The hydrolysis of Tween 20 (lauric acid ester),
Tween 40 (palmitic acid ester), Tween 60 (stearic
acid ester) and Tween 80 (oleic acid ester) was
tested on Tween agar plates [ 151. As a result of
the hydrolysis of esters, calcium salts of the fatty
acids thus produced became visible on the plates
within 24 h at 37 "C. The esterase-positive strains
were streaked out on a new plate and the reaction
was declared positive if both plates gave a positive
result.