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Heat-set stains

Heat does not remove some stains, it installs them. Three different mechanisms are involved, and they cover most of what comes out of a tumble dryer permanent.

In detail

Heat helps with a great deal of cleaning — it lowers the viscosity of fats and speeds most reactions — which makes it counter-intuitive that it is also the commonest way a removable mark becomes a permanent one. Three distinct mechanisms are at work and they affect different stains. PROTEIN DENATURATION: blood, milk, egg and gravy contain proteins that unfold irreversibly when heated and bond into the fibre, which is why the trade instruction for blood is cool water and why a protein mark that has been through a hot wash is finished. OXIDATION AND POLYMERISATION: oils, carotenoid pigments such as the lycopene in tomato, and sugars react faster at temperature, turning a soluble deposit into an insoluble one — this is what a tumble dryer does to a tomato mark that survived the wash. And FIBRE SWELLING AND SETTING: heat plus moisture allows the fibre itself to move and reset around whatever is in it. The single practical rule that follows is the most useful one in laundry: check before drying, never after. A dryer is the last chance to make an error irreversible, and the check costs seconds.

Why

Sources for this page

Sources

  1. Spot Solver: spot and spill removal procedures

    The Carpet and Rug Institute (CRI) · Trade or professional body

    Relied on for: That procedures for protein deposits use cool or lukewarm water and that heat is nowhere used to open a stain treatment in the database. (states this directly)

  2. Technical Bulletin ISP-1009: Guide to Improved Shrinkage Performance of Cotton Fabrics

    Cotton Incorporated · Trade or professional body

    Relied on for: That tumble drying is a dominant contributor to dimensional change in cotton fabrics. (background and mechanism only)

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