Hydrolyzes chromogen 5-bromo-4-chloro-3-indolyl-beta-D-galactopyranoside (X-gal), o-nitrophenyl-beta-D-galactopyranoside (ONPG) and lactose. Hydrolysis of terminal non-reducing beta-D-galactose residues in beta-D-galactosides. Optimum pH is 5.0 with ONPG as substrate. Optimum temperature is 70 degrees Celsius with ONPG as substrate. Stable for several months at 4 or -20 degrees Celsius in the presence of 10% glycerol. Activity increases continuously from 30 to 90 degrees Celsius and drops dramatically at higher temperatures. Retains 50% of its initial activity after 1 hour incubation at 70 degrees Celsius. Retains 90% and 50% of activity after 30 minutes of incubation at 70 and 80 degrees Celsius, respectively. The residual activity of the enzyme decreases to an undetectable level after heating for 30 minutes at 90 degrees Celsius. The enzyme still maintains significant activity at 30 degrees Celsius. Belongs to the glycosyl hydrolase 42 family.