CHEM CLASS
'(<a href="http://www.j-archive.com/media/2007-02-05_J_22.jpg" target="_blank">Cheryl of the Clue Crew gives the clue in front of a flask and beaker.</a>)  Milk has its solids distributed throughout the liquid; to clump the solids into curd, I've <a href="http://www.j-archive.com/media/2007-02-05_J_22a.jpg" target="_blank">added vinegar</a>, a weak one of these'
an acid