Lambic is a spontaneously fermenting beer brewed in the Pajottenland, a region in West Belgium, southwest of Brussels between the rivers of Dender and Zenne/Senne.
The ingredients of a lambic are approx. 60% light barley malt and approx. 40% light raw wheat, aged hops with little residual aroma, water, and local natural micro-organisms which initiate spontaneous fermentation. Lambic mash is made in a time and labour intensive mashing procedure called turbid mash. Turbid mash means that the wort produced contains non-converted starch as well as a high content of proteins which provide nutrients for the microorganisms during the long period of fermentation.
Lambic wort is boiled considerably longer than any conventional wort. After boiling, the lambic wort is cooled in a coolship for up to 12 hours and during this process infected with the microorganism prevalent in this area, a mixture of Brettanomyces, Saccharomyces, Pediococcus and others.

Then it is transferred to oak barrels for secondary fermentation and maturing. Spontaneous fermentation is currently only found in Belgium, and the designation of lambic is regionally restricted to the Pajottenland. However, today in Belgium brewers also make use of ready-to-use mixtures from yeast labs.

Lambic is sold under different designations, depending on its ageing: jonge lambiek/jeune lambic (young lambic) or oude lambiek/vieux lambic (old lambic). Young lambic is no older than one year and served only on special occasions in Brussels and in the Pajottenland. Old lambic, older than one year, is also available in bottled form. Lambic is a Presidia-member in the Slow Food Foundation of Biodiversity.

Lambic is a dry beer without residual sugar content, showcasing the fragrance of hay as well as earthy, animalistic-type flavours and whiffs of fruity aromas, as well as impressions of apples, citrus, rhubarb and honey. Lambic is also the basis for Geuze, fruit lambics and of the sweet variant of Faro.