Drying Pallets and Keeping Them Dry Help Prevent Mold from Occurring

[Guest guest]

Drying Pallets and Keeping Them Dry Help Prevent Mold from

Occurring: Fan Sheds, Chemical Dip Treatments Effective Combination

for Controlling Mold

Pallet Enterprise - Ashland,VA*

By Hamner

Date Posted: 8/1/2007

http://www.palletenterprise.com/articledatabase/view.asp?

articleID=2393

(Note: The Virginia Tech Center for Unit Load Design and the U.S.

Forest Service Wood Education & Resource Center (WERC) cosponsored a

conference in June on preventing and eliminating mold on wood

pallets. The conference offered a consolidated and comprehensive

educational curriculum. It was designed to teach primarily Eastern

hardwood lumber and pallet manufacturers and their customers about

mold-related problems, the causes of mold growth on raw wood

surfaces, and how to prevent and eliminate it. The conference

included topics relating to the science of mold, how mold affects

food processors, various chemical treatments for mold, pallet

drying, and a case study. Exhibitors from chemical treatment and

drying and heat-treating sectors were represented. The following

article summarizes the scope and content of the information that was

presented at the conference.)

Mold growing on newly manufactured wood pallets is becoming less

tolerated by many customers. Increasingly they are sending back

trailer-loads of pallets that have mold growing on them and

demanding mold-free pallets.

Unlike wood rotting fungi, molds occur only on the surface of

wood and do not damage its structural integrity. So, why all the

fuss?

The reasons are simple:

1) Mold growing on pallets can contaminate or discolor the

packaging and, ultimately, the product placed on them.

2) Mold on pallets can contaminate the workplace, directly or

indirectly contaminate product, and pose a health risk to people

working in the same environment.

3) Moldy pallets present an ugly, unprofessional appearance that

contaminates the packaged appeal of the finished unit load that is

ready for distribution.

Whatever the reasons, it is clear that mold on pallets is a

problem that is not going away.

Unfortunately, there is no `silver bullet' to remedy the

situation. However, with a little understanding and insight into the

nature of this beast and a thorough commitment from management to

develop and implement a comprehensive mold prevention strategy, mold

can be substantially minimized.

The Science of Mold

According to Dr. Jon Eisenback, plant pathologist at Virginia

Tech, microscopic mold spores are everywhere in the air all the

time — as many as 10,000 per cubic yard. There are thousands of

different species of molds that produce a variety of mold

colorations: blue, black, green, yellow, orange, red — you name it.

Mold spores are constantly floating around and settling onto wood

and other surfaces. Under optimal conditions, these spores will

germinate within 24 to 48 hours. Growth requirements for fungal

molds include oxygen, a food source, water, and warmth.

For wood, this means wood surfaces above 20% moisture content,

air temperatures between 60-90 degrees, and little to no air

movement. Mold spores can germinate and grow at lower temperatures

that are still above freezing — for example, in the winter when

pallets are stored indoors with poor ventilation and at temperatures

somewhere above freezing.

Once the spores germinate, mold begins to grow by forming an

extensive network of mycelium or hyphae that spread out across the

surface of the wood, and all the while producing more spores for

reproduction.

As we all know, mold will cause food stuffs to spoil. Mold is

also the cause of many plant diseases, such as the infamous Irish

potato famine of the mid 1800s. Moreover, mold can cause animal and

human diseases.

How does mold affect the health of people? Most people have no

reaction to mold, according to Dr. Eisenback. However, some people

have allergic reactions — similar to other allergies — that are

irritating but not life threatening. They may develop flu-like

symptoms and a skin rash. Mold can also make asthma more severe.

Fungal infection mold may become systemic in people with serious

immune disease. Also, some molds are known to produce mycotoxins

that can affect animal and human health and are known carcinogens.

People who are most affected by mold include the elderly, infants

and children, pregnant women, individuals with respiratory

conditions or allergies and asthma, and people with weakened immune

systems (for example, chemotherapy patients, organ or bone marrow

transplant recipients, and those with HIV infections or auto-immune

diseases). Clearly, mold can present a human health hazard.

Impact of Mold in Food Processing Environment

Dr. Rob at Virginia Tech's department of food science

and technology offers valuable insight from the food processing

industry perspective as to why moldy pallets cannot be tolerated.

