By Brad Gething, NWPCA Technical and PDS Manager
An increasing demand for mold-free wood packaging in the food and pharmaceutical sectors has led to a greater need to understand the finer points of the mold issue. In response to this need, NWPCA brought together two members of the wood packaging industry and one member of the wood preservation industry to discuss what can be done to combat mold, and how the industry can better educate customers to ensure that the wood packaging remains mold-free throughout its lifecycle. The discussion panel occurred at the Annual Leadership Convention at Ft. Lauderdale in March, 2014 and was moderated by NWPCA Technical and PDS™ manager Brad Gething.
The panel consisted of:
John Dye, Product Development Manager, Scott Pallets
Michael Pompeo, PhD, Director for Technical Development of the Osmose Inc.
Ralph Rupert, Manager Unit Load Technology, Millwood Incorporated
Wood packaging manufacturers need to recognize that wood material is potentially susceptible to mold growth the moment the tree is felled, and that susceptibility may increase as the tree is cut into cants and cut stock. A firm understanding of what mold is and what causes it will provide manufacturers with the foundation necessary to prevent mold growth. Mr. Rupert gave a strong presentation on this topic. He explained: “Mold spores are present everywhere in the environment and require several things to grow: oxygen, a food source and moisture. Realistically, moisture reduction is one of the only available methods to prevent mold growth. Overall, reduction to 19 percent moisture content (MC) has been shown to significantly reduce the likelihood of mold growth.”
The amount of moisture in wood can vary greatly depending on the tree species and how green the material is, and drying wood, particularly stacked as pallets, is inherently a variable process. John Dye explained that research performed in conjunction with Edinburgh Napier University showed that a target moisture content must be reported as a range, and not an exact number “because it cannot be precisely predicted or guaranteed.” This range does not mean that a reduction in moisture cannot provide increased confidence in mold prevention, but it does require improved communication between you and your customer to set the proper expectations. Consequently, Dye added, “TIMCON is focusing on efforts to educate end-users about environmental conditions that promote mold growth, instruct them on proper pallet storage and handling, and provide best practice guidance on kiln drying pallets manufactured from green timber.”
Mr. Rupert also described some popular misconceptions that exist about mold. “The most widely held misconception is that heat treatment prevents mold growth. While heat treatment may kill existing mold spores on the surface of the wood, its intended purpose is to kill insects and does not prevent future spores from growing, so post heat-treated material is not immune. In fact, the heat-treatment process tends to pull out internal moisture to the surface of the wood, which could actually lead to more attractive conditions for mold growth.” Secondly, in spite of the evidence that drying below 19 percent MC greatly limits mold growth, it does not guarantee that mold will not grow. In the right conditions, some of the remaining moisture in the wood will eventually come to the surface, and if it can accumulate sufficiently, mold can grow.
When moisture reduction is not suitable for your business, or the customer desires greater assurance against mold growth, chemical treatments can be an option. Dr. Pompeo outlined the major types of chemical treatments and how they are applied to wood packaging. He said, “There are several major moldicide suppliers in the U.S. which produce a variety of formulations. These formulations tend to be a mixture of several active ingredients and they are all EPA registered pesticides. A few substances are approved or exempted by the FDA as safe to use for food contact application, and they are known as Copper-8 and potassium sorbate. Potassium sorbate is in fact a food additive that functions as a preservative/moldicide. All of these products can either be applied through dipping or spraying processes.”
Dr. Pompeo was asked about the efficacy of different chemical treatments and was quick to point out that “effectiveness varies based on the type of formulation and environmental conditions. It is best to discuss these variables with a preservation expert and conduct field trials on specific applications to determine a probable timeframe that the wood will be protected from mold. Effective protection time, based on these variables, can range from as little as a few weeks to a few months or longer.” In general, if mold is already present on received cut stock and cants, or mold is found on existing wood packaging, the panelists recommended that a simple solution of water with bleach (10 to 1 ratio) or 3 percent concentration of hydrogen peroxide can be used to scrub or pressure wash the wood clean. Proper drying is needed to ensure that the mold does not return.
All three panelists emphasized that storage conditions are a critical aspect to mold prevention. In moist environments with little to no air flow, mold will grow on most anything, not only wood. Rupert said, “Trailers should be unloaded as soon as possible. They shouldn’t be called trailers, but incubators, since mold grows so easily inside them. Wood should be stored in ventilated areas to promote drying and inhibit mold growth. In fact, air velocity as low as a few feet per second can deter mold growth.”
Also, Mr. Dye pointed out that “keeping wood packaging elevated off the floor or ground to prevent any uptake of moisture is a simple and effective way of keeping the wood dry. This includes when pallets are placed in a kiln to dry.” Dr. Pompeo warned against outside exposure: “Outside storage in the rain or in warm/humid conditions is the worst case scenario for storage of wood articles.” If outdoor storage is the only option, covering should be provided to prevent such exposure to the rain, but should also provide enough air circulation as pointed out by Mr. Rupert.
From this discussion an overriding theme resulted: while the increasing desire for mold-free wood packaging is an ever-present matter for the industry, there are methods available to effectively control mold growth. The battle against mold must be fought on two fronts. First, diligence within each step of the supply chain is necessary to ensure that wood does not grow mold. Second, it is imperative for the wood packaging manufacturer to communicate clearly to the customer what environmental conditions are favorable for mold growth and what actions he or she must take to ensure prevention. Such a comprehensive approach can be a challenge, but it will provide an opportunity for companies to differentiate themselves in this competitive industry.
Brad Gething, PhD, is NWPCA's technical and PDS manager. He can be reached at 703-519-6104. Follow him on Twitter.