Yes, you can transfer everything in the slow cooker and cook for more than an hour and 20 minutes. Once the beef is tender it's done; depending on the cut that you are using it may take less or more than the time in the recipe. Tenderloin cooks faster! Mirin is a cooking sweet rice wine, it is not vinegar and shouldn't be confused with one another. You can omit it and use sugar, Sake or any other Rice wines if you desire. For less spicy, use less Korean Chili Pepper paste and of course look at the number on the gochujang package...I used #3 which is medium spicy, really mild taste, but you can go higher for spicier.