The process is similar to that of homebrewing wine. If done slowly, it requires rigorous hygiene and filtering of the product. If brewed fast, specialized dried yeasts are available in amounts to drive the fermentation process through before bacterial infiltration can take place, in about three days. In Finnish the latter are called pikahiiva (lit. quick-yeast), and they are sold in about a hundred gramme packs dry, as opposed to the live standard pack of brewer's yeast of 50g wet.
Properly made kilju is a clear, colorless or off-white liquid with no discernible taste other than that of ethanol. It can be produced by natural settling of the yeast over time, but nowadays various fining agents are used to hasten the process as well.
Kilju is often produced improperly by home brewers who allow contaminants to disrupt fermentation or do not adequately filter or rack the liquid, or do not use a fining agent. The latter mistakes result in yeast being suspended, causing the mixture to be cloudy rather than clear. The yeast is not harmful, but can yield an unpleasant taste and intestinal discomfort. It is also a common mistake to leave the carbon dioxide produced by fermentation into the suspension, so that the yeast provides it with nucleation sites, keeping the yeast up in the solution. Proper technique calls for airing the product after fermentation, stirring, and perhaps for fining agents such as microsilica or various semipolar proteinaceacous or carbohydrate agents.