I used to work in a 3 rosette kitchen some years ago, and we used to use muslin 2-3 times a day for straining various things (stocks, jus, soup, etc). We always just soaked the muslin in warm soapy water for about 20 minutes immediately after use, then got our hands in the sink and gave it a good swirl and swill. Never had any problems with it, and that was using the same cloths again and again in a food environment. For my hop bags i just do this, then ring them out and rinse them, and boil them in water before next use.