Yard-stick of detection in Snyder's test is:
Acid formation
pH change
Count of microorganisms
Enamel solubility
Snyder's test uses Bromocresol green as an indicator, which is blue-green at pH 5.4 or above and turns yellow at pH 3.8 or less. 
The "critical pH" for enamel dissolution is 5.4-5.5.
Therefore, it would be more appropriate to use an indicator such as Bromocresol purple, which is purple at pH 6.8 and yellow at pH 5.2.

Soben Peter 5th edition
Page number  434