Product Safety Device
Maintenance Is Critical
There is no doubt that product safety devices (PSDs) have helped make the food and beverage industry safer. De-
vices such as sifters, strainers, mag-
nets and foreign-matter detectors have
been used for many years to remove
quency of checks should be determined
by how much product the facility is willing to put at risk. A replacement screen
should always be kept on hand to prevent unnecessary downtime in case one
of these devices becomes damaged.
If sifters or strainers are used for bulk
unloading, they should be checked after
each unload. This provides two benefits.
First, if foreign matter is found, the supplier or transport company can be held
accountable. Second, if a damaged
screen is found, the amount of product
at risk is reduced.
foreign matter from product streams. However, none of these devices
can be installed and then forgotten about and expected to continue
working properly. All of them need some level of maintenance to
keep them in good operating condition.
Sifters/Strainers
Sifters and strainers are used to filter foreign material out of a product stream.
Sifters are for dry ingredients and may have some type of shaker or vibration mechanism to keep product flowing. Strainers are used on liquids and do not typically
need anything more than the normal flow to function. These devices work basically the same way—product is passed through a mesh screen of a certain size to remove particles larger than the mesh. They have to be designed for the product type
and flow rate, and should use a mesh slightly larger than the product particle size.
Systems may be designed with several devices of different sizes that serve different
purposes.
As an example, a mill will typically have a coarser-mesh sifter early in the
process to pull out larger foreign matter, such as stalks, rocks and other field-related
items, primarily to protect the equipment that will later grind the grain into smaller
particles. A much smaller mesh usually will be used right before packaging to ensure that there is no foreign matter in the final product.
Sifters and strainers need relatively little maintenance. They must be checked periodically to ensure that they are undamaged and properly in place. These checks
should be documented with the date and time. Any damage or evidence that they
are not seated properly means that something may have passed through that was
not intended. Follow-up on the product that was produced since the last good
check should be conducted to ensure that there is no contamination. The fre-
Magnets
Magnets are used in different parts of
the process for similar reasons as sifters
and strainers. Unlike sifters and strainers, however, magnets will remove only
ferrous metal, not other foreign material.
They need a little more attention and
care than sifters and strainers. Their design, strength, type and size are dependent on several factors:
Product type. A thick, viscous product
will require a stronger magnet than a
lightweight, free-flowing product.
Flow rate of the product. The magnet
must be able to capture and hold the
metal against the flow of the product. It
is harder for a magnet to remove and retain metal from a fast-moving product
than a slower-moving one.
Amount of metal that is expected to be
captured between checks. If the amount of
metal expected is high (e.g., grain from a
field is expected to have more metal
than flour), then the magnet’s holding
power will need to be higher. If checks
will not be done frequently, a stronger
magnet may be needed to account for
this. If the magnet is overwhelmed with
metal, some either will not be pulled
out, or will get knocked loose by the
product flow.
Once a magnet has been installed, it
must also be checked and cleaned periodically, and these checks should be
documented. Care is needed during
cleaning to ensure the magnet is not
damaged. Since the magnets themselves
are usually brittle (they are typically en-
