Catalyzes the 2,6-dichlorophenolindophenol-dependent cleavage of acetoin into acetate and acetaldehyde. The alpha subunit is probably the catalytic subunit of the enzyme (By similarity). Ketone degradation; acetoin degradation. Tetramer of 2 alpha and 2 beta subunits. Strongly induced by acetoin. Transcriptionally up-regulated by AcoR and sigma-L factor. Subject to catabolite repression by glucose, in a CcpA-independent manner. Cells lacking this gene are unable to utilize acetoin as carbon source.