such as the wrong temperature, the make-up of the mash or unwanted micro-organisms, can also stop fermentation. Mash from rotten fruit, for example, ferments with difficulty and stops easily unless steps are taken: stronger sulphuring, settling the mash, or pasteurisation with selected yeasts.
Fermentation also stops at high temperatures, and an unfavourable make-up of the mash makes it more likely: a high concentration of sugar, too little acid, or a high content of SO2 or CO2. Whether fermentation runs properly or goes the wrong way depends on whether the mash offers the yeast the conditions it needs.
In short
Fermentation is crucial for a good distillate. If the preparation is poor, the distillation cannot be good either, and neither can the finished rakija.
