Are there any health risks when making vegetable stock from kitchen leftovers?
Simple washing (for carrots, or veg. you might peel) is fine, if you don't want to peel.  There is no problem using root vegetables without peeling either.  Stocks are typically brought to a simmer.  So, you easily mitigate any bacterial concerns.  Botulism toxins form in an anaerobic environment.  So, you don't really have to worry about using fresh, even unpeeled, root vegetables.   Of course, you need to adhere to general food safety, and have an awareness of &quot;the danger zone.&quot;  So your stock needs to at least cook above 140F (60C), and then be cooled below 40F (4C) with two hours of completion.