Carpet dries from the tips. Therefore, as the cleaning solution evaporates from the tips, the water rises to the surface bringing with it everything dissolved in it, and then the water evaporates leaving everything else behind as illustrated above. This leaves on the tips of the carpet, rug or upholstery soil and high-alkalinity residue plus anything else left in the carpet such as high shampoo levels, cola, coffee, etc. This upward flow of moisture on fiber surfaces during drying is referred to as wicking. The factors contributing to browning are slow drying, over wetting, high alkalinity, BHT, and cellulosic material (jute backing).
In the beginning of this industry, most detergents used were nothing more than glorified concrete floor cleaners, which are highly alkaline and frequently caused browning. Carpets and carpet backings were not as good then either. Equipment now does a better job of leaving the carpet dry. Most carpet-cleaning professionals are now better trained and most (but not all) know better than to over wet a carpet or to use overly strong detergent solutions. Also, the carpet manufacturers now rarely use jute backing.
Cellulose browning occurs in natural fiber carpets like jute, wool, sisal, cotton and can also happen in some old carpeting when jute backing was used.
How to Cure Carpet Browning?
An application of a formulated organic acid agent such as Brown Out® will neutralize this residue not only preventing browning, but actually leaves the carpet cleaner and brighter. Additionally, the use of Brown Out on wet-cleaned upholstery and rugs will reduce the likelihood of dye bleeding by setting the dyes. It is easier to correct browning on carpet with pile yarns made of synthetic fibers than of natural fibers such as wool, hemp, silk or cotton. In cases where severe browning may occur, clean the carpet with Natural Fiber Cleaner.