Rakija straight from the distillation of raw soft rakija is not yet fit to drink; it has to mature. Fresh distillates are sharp, the more so the lower their alcohol, and vice versa: sharp on the nose, rough and burning on the palate, still brash and restless, not yet a drink in the true sense. After distillation, spirits from grapes, plums and other fruit, as well as from grain, maize, sugar cane or agave, have a high concentration of ethanol, sometimes up to 75%, which gives an unpleasantly sharp smell and taste.
To turn such a distillate into fine rakija it must pass through several stages, depending on the fruit. Like wine, rakija needs to rest while its aroma and taste develop; afterwards it is harmonious, smooth and softer, with a pronounced bouquet.
Maturing in barrels
Rakija can rest in oak or mulberry barrels or in glass demijohns. Barrels of 100 to 500 litres or more are filled leaving 3 to 10 litres of empty space, so the rakija can expand if it warms and so oxygen can diffuse more easily: the oxygen in that space helps maturing a great deal. The lid or bung should not be closed completely; a little air should get in under it.
New distillate usually goes into new barrels to take on colour faster, while its taste barely changes. After at least 12 months it moves into older barrels to ripen slowly, and what was lost to evaporation is topped up with new distillate.
Maturing also depends on the strength of the distillate. The best strength for extracting the compounds of oak is 45–55% vol; a high alcohol content speeds up and intensifies the reactions that improve taste and aroma.
Time
A distillate should ripen for at least 6 to 8 weeks at room temperature; as a rule, the longer, the better. The exception is Williams pear, which ripens for only up to 4 weeks at room temperature. Forming the bouquet, the final stage, is thought to take at least 6 years. Quality rises for up to 20 years of keeping, holds from 20 to 30, and after 40 years may slowly decline.
The time also depends on the size of the barrel: the bigger the barrel, the longer it takes. The same maturity is reached in a 50-litre barrel in 2 years, in a 500-litre barrel in 5 and in a 10,000-litre barrel in 15, because a larger barrel has less surface per litre.
Egalisation
When rakija is kept in several wooden vessels, after a while they are blended to even out the quality, usually halfway through the total keeping time. The strength is corrected several times along the way, never by more than 5% vol at once, with distilled or softened water (up to 30° hardness), or with alcoholised water (up to 25% vol) that has rested in a new barrel for six months.
Vessels
The vessel depends on the fruit. Šljivovica, kajsijevača, jabukovača and vinjak, and sometimes lozovača and komovica, usually mature in wood and take on a golden-yellow colour and a pleasant taste and aroma. Pear and apricot rakija are most often kept in vessels that give no colour.
Old oak is irreplaceable for top-quality rakija. The staves must be dried, seasoned and “wined”: oak is dried for at least 3 years to the humidity of the room where the barrels will be used, then rinsed with steam or hot water, or a sulphur-dioxide solution (0.5–1 g/l) is kept in the new barrel before it is rinsed well. This washes out excess tannins that would make the spirit rough (Puškaš, 2011).
The key components of oak are lignin, tannins, cellulose and hemicellulose. The spirit extracts these and many others, gradually building its bouquet; oak gives not only colour but a whole range of compounds that improve taste and aroma. A mulberry barrel colours rakija yellow very quickly, but gives only colour, not the compounds that refine taste and aroma as oak does. Rakija meant to stay colourless must rest in vessels neutral to the distillate: glass demijohns, ash barrels, which give no colour, stainless steel or certain plastics that tolerate high alcohol.
Temperature and humidity
Rakija should be kept at 15–20 °C and a relative humidity of about 75%, without swings in temperature. To speed maturing it can be kept warmer for a while, which speeds up oxidation and the extraction of oak compounds. At lower humidity much rakija is lost to evaporation; at higher humidity alcohol and water do not evaporate evenly, which upsets proper maturing.
Physical changes
During maturing the colour changes, and the volume falls as the staves soak up spirit and some evaporates; the extract and the specific gravity rise, and the strength falls as alcohol evaporates. The colour change is the clearest: after 6 months the distillate turns golden yellow, sometimes golden brown, through oxidation and the breakdown of quercetin.
Chemical changes
Maturing begins with the extraction of phenolic compounds from the wood and their oxidation by oxygen from the air, which is why oak suits it: oxygen can pass through the staves. Copper acts as a catalyst of oxidation and an activator of oxygen, so it matters that the still is made of electrolytic copper, leaving the right minimal amount in the final distillate.
As rakija matures it draws tannins, hemicellulose, lignin and minerals from the oak; most are not volatile, so they concentrate in the finished rakija. Alcohol breaks down lignin into aromatic aldehydes that improve the aroma, and maturing brings oxidation of aldehydes and alcohols, esterification of higher alcohols into pleasantly fragrant esters, and acetalisation, which binds the unpleasant acetaldehyde with ethyl alcohol into pleasant-smelling compounds.
Losses
Losses come from spirit soaking into the staves and evaporating, and are greatest in the first year: up to 2% in the first two months, about 5% in the whole first year, about 3.5% in the second, and 1.5–2.5% a year after that. On average they come to 2–3% over 5 years in a 500-litre barrel. They fall with time as the spirit grows more viscous; in hermetically sealed vessels they are negligible even after a long time.
The loss depends on temperature and humidity, barrel size and the quality of the wood. It is greater in smaller barrels, at higher temperatures, in part-empty vessels, with stronger spirit, with strong ventilation and at lower humidity. Older barrels soak up less and let less evaporate. The average yearly loss of alcohol is about 1%. The loss also has an upside: the share of extract, and the relative density of the spirit, rise.
