Page:The story of milk.djvu/117

A measuring glass and an accurate thermometer are indispensable

The Marschall rennet test

bacteria to multiply in the milk until a Rennet Test^[1] or Acid Test^[2] shows that the desired degree of acidity has been reached. The starter may be sour whey or preferably prepared from sweet skim milk or whole milk with a commercial lactic acid culture as described in Chapter I under Ferments and Buttermilk. From 1% to

1. The Marschall Rennet Test consists of a graduated cup (a) with a fine hole for an outlet in the bottom. One cubic centimeter of a standard rennet extract is diluted with water in the glass bottle (c). The cup is filled with milk and placed on the corner of the cheese vat, the milk being allowed to run through the fine hole in the bottom of the cup. The moment the surface of the milk reaches the upper mark of the graduation in the cup the diluted rennet extract is added and quickly stirred into the milk with the spattle (d). When the milk begins to curdle it stops running out. The sweeter the milk is the more will run out before coagulation stops it and the mark on the scale at which it stops indicates the degree of acidity or ripening. The point is to have the milk alike every day and if, for instance, the cheesemaker has found that his cheese is best if he adds the rennet to the milk in the vat when the test shows 2-1/2, he wants to ripen the milk to that degree every day. So, if the test shows 3 or 4, it indicates that the milk is not sufficiently ripened and it should be allowed to stand warm for a longer time before it is set with rennet.
2. The Acidometer for making an Acid Test is described in Chapter I.