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I was making pie dough the other day and while preparing the dough a common term used in baking, cut in, jumped out at me. I realized how confusing this term must be to novice cooks and especially to non-native English speakers. It’s actually a phrasal verb and is idiomatic: to cut in or ‘cutting in.’ This has a meaning in cooking and a definition outside of cooking. What is the definition of cut in when used in cooking?
It doesn’t mean to cut into something with a knife. Instead, it is a mixing method used to incorporate butter or shortening into dry flour. To do this a pastry blender, or as it’s often called, a pastry cutter is used (also called a dough cutter).
A pastry blender looks sort of like an old-fashioned sword guard except sharp. It is a rounded loop of metal that separates into blades or heavy wires on one side and a handle on the other.
When making pie dough and similar pastries, as well as some cookies, it is best to keep the dough as cold as possible while working with it. For recipes that call for vegetable shortening or lard, this is not as necessary as these ingredients have a higher range of plasticity in warm temperatures.

How To Cut In Butter
To cut in butter, the flour is put into a medium or large bowl and the butter is cut into small pieces and tossed together with the flour.
Then a pastry blender is used to press down on the butter pieces and into the flour, over and over, until the butter gets cut into finer and finer pea-like and then bread-crumb-like pieces which all become coated with flour.
For this to work properly the butter must be cold and firm. After all the butter has become small crumbs and is thoroughly mixed with the flour, it can be formed into a dough. Sometimes, according to the recipe, liquid ingredients are added. When making pie crust, ice water is added. When making biscuits, milk or buttermilk is added.
When the resulting dough is cooked, the small pieces of fat are still solid, surrounded by flour. When they heat and then melt, this results in flaky layers. If the butter was allowed to soften and was mixed in thoroughly a denser and tougher baked product would result.
Note that this article is meant to serve as an explanation of the term ‘cut in’ or ‘cutting in.’ It is not a recipe for pie dough. I am not a pie-making champion. I do try, though. You can learn more by viewing the video below.
By the way, if you were wondering when used outside of cooking, ‘to cut in’ means to replace someone as a dance partner or to insert yourself into a line of waiting people instead of going to the end of the line.