When it comes to the type of string to use, tying a pork roast is much the same as tying any other type of meat. String for culinary purposes is identified by several names, including cooking string, kitchen string and butcher's twine.
Pure and Simple
The important distinction for cooking string is its construction. Synthetic strings will typically melt in the oven, and the color in dyed string will leek into the food. Opt for genuine, pure cotton or linen string that is white or off-white. You do not want any plastic coating on the outside of the string. If you are unsure of the material, conduct a test with a lighted match. Synthetic string will melt and shrivel up, while cotton and linen simply smolders. Avoid jute string, as it is course and hard to work with when tying a pork roast.