Cleaves o-nitrophenyl-beta-D-galactopyranoside (ONPG) in vitro. Hydrolysis of terminal non-reducing beta-D-galactose residues in beta-D-galactosides. Requires 4 M NaCl or KCl for maximal activity. Optimum pH is 6.5 with ONPG as substrate. Measured at 37 degrees Celsius and in 4 M KCl. Optimum temperature is around 50-55 degrees Celsius in 4 M KCl and at pH 6.5. Partial activity (10-13% of maximum) at temperatures from 4-10 degrees Celsius. Belongs to the glycosyl hydrolase 42 family.