Similar characteristics apply to the pharmaceutical industry.

First of all, the goals of any food processor are to produce safe

food, achieve the highest quality for the price, prevent product

loss, keep customers satisfied, and avoid regulatory enforcement.

From the perspective of the food industry, mold is a contaminant

that limits shelf life, threatens food safety and imposes

significant sanitation costs.

According to U.S. Economic Research Service estimates, 96 billion

lbs. of food are lost annually in the U.S. (27% of available food).

Among the key reasons for this loss is spoilage caused by mold.

Therefore, it is critical for food processors to extend shelf life,

ensure quality and prevent loss.

The four factors of shelf life include the formulation

(ingredients), processing, packaging, and storage conditions. Mold

can contaminate and inhibit the shelf life at every level of this

environment.

It is important to appreciate that federal regulations were

created to 1) protect public health, 2) protect the consumer from

fraud, and 3) to enforce the law. The Department of Agriculture and

the Food and Drug Administration are primarily responsible for

inspecting food processing facilities. Surprisingly, there are no

specific regulations regarding mold although highly dangerous

mycotoxins are regulated specifically. The regulations associated

with food inspections and mold pertain more to the fact that, due to

mold, food can be rendered unwholesome and unfit for human

consumption. For example, an inspector may determine that a given

product has become adulterated due to the presence of mold in the

food or in the storage environment (emphasis added). Given this

assessment, the inspector can immediately and temporarily shut down

production. Regulatory agencies may take action when " food has been

manufactured under such conditions that it is unfit for food " and

when " food has been prepared, packed, or held under unsanitary

conditions whereby it may have become contaminated with filth or

whereby it may have been rendered injurious to health " (emphasis

added). Similar regulations apply to the pharmaceutical industry.

In summary, mold is generally detrimental to food quality, and

sanitation depends on eliminating sources and reservoirs of spoilage

microorganisms. Processors wish to avoid violations of government

regulations to keep the inspectors away and avoid shut downs and

lost production. They cannot afford the risk that moldy pallets

impose.

How to Control Mold on Pallets

Effective mold control on wood pallets must begin with a

management commitment to a continuous, comprehensive mold control

program. The key components of a mold control program are: 1)

reducing airborne spore density around the manufacturing facility,

2) reducing wood surface moisture levels to below 20% moisture

content (average pallet part moisture content about 25%), and 3)

maintaining low wood surface moisture levels. Responsibility for

managing a mold control program should be centralized and assigned

to one person.

1. Reduce airborne mold spore density.

A regular inspection of all premises — building, grounds, raw

materials, and finished goods — should be performed at least twice

weekly. Mold can occur on any type of surface — wood, plastic,

metal, etc. Regular inspections will identify mold spore breeding

grounds and incidences of mold occurring on raw materials, finished

goods, or other possible sources of mold.

Spot treat to kill any existing mold with a 2:1 ratio of water to

household beach solution. The bleach kills existing mold and

prevents additional mold spores from being released, but it does not

prevent mold from reoccurring.

When possible, eliminate excess piles of wood debris and any

other unnecessary materials that can serve as breeding grounds for

mold spore. All storage areas should be well ventilated and well

drained (to eliminate standing water).

2. Dry pallets to an average moisture content below 25% before

shipping.

In general, dry pallets are superior to wet pallets in just about

every way. Dry pallets are stronger, more durable and weigh much

less than green pallets. They also prohibit germination of mold

spores and mold growth.

Although pallet manufacturers traditionally have not included a

pallet drying process in their operations, it would be

overwhelmingly beneficial.

Where mold is a concern, wood that has an average moisture

content of around 25% should have a surface moisture content of 20%

or less to prevent mold spore germination.

A fan drying system is an extremely effective and cost efficient

method to dramatically accelerate the rate of drying for wood

pallets. Inside a shed, pallets should be arranged in neat rows and

columns with space between to allow air flow across all wood

surfaces. This air flow allows moisture in the wood to wick away

from the surface and enables a steady rate of drying. The fans

should be reversed periodically to foster even drying throughout the

shed. Stringers should be aligned parallel to the direction of air

flow.

A fan shed will not only protect the pallets from the elements

(i.e. rain) but will more than double the rate of drying. It is

common for green hardwood pallets stored in fan sheds to reach 20%

moisture content in 10-21 days, depending on ambient air temperature

and relative humidity. This will significantly limit mold growth on

pallets.

Fan sheds in combination with chemical fungicide dip treatments

have proven very effective at preventing mold growth on pallets (as

long as they are kept dry during shipment, future storage, and use).

A chemical fungicide dip treatment for pallet parts will provide an

effective barrier to temporarily prevent mold growth and allow time

for drying. The chemical treatment itself does not provide permanent

mold protection; dry pallets ultimately prevent mold from growing.

Fungicide treatments are effective for around three weeks to a

couple months—depending on concentration levels and environmental

conditions. They can also be used in combination with wood

brighteners to achieve a bright and natural wood color.

The most efficient chemical treatment technique is to dip treat

dead-stacked parts (lightly banded to allow chemical penetration

into the stack). The parts only need to be submerged for a couple

minutes, then allowed to drip dry for one to two days before pallet

assembly. Spraying with fungicide may be necessary to maintain

vigilance against mold growth as pallets dry in the storage area.

Mold will not grow on pallets that are frozen during the winter.

However, if pallets are stored in heated buildings, they will

support mold growth; under these conditions, the dip treatment,

followed by a fan drying or kiln drying strategy, must be used all

year.

The moisture content of wood pallet parts should be monitored and

recorded regularly to determine the effectiveness of the moisture

control program and the suitability of mold-free pallets ready for

shipment. Electric resistance meters can monitor moisture levels

below wood fiber saturation point (25% to 30% moisture content).

Random samples of each production run should be measured twice

weekly. The samples should be randomly located within the drying

area. Stringers and deck boards should be measured according to the

instructions of the meter manufacturer (species, etc).

It is common for heat-treatment systems to exacerbate the

occurrence of mold on wood pallets if they not properly ventilated

at the end of each cycle. This is caused by a build-up of humidity

in the chamber; the humidity condenses and re-wets pallet surfaces

when cooled down. The warm, wet wood surfaces provide ideal

conditions for mold spores to germinate.

For pallets that are heat-treated, a fully vented blow down cycle

(at least 30 to 60 minutes) is recommended at the end of the heat-

treating cycle to dry the wood surfaces. After the cycle, pallets

should be moved immediately to a fan drying area. Heat treatment in

combination with additional kiln drying is an effective way to both

meet international phyto­sanitation requirements and provide

significant drying in one step.

3. Maintain low wood surface moisture levels.

Maintain a sufficient inventory of mold-free pallets that have

been dried to an average of 25% moisture content. The best option

for shipping mold-free pallets is ventilated trailer vans. These

kind of trailer vans prevent humidity from rising and condensation

from occurring inside; ventilated vans will prevent rain

contamination but will also allow pallets to continue to dry during

shipping. Alternatively, pallets should not be left in closed

trailers for more than 24 hours.

Upon delivery, pallets should be stored and protected from rain

in a well ventilated area with good drainage (to eliminate standing

water). If pallet surfaces become wet, it is an opportunity for mold

spores to germinate and grow. Remember: mold spores are always

present.

Ideally, these procedures should encompass the entire scope of

the manufacturing operations to reduce mold spore density and mold

growth as they relate to all pallets and lumber. However, if this is

not feasible, apply the procedures for pallets with mold limitations

only, and keep them segregated from other pallets during storage,

treatment, and shipment.

Finally, it is important to note that no wood pallet can be

guaranteed mold-free. By following the above requirements, wood

pallets can be manufactured and delivered free of mold to the extent

that it will not be visible or create potential problems for the

customer. Yet, it is impossible to declare that these or any pallets

are free of mold. As previously noted, mold spores are present

everywhere in the environment — even on pallets that have been

manufactured in accordance with a sound mold prevention strategy.

Chemical fungicide treatments do not last forever, and if the

pallets get wet again later, mold spores can germinate and grow. The

customer must take responsibility for keeping wood pallets stored in

a dry place.

Virginia Tech and the U.S. Forest Service Wood Education &

Resource Center recently launched a Web site dedicated to helping

pallet manufacturers stay informed about mold issues; the site is

located at www.palletmold.com.

The Web site currently includes all speaker presentations given

during the June mold conference and links to numerous drying and

chemical treatment companies. Additional information will be posted

as it becomes available.

For more information, contact Hamner at (540) 231-3043 or e-

mail phamner@....