Food plant sanitation
Use the ‘Stout Method’ to determine if allergen-containing dust poses a risk that could lead to a recall.

KANSAS CITY — In the processing and packaging areas of baking and snack facilities, allergen-containing dust has been identified as a potential cross-contamination point. It’s also a common observation that’s made during many audits, including those by Global Food Safety Initiative inspectors and others.

Specifically, the concern is that the contamination of non-allergenic foods by airborne dust and aerosols could contaminate products on an adjacent line due to general air movement, static electricity or by the use of compressed air to clean equipment.

To determine if this is a risk in your bakery or snack facility, you need to use a hazard analysis tool to verify whether the potential for dust cross-contamination exists and requires preventive control as defined by the Food Safety Modernization Act (FSMA).

This concern dates back to the January 2013 proposed FSMA rule: “Proposed §117.135(d)(2)(i) would require that food allergen controls include those procedures, processes and practices employed for ensuring protection of food from cross-contact, including during storage and use. Examples of such controls include procedures for separating ingredients and finished products that contain allergens from those that do not contain allergens, and procedures for separating foods that contain different allergens. Such controls are essential to prevent the inadvertent incorporation of an allergen into a product for which it is not an ingredient.”

Examples of such procedures for controlling food allergens include procedures that provide physical barriers; eliminate or minimize the formation of dust, aerosols or splashes; conduct manufacturing and processing of foods in different parts of a facility; emphasize separation in time, such as by production sequencing or by cleaning equipment between production runs; emphasize storage and handling appropriate to reduce the potential for cross-contact; and control the movement of tools and personnel that might carry allergens when the same production lines are used for both foods that contain allergens and foods that do not, or when the same production lines are used for foods that contain different allergens.

The Food Allergy Research and Resource Program (FARRP) has viewed dust cross-contamination in plants as a low risk. As a result, a baker’s primary focus should be on high-risk areas that include scheduling of product runs, controls during manufacturing (separate tools, GMPs, sequencing), effective cleaning between production runs, rework controls, and storage of allergen-­containing ingredients.

Given the level of interest in potential dust cross-contamination based on FSMA — and with dust being cited as a risk in audits — collaboration was initiated with multiple companies, FARRP and myself to conduct trials of a method to measure dust contamination from adjacent lines. Time spent on this project was pro bono by FARRP, which tested the many samples, and me. The goal of this exercise was to provide a science-based hazard analysis to evaluate risk. Up to this point, personal opinions on dust drove control decisions and audit comments. The resulting method allows collection and analytical analysis to make science-based decisions. Known by FARRP as the “Stout Method,” it has been presented to and applauded by the FARRP board.

The approach used in the test method is to ­scientifically measure the allergen dust generated by a processing, transfer, packaging or cleaning process. It also analyzes the impact to an adjacent open process, exposed contact surface or tools, which if exposed, could allow allergens to be incorporated into a product not formulated with that allergen.

Companies that volunteered to participate in these studies were concerned with potential allergen dust cross-contamination from adjacent line operations (processing, transfer packaging or cleaning). One study focused on cross-contamination by adjacent lines at multiple exposure points from process to packaging. Another targeted batch processes with intermittent exposure and concerns with adjacent line cleaning.

In the first model, multiple points where product was exposed were measured. This is referred to as the “continuous processing” scenario.

The second scenario involved a single point of exposure in a mixing vessel with a hatch cover, which was open for a set time when dust could enter the open mixer. Referred to as a “batch scale” scenario, this method is an excellent tool for measuring impact of adjacent line cleaning but only if air pressure is not used in the cleaning process. Using compressed air for cleaning an allergen line when an adjacent line is operating can propel heavy dust and particulates onto adjacent lines.

The Stout Method is based on the placement of multiple petri dishes next to the potential “allergen receiving line” to measure dust over multiple time periods while also measuring the exposure area, depth, weight and speed of the product. The residue in the petri dish is analyzed for allergen residue by FARRP. All of this information is inserted into a formula developed by FARRP and provides a mathematical calculation of potential ­allergen cross-contamination.

In summary, this method yields a complete hazard analysis of the potential for allergen dust cross-­contamination as recommended by FSMA rules. Once this information is created, it can provide insight about the risk of dust cross-contamination and whether a preventive control is needed. And if such a control is ­indeed needed, then the processing plant may have to provide separation between adjacent lines to control dust movement from one area to another.

Go to to find out more about this procedure.