oak essences or , usually illegal winemaking additive (unlike oak chips) which can inexpensively substitute, at least in the short term, for some of the oak flavour imparted by barrel maturation in expensive new oak. Various powders and liquids are marketed based on extractions from different woods. In some cases, specific tannins are targeted and extracted so as to add structure as well as flavour to a wine (see oenological tannins).
Doses of powdered oak extracts can vary between 5 and 20 g/hl but powders are more difficult to use than liquids because of potential problems with clarification. The usual dose of a liquid extract is about 0.01% and, since most liquids are based on ethanol or brandy, they can be extremely difficult to detect analytically. However, their ability to sustain a wine through bottle ageing is questionable.