Weight and Pressure
If you walk on fresh snow you will probably sink in. If you put on big wide snow shoes you won’t. The difference is that the snow shoes spread your weight over a larger area and that puts less pressure on the snow. What does this have to do with making cheese?
If you press the cheese in a small diameter cheese mold with 50 lbs, the effect on the cheese is different than if your cheese mold has a larger diameter and you press with the same 50 lbs. The larger cheese mold will have less pressure because the weight is spread over a larger area.
When pressing cheese the goal is to press with accurate pressure. There are many variables in making cheese but this will eliminate one of them.
Weight is measured in pounds ( lbs ). Pressure is measured in pounds per square inch ( PSI ).
The pressure is the weight you put on one square inch of area. So if the area of the top of your cheese mold is 9 square inches you will have to put 9 pounds of pressing weight on the cheese mold to get 1 PSI. That is 1 pound on each of the 9 square inches of area which is 1 pound per square inch.
The formula is pressure = weight / area
Cheese making recipes use different units of pressure, pounds per square inch, kilograms per square centimeter, or kilo-pascal.
Here is a pressure conversion calculator
How much Pressure
How much pressure do you need to make cheese? That is not an easy question because there are so many variables in making cheese.
The easy answer is that if your cheese doesn’t have a good knit to its texture, use more pressure, but the range is from 0 to 20 Psi. The knit of your cheese is also dependent on the temperature of the curds while you are pressing.
As an example, to get 4 PSI on a 4 1/2 inch diameter cheese mold requires 64 lbs pressing weight. To get 15 PSI on the same mold requires 239 lbs. To look at other pressures here is the press calculator.
Here are some links to discussions on the amount of pressure for different types of cheese.
Cheese Forum pressure discussion