working in a surgical area I am very well schooled on strict asepsis and am aware of how EASILY things can be cross-contaminated. Unless you don surgical gloves and everything you touch is sterile, there is no way to prevent the introduction of micro organisms into your product. I think the best we can do short of autoclaving everyting and "suiting up" for surgery, is to work on clean surfaces that have been cleaned with either a bleach/water mix or alcohol (at least 90 proof), have clean hands that have been scrubbed thoroughly with an antibacterial soap (for at least 3 mins and don't forget under the nails!) and that you use an effective and appropriate preservative to prevent things from growing.