Why It's Safe To Put Raw Beef Straight Into The Slow Cooker - Tasting Table
Briefly

The key to safely slow cooking raw beef, as with any dish, is ensuring it is fully cooked before you eat it. This means reaching an internal temperature of 160 degrees Fahrenheit for ground beef and at least 145 degrees for all other cuts. Most slow cookers heat to a minimum of 170 degrees, so if you allow ample time, your beef will have no issue reaching a safe temperature.
Preheating your slow cooker is a great idea when using raw beef, as a pre-warmed container will ensure that the meat exits the danger zone with ease. Don't forget to keep the lid on while cooking, especially at the beginning, so that the heat stays in and your meal cooks evenly. That longer cooking time is the key to making sure that your raw beef reaches a safe temperature for eating.
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