Naturally and spontaneously fermented beers with high to very high levels of esters, plus bacterial and yeast-derived sourness that sometimes includes acetic flavors. Lambics are not blended, while the gueuze style blends old and new lambics which are re-fermented in the bottle. Historically, they are dry and completely attenuated, exhibiting no residual sweetness either from malt, sugar or artificial sweeteners. Sweet versions may be created through the addition of sugars or artificial sweeteners. Many examples of this style are made to resemble the gueuze lambic beers of the Brussels area, where it originated.