What are lambic and gueuze?

Lambic is a Belgian beer of spontaneous fermentation. The wort contains at least 30 percent wheat and is not treated with cultured yeast, but with micro-organisms from the surroundings.

With ordinary beer the brewer adds a selected yeast culture and fermentation takes place in days. With lambic that does not happen. The brewer lets the wort be infected by whatever is present in the air and in the brewery, and fermentation then lasts months to years.

Lambic itself is still beer, without carbonation. It forms the base for gueuze, kriek and other lambic beers.

The boiled wort goes into a shallow open vat and cools there overnight. During that cooling, wild yeasts and bacteria from the air end up in the wort.

Researchers from Ghent University followed that process for two years and published their findings in PLOS ONE. They describe the coolship as the place where microbial growth begins, without any addition of starter cultures, and collected more than 2,000 bacterial and yeast isolates.

That work shows a fixed sequence: in the first month enterobacteria dominate, in months two and three Pediococcus damnosus and Saccharomyces take over, and from about month six Dekkera bruxellensis becomes the leading organism.

Gueuze is made by blending young and old lambic and letting that blend referment in the bottle. The young lambic still supplies fermentable sugars, so carbon dioxide forms in the bottle.

Stricter requirements apply to oude geuze. HORAL, the umbrella organisation of lambic brewers and geuze blenders, states that oude geuze consists of 100 percent old lambic from spontaneous fermentation, with a weighted average age of at least one year. The oldest component must have matured for at least three years in wooden casks.

The bottle then referments and, after six months of bottle ageing, must meet fixed analytical values.

Kriek is lambic to which cherries have been added. The fruit sugar restarts fermentation. In oude kriek it concerns 10 to 25 percent by weight of cherries, cherry juice or concentrated cherry juice.

The maturation is also laid down. According to HORAL, the lambic in oude kriek has a weighted average age of at least one year, with the oldest part at least one year in wooden casks, followed by re-fermentation and six months of maturation in bottle.

A European quality mark that protects a traditional method rather than a region. Oude geuze and oude kriek have been in that register since 1997 and must meet a fixed product specification.

Recognition came with Regulation (EEC) No 2301/97 of 20 November 1997. With Implementing Regulation (EU) 2017/2216 of 1 December 2017, the names were entered in the register again, including Oude Kriek, Oude Kriekenlambiek, Oude Frambozenlambiek, Oude Geuze, Oude Geuze-Lambiek and Oude Lambiek.

A bottle with the word oude on the label therefore follows a fixed recipe. Without that word those requirements do not apply.