A product used to thicken milk when making custard, ice cream and cheese. Rennet tablets contain the natural coagulating enzyme, rennet. Rennet is used to curdle milk or separate curds from whey. When making custard, the rennet tablet is generally crushed and then dissolved in water before it is added to a lukewarm milk mixture. It is quickly stirred into the milk mixture and then allowed to stand for a short period of time in which it will quickly thicken the mixture into a smooth thickened custard.