De-bugging for quality

Some years ago multiple checks were carried out on the level of micro- organisms in many ready-to-eat foods and the incidence of listeria and other harmful pathogens was found to be unacceptably high.

The food industry had to put its house in order and this had an immediate knock-on effect for launderers and rental operators.

The food industry requires garments that are not only cleansed to a high standard but which create an excellent visual impression with staff and visitors alike. This means that not only must staining and soiling be removed but the garment must be delivered in a crease-free form.

Modern washing machinery and chemical processing means that perfect soil and stain removal need present few problems but many garment contractors are still failing because of unacceptable creasing levels. Far more difficult is ensuring that a garment is not only bug free but that it carries no residual nutrients capable of supporting bacteria.

The laundry engineer has much to offer when it comes to avoiding creasing of workwear garments. The washing machine itself needs to have a cage which is square or over square—that is the length of the cage should be as big or greater than the diameter.

The greater the cage capacity the more important this is to prevent the pressure of a wet garment load causing excessive creasing to the garment at the bottom.

The lifters around the cage must have a steep and large cross section to get a firm hold of the work load and to lift it to the 11 o’clock position, where it can fall back across the cage diameter with the normal rubbing, twisting and pounding motion.

For this to work properly the ‘G’ factor in the wash must correspond with the lifter design. At ‘G’ factors below 0.7 there is a tendency for the work to fall away at the 9 o’clock position, roll over and create long roping creases in arms and legs.

At ‘G’ factors higher than 0.8 the opposite tends to occur—the work stays fixed to the outside of the cage for too long and fails to break away and use the full cross-sectional area of the machine.

The water level in the machine must be sufficient to give adequate buoyancy to the garments at the base and it must also provide a cushioning effect for garments tumbling across the cage diameter.

That is why wash dips in garment processing are generally higher than those in flatwork processing. If high wash temperatures are needed then it is essential that the work is cooled down slowly, traditionally at a rate no greater than 4°C per minute.

Workwear garments require as much care in rinsing to avoid the normal problems of galling and odours. It is always tempting to program an interspin after each rinse to improve rinse efficiency but this will only succeed at a temperature below 45°C and even then the spin speed and spin time should be limited. One minute at low speed should be quite sufficient to raise the rinse efficiency.

At the end of the cycle the machine needs to be unloaded properly—the longer the load stays pressing down on garments at the bottom either in the machine or in the barrow, the greater will be the pressure creasing.

Weighed down

When the garment enters the tunnel finisher it passes through a steam spray. Most units have no way of monitoring or setting the steam flow rate other than trial and error but it is vital to get the garment warmed up quickly and to keep the humidity in the initial relaxation zone very high. The garment needs to be weighed down by the water saturating it at high temperature for as long as possible for the first stage of crease removal to be effective.

After this the garment starts to dry and the rate of drying is determined by the humidity of the circulating air and the air velocity. The objective is often not to rapidly dye every garment but to use the smoothing effect of the downward air flow to remove creasing whilst recycling air to maintain a high humidity so that crease removal occurs before the drying process brings it to a halt.

Total removal of soiling and staining is a requirement for most food industry customers and requires high temperature, high mechanical action and plenty of emulsification power within the detergent system.

Vegetable dye stains can be de-coloured using an appropriate bleach—they do not have to be washed out. Every other type of soiling, however, needs to be removed from the fibres and kept in suspension in the wash liquor until it can be flushed safely down the drain.

If suspension power of the wash process is inadequate then soiling will re-deposit onto the cloth causing greying and also leaving nutrients for bugs.

Most garments are bug free when they come out of the tunnel finisher because few bugs can survive twenty minutes in circulating air flow above 140°C.

The real problems arise if bugs survive in a damp seam, where they can breed and multiply on the way to the customer’s plant. When this occurs it is frequently accompanied by unpleasant odours.

To minimise this risk, not only must the wash process be sufficient to take out obvious soiling and staining but, importantly, it must also leave the individual yarns free of any nutrient that might help to support microbial growth.

So how can a launderer processing food industry workwear check the level of bugs on the cloth surface either immediately after processing or twenty-four hours later? One simple technique is to use a dip slide set up to provide an indication of the total number of viable organisms growing on the fabric surface. This consists of a lollipop enclosed in a small sterile perspex tube. One side of the lollipop is coated with blood agar and the other with a malt nutrient. Any bacteria creates colonies on one side whilst fungi prefer the other.

After forty-eight hours and seven days a quick count of the number of colonies on each side gives a good indication of the adequacy of the wash process in achieving a satisfactory bug kill. The method may not be acceptable to the micro biologist but it does provide a rapid, cheap, self analytical tool for the laundry manager.