Shortening is a process that provides textures that most people find desirable in food such as crispness, shortness, light, crunchy and crumbly. In this post I will cover What is shortening? How do we do it? Why does it work? Where would we use it?
What is shortening?
Shortening is the combination of fat with flour used to make pastry or biscuits. The proportions of fat are usually half that of the flour for example 100g baking fat to 200g flour as in shortcrust pastry. The technique used to combine the fat into the flour is the rubbing-in method. When learning to cook this is done by hand but it can also be carried out in a food processor. Understanding the process is key to learning about the function of ingredients and how they work together.
How do we do it?
Rubbing fat into the flour means each grain of flour will be coated in fat. This coating makes the flour grain waterproof. Why does that matter? Waterproofing the flour grains means that when making pastry and therefore adding water to make the pastry dough the water does not soak into the flour grains quickly and therefore does NOT allow gluten to form. It is gluten that makes a strong framework in floury products such as bread. In bread we want gluten, so we knead the dough to work it and make it elastic. In shortcrust pastry we do not want a tough framework, we want crumbly and ‘short’. The word ‘short’ refers to the gluten formation, in rubbed in shortcrust pastry it will form short strands only. In bread gluten will form longer, stronger strands because we knead the dough. Learning to make pastry is all about handling the dough gently, not stretching it and giving it time to ‘relax’ to make it perfect. Shortcrust pastry requires skill and understanding to make it correctly.
Why does shortening work?
Using half fat to flour the recipe for means it is possible to use your fingertips to rub the fat into the flour. The dough is shortened because the flour grains are waterproofed, and this prevents the development of strong gluten. Mixing in the water to make the dough with a knife blade also reduces the amount of gluten formed.
All these things make sure the dough is ‘short’. In the oven when the dough is cooked at about 200⁰C, the water turns to steam, the fat melts and is absorbed by the flour grains to give flavour and colour to the pastry. The heat causes changes in the starch contained in the flour so that it browns (dextrinization). The short gluten strands are set by the heat so that the pastry changes from pliable to rigid. The resulting pastry is crumbly and melts in the mouth, a classic shortcrust pastry.
The rubbing-in method is a basic to learn, and it relies on the plasticity of fat to coat the flour grains as you prepare the recipe. Plasticity is the ability of fat to melt over a range of temperature. Yellow block baking fat is best to use and leaving it out of the refrigerator for a little while before rubbing-in helps it to perform best. The proportion of fat is important as it changes the texture and flavour profile of the end product. The image below shows experiments with different fat combinations.
Where would we use it?
The rubbing-in method that keeps products short is used for shortcrust pastry, shortbread, biscuits, cakes with half fat to flour such as Rock cakes, Raspberry buns, scones, crumble topping and similar recipes. The picture shows shortcrust pastry used for quiche.
I hope you now understand more about shortening and the rubbing-in method.