Adding dairy products like milk or cream before pressure cooking is generally not recommended, as they can curdle, separate, or scorch at high temperatures and pressures. It's best to add them after pressure cooking is complete.
Pressure cookers work by creating a high-pressure, high-temperature environment. This environment can cause significant changes in dairy products. Milk and cream contain proteins and fats that are sensitive to heat. Under pressure, these components can coagulate, leading to curdling or separation. Furthermore, the sugars in milk can caramelize and potentially burn or scorch on the bottom of the pressure cooker, affecting the flavor of the entire dish and making cleanup difficult. To avoid these issues, it's best to add dairy after the pressure cooking process, once the pressure has been released and the temperature has cooled down slightly. This allows the dairy to blend smoothly into the dish without the risk of curdling or scorching. You can gently stir in the milk or cream and heat it through on a low setting.
If a recipe calls for a small amount of dairy, consider using a stabilized dairy product like evaporated milk or a small amount of cream cheese, as they are less likely to curdle. However, even with these, add them after pressure cooking whenever possible.