Porcini mushrooms can be preserved through various methods to extend their culinary use. Freezing is a popular option – clean and slice the mushrooms before freezing for up to six months. Alternatively, you can preserve porcini mushrooms in brine in a jar. This involves packing cleaned mushrooms in a solution of water, salt, and sometimes vinegar. Lastly, drying porcini mushrooms is a traditional method, ensuring a longer shelf life. Once dried, they can be rehydrated for use in soups, stews, and sauces.