Conquering a critical control point

Prepared Foods, Oct, 1996 by Judy Rice

Mid-America Dairymen's Zumbrota, Minn., facility processes 1,300,000 pounds of milk per day into cheddar Colby, Monterey Jack and whey products. Like all of the dairy cooperative's plants, Zumbrota practices strict quality control and HACCP procedures.

One critical control point is the packaging area where shredded cheese is run through conveyorized Safeline metal detection units before and after packaging to ensure no metal shavings or particles have found their way into the product. Powdered cheeses are run through metal detectors after packaging in kraft paper bags.

"Our company policy is to stick with a specific supplier unless and until we can find somebody who does it better," says Andy Coffey, plant manager. "In the case of metal detection, we've been sticking with Safeline for quite some time because we haven't found anybody who does it better."

Mid-America has four metal detectors positioned near the end of the production line to examine products before they are boxed for shipment. The size/weight of the packaged products depends upon the order being run at the time and the customer requirements involved. The metal detector apertures are sized to accommodate Mid-America's largest product sizes, while still allowing for inspection of smaller sizes.

As Coffey points out, "The Safeline detectors can accommodate any line speed we run, and they deliver a high degree of accuracy that we're comfortable with. And whenever we have a question, Safeline staffers give us good, prompt service."

Inspecting cheese and other highly conductive products is especially difficult for a metal detector--particularly in the detection of stainless steel. Coffey notes that even greater precision on stainless steel detection would be a great benefit for the entire food industry because of the predominance of stainless steel equipment in the industry. This area has been the focus of extensive research work by Safeline over recent years and has resulted in the supplier's new Series 800 multi-frequency detector (see new unit at Safeline's Booth E-3173).

As Safeline President Andrew Lock explains, all metals fall into three categories: ferrous, non-ferrous, and stainless steel. Notes Lock, "The ease of detection depends upon their magnetic permeability (that is, how easily they are magnetized) and their electrical conductivity."

Ferrous contamination is most easily detected because it is both magnetic and a good electrical conductor. Nonferrous metals such as copper, lead, and aluminum, are non-magnetic. They are, however, good electrical conductors, and therefore generally easy to detect.

Stainless steel presents a more difficult challenge. Lock explains, "Stainless steel comes in many different grades--some magnetic and some austenitic (totally non-magnetic). Also, the conductivity of stainless steel is variable. To further complicate the situation, the problem of detecting stainless steel is amplified when inspecting wet or salty products."

Andy Coffey describes the metal detectors as "an integral part of the company's quality control, HACCP and vendor certification programs." An essential element of quality management involves setting standards and then ensuring that those standards are adhered to and documented. A special feature--Performance Validation Routine--of the metal detector ensures that this is done.

"Our customers demand metal-free guarantees, so we make sure we're prepared with documented evidence of our tests," declares Coffey.