In a large skillet, heat the oil. Season the trimmings with salt and pepper and brown in the hot oil. Remove to slow cooker.
Fry onion in drippings in the pan until brown. Remove onion to slow cooker.
Deglaze the pan with the beer, scraping up any brown bits.
Add this liquid to the slow cooker along with all the other ingredients. Cook on low all day.
Strain the stock. Discard solids. Adjust seasonings. Allow stock to cool slightly before refrigerating. After refrigeration, any fat will rise to the top. Remove this and discard.
Use stock in recipe or freeze for later use.
Notes
Nutritional values are approximate and are based on ⅛ of the recipe. Refrigerate leftovers promptly and use within 4 days.