=Refermentation in the bottle=
[[File:BrasserieCantillon-18.jpg|thumb|right|Lambic fermenting in the bottle at Cantillon]]
Gueuze and other lambic bottled with either some residual sugar left unfermented at the time of bottling or added priming sugars will undergo significant fermentation in the bottle, though all unpasteurized lambic will continue to ferment to some degree there. For lambic bottled after about 8 months without additional sugar, the fermentation in the bottle progresses much as an extension of the Brettanomyces stage of fermentation and negligible carbon dioxide and ethanol production occurrs, leaving most of this lambic still. For lambic bottled younger and those with additional fermentable sugars added at bottling, considerable fermentation by Saccharomyces occurs in the bottle, causing marked increases in ethanol and the production of carbon dioxide, leading to a carbonated product.<ref name=Oevelen77 >D. Van Oevelen, M. Spaepen, P. Timmermans and H. Verachtert, [http://onlinelibrary.wiley.com/doi/10.1002/j.2050-0416.1977.tb03825.x/abstract|MICROBIOLOGICAL ASPECTS OF SPONTANEOUS WORT FERMENTATION IN THE PRODUCTION OF LAMBIC AND GUEUZE], 1977</ref>