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How On-premise Laundries Cope With Stains
from meat juices to marking ink to pepper particles and copy machine toner

By Nathan Schiff, PhD
Associate Editor - Institutional

Meat processing plants often use On Premise Laundry (OPL) facilities to wash their smocks and garments. This is the story of one such plant, using two 20 lb and one 35 lb Wascomat machines; operating 3 laundry shifts a day.

Meat Processing Plant

The company purchases uncooked turkey and ham meats from their supplier and incorporates them into finished products. Essentially, the meats are placed into a mould and are then either cooked or smoked.

Nature of Stains

Meat juices make difficult-to-remove stains on the clothing provided to workers by the company. These juices are very high in protein, but have little blood in them The challenge becomes one of effectively removing significant amounts of protein stains without coagulating the stains onto the surfaces or within the fibres of the garment. Similar type of stains may also be a problem in some of the exclusive restaurants which prepare specialty meat products.

A second problem stain to remove is a result of pickling mixtures, containing very fine particles of cracked black pepper being transferred to the garments. Because of their small size, these particles bind tenaciously to the fabric's fibres and are difficult to dislodge.

Removal Procedure

Initially, this company used a single powder laundry product, but has subsequently switched to three liquid products, which are accurately dispensed by a three-pump system. This provides better cost control and also better stain removal.

Essentially, their operation is as follows: The garments are pre-rinsed with cold-to-luke-warm water, in order to drain off as much as possible of the loosely bonded, meat fluids. Using a high temperature pre-rinse would be detrimental to the cleaning process. Heat coagulates proteins in a manner similar to what happens when an egg is cooked in hot water. In a laundry process, coagulated protein sets onto and within the fibres, resulting in a more difficult stain to remove.

Following rinsing, a liquid surfactant blend and alkaline additive are precisely metered into the washer via two calibrated, peristaltic pumps. The garments are then washed for 20 minutes at 140º F.

The final step includes a precise dose of hypochlorite bleach using twice the amount normally used for bleaching white garments.

Chemistry of the Stain Removal

With the proper blend of surfactants, the detergent portion of the wash formula emulsifies the protein. Protein breakdown then occurs in solution and in the presence of the added alkali The amount of alkali required depends on the soil load and the fabric being cleaned. This can range from 300 to 3000 ppm alkalinity, expressed as Na2O.

High concentrations of polymers are also incorporated into the surfactant blend, in order to dislodge the fine pepper particles. These specialty polymers have a greater affinity for the pepper particles and compete with the fibres for them. The resulting pepper-polymer complex so formed, is then kept in suspension by the blend of surfactants.

Poultry Slaughtering Plant
The problem stains encountered in this plant, were mainly due to the inks which are used for day code package markings being transferred to the garments. A secondary problem resulted from blood staining.

Stains from Packaging inks
Food marking or packaging inks are derived from either dyes or pigments. Removal of dyes which don't respond well to hypochlorite bleaching (oxidation) are treated with reducing agents. This converts them to their colourless or leuco form. The reducing process takes approximately 20 minutes for completion, using either sodium hydrosulfite or sodium bisulfite. Other specialty reducing agents include sodium bisulfite, potassium permanganate or titanium chloride.

Pigmented inks on the other hand, contain extremely fine solid particles, such as carbon black, which are suspended in a solvent system, allowing them to dry quickly. They are similar in composition to the toners used in photocopy and fax machines or in computer printer cartridges.

Because of their very fine size, pigmented inks adhere to fabric fibres more tenaciously than cracked black pepper. Their removal often requires the use of cationic surfactants, capable of neutralizing the electrostatic charges which bind them to surfaces. Surfactants alone cannot release these particles, neither can the conventional polymers which are used in removing black pepper. Some companies have attempted to use fabric softeners as their source of cationic surfactants. However, fabric softeners (one category of cationic surfactants), are poor stain removers. They also tend to waterproof the garments, contrary to their intended use.

Poultry Blood Stains
Blood stains ( containing protein and iron), lend themselves well to the techniques used in removing meat juice stains. However, it is not advisable to use chlorine to bleach out any residual iron, as this will fix the stain. An acid sour, such as hydrofluosilicic acid, is commonly used in the final rinse cycle. This both neutralizes residual alkalinity and removes iron by
sequestering it from the garment.

I would like to thank Joe Poppe, of AFCO Inc., Frazer, PA, a manufacturer and major supplier of Food and Beverage Hygiene systems and chemicals, for the field information which was provided for this article.


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