Alkaline Ester Hydrolysis Reaction
Alkaline hydrolysis of ester:


  $\ce{RCOOR' + OH- -&gt; RCOO- + R'OH}$


Almost all organic acids are weak acids:


  $\ce{RCOO- + H2O &lt;&lt;=&gt; RCOOH + OH-}$


Therefore, a lot of $\ce{OH-}$ is consumed during the esterification, with the product $\ce{RCOO-}$ generating little $\ce{OH-}$.

There is a net consumption of $\ce{OH-}$, making the solution more acidic, lowering the pH.