Although beer refermentation in bottles is essentially a simple process, mixing mature beer with yeast and sugar before bottling, refermentation is often difficult to control in industrial practice. This can result in variable batch-to-batch quality, especially in small-scale breweries. In this study, industrial top-fermented beers were mixed with freshly propagated yeast and fermentable extract. The extract consisted of glucose, fructose, maltose, sucrose, or one of several commercially available sugar syrups. Glucose, fructose, and sucrose were fermented at comparable rates, reaching final attenuation within two weeks. Maltose was only partially fermented or not fermented at all, depending mainly on the yeast strain used. Several factors that may affect sugar uptake were examined. Carbon dioxide pressure in the bottled beer accounted for most of the loss in the capacity of the yeast to ferment maltose, while it had only a minor influence on the uptake of glucose and fructose. This difference is probably due to the different mechanisms by which these sugars are transported into the cell. Although maltose is the main sugar in brewing wort, its use is not appropriate for bottle refermentation. The use of sugar syrups with high maltose content may lead to irreproducible or stuck fermentations. Moreover, residual extract promotes inconsistent yeast deposit stability.