Aging Cheese on Wood Shelves and Food Safety – a Non-Issue

Wood Shelves
Don’t be afraid!

As a person who tends to want to follow rules, it is sad to be reminded that a good portion of food production regulations have little to do with actual food safety, rather they are the result of a ponderous, rigid system that steam rolls forward, sometimes based more on the ease of generalizing rather than the complexity of reality. The FDA has never liked wood shelves, especially when you sit food, in this case naturally rinded cheese, directly on its porous surface. Wood does not fit their Good Manufacturing Practice (GMP) model for a cleanable surface. While wood aging shelves have technically never been okay with the FDA, they have until now been mostly ignored and the decision to allow them been left to individual states .In many” big cheese” states, the regulators defer to the scientific knowledge of the leading expert within each state. For example, in both Oregon and Wisconsin (where at least 30 million pounds of cheese is aged on wood each year) the departments of agriculture have an official stance of “no wood shelves”. But in both states if a cheesemaker gets a thumbs up from the academic expert regarding their maintenance protocol for the shelves, then they have been allowed.

Isn’t that sensible? Did you hear me mention the words “scientific knowledge”? Let’s review what is well researched and known about wood shelves. (I’ll give you some references at the end of this post). Guess how many outbreaks of food borne illness they have been implicated in since the dawn of cheesemaking? Zero. This doesn’t mean that pathogens can’t exist on a wood shelf. If a cheese is contaminated and the wood poorly cared for, it will pass it to the shelf, no matter what material it is made from. Contamination of any aging shelf can happen when poor practices occur at any stage of cheese production, but it is not any more likely when wood is used. Bottom line.

Pros and Cons

So why do cheesemakers and affinuers (the folks that age cheese) love wood shelving? Tradition? Romance? Practicality? In the days before the invention of plastic, that ubiquitous, malleable material that we now take so for granted, wood was the logical and singular option. But fortunately it was also perfect. Like naturally aging cheese, wood “breathes”, it holds moisture without being wet, pulling it both out of the cheese, but also helping keep the aging space at a steady level of humidity. Not unlike the natural stone walls and bricks of the pre-modern aging space. Wood shelves used in aging room also take on the same family of fantastically helpful microflora – yeasts, molds, and especially bacteria – that help create distinctive, out-of-this-world cheeses. The usefulness of these microbes has not only to do with flavor, but also with the final safety of the cheese.

Given what I have just told you about how awesome wood shelving is, why isn’t everyone using it? (At least 60% of American Cheese Society cheesemaker members do) Or at least trying to use it? First it is, not surprisingly, highly discouraged thanks to the stance of our federal friends.  Second, the knowledge of how to properly care for wood is tucked away in the minds of a few and only a smattering of books and papers. Third many make only fresh cheeses where aging is not used. And finally, it is more work. More work is not what most cheesemakers need or can even contemplate. Let me tell you about our experience with wood shelves in our own aging room.

Wood Shelves at Pholia Farm

A few years ago we got permission from our inspectors to use wood shelves as long as we consulted with Dr. Lisbeth Goddik,Oregon State University’s Dairy Extension Specialist – a darned amazing woman. She suggested routine cleaning of the shelves with mild soap and warm water, then after rinsing with plain water either wiping the boards down with vinegar or a lactic acid bacteria wash. We did both. We marked which side of each shelf was treated with vinegar and which with bacteria. After aging the cheeses for many months, and before selling them, we swabbed the shelves and sent samples of the cheese to Agrimark lab. All results, for cheese and shelves, whether vinegar or lactic acid bacteria washed, were free from pathogens. So why did we stop? Ironically enough it was another aging room reality that is on the FDA’s hit list (not recent hits list…) cheese mites. I won’t go into too much detail about these little buggers (see one of my most popular posts for all of the itchy details), but what is pertinent is that the dark underside of the cheese sitting on the board was very desirable real estate for the mites. This required more frequent cheese rind labor, something that we were not prepared to do at that time. But I am now.

 So Why the Ruling?

Consider for a moment that the FDA is tasked with an enormous responsibility. As that responsibility grows and food systems expand it becomes more expeditious to simplify. This means generalized rules that apply to everyone – versus thoughtful, logical exceptions. Think about it, before a couple of decades ago, you would be hard pressed (like one of those fabulous wood aged European Comtes) to find any US made cheese that was aged in a cellar type situation with a natural rind. Consequently the paradigm for aging became a squeaky clean walk in cooler. The regulations that developed reflected that reality. With the looming burden of the Food Safety Modernization Act, it’s not surprising that they are now seeking to streamline and enforce existing regulations, rather than allow states to take the responsibility of allowing exceptions.

As we move forward as cheesemakers, I think we need to nurture a new paradigm, one in which the aging room is not treated as a processing room, but as a separate type of space in which a different set of GMP’s apply. When I was at a cheese science conference in England, it was repeatedly said that “The dairy/cheese plant is NOT A HOSPITAL”, nothing could be more true in a room in which you are counting on microbes to flourish.

What Can We Do?

I am a member of the American Cheese Society’s Regulatory and Academic committee. This morning (June 10th) we finalized the press release and position of the largest body of cheese professionals in the United States. (See the document at: 

Click to access ACS-Statement-on-Safety-of-Aging-Cheese-on-Wood.pdf


So support ACS (join if you are not a member), contact your state representatives, let the FDA know how you feel, and most importantly keep buying and making great cheese! Now, I am going to go put those beautiful Pacific maple shelves back in the aging room. Watch out cheese mites, I’m watching you!

The best overall summary of the topic: Donnelly, Catherine, Cheese and Microbes (2014), American Society for Microbiologists, 171-174
Ak, N. O., Cliver, D. O., & Kasparl, C. W. (1994). Decontamination of Plastic and Wooden Cutting Boards for Kitchen Use. Journal of Food Production, 57, 23–30.

Guillier, L., Stahl, V., Hezard, B., Notz, E., & Briandet, R. (2008). Modelling the competitive