To cook oxtails in a Crock-Pot or slow cooker, first season and brown them in a skillet. Add the browned oxtails to the slow cooker along with a liquid of your choice, such as beef broth, wine or water. Cover the slow cooker, and cook the oxtails for five to six hours on high or 10 hours on low.
- Season the oxtails
Season the oxtail pieces generously with salt, pepper and other spices of your choice, such as minced garlic, minced ginger, onion powder and cayenne pepper. You can also season them with fresh or dried herbs such as thyme, rosemary and basil.
- Brown the oxtails
Coat a heavy-bottomed skillet with vegetable or canola oil, and place it over medium-high heat. Add the oxtails to the hot oil, and turn them over continuously using tongs until they are browned all over.
- Add oxtails to the Crock-Pot
Place the oxtails into the slow cooker insert. You can also add in additional ingredients if you prefer, such as sautéed onions, carrots, celery or peppers.
- Add liquid to the Crock-Pot
Pour in enough liquid to fully cover the oxtails in the slow cooker. You can use beef stock, red wine, beer, water or a combination of liquids. You can include flavoring liquids such as fish sauce, soy sauce and vinegar, as well as tomato paste.
- Set the Crock-Pot
Cover the slow cooker with its lid, then set it to cook on high for six hours or low for 10 hours. If the oxtails are not tender enough after the allotted time, continue cooking them until they are tender enough for your taste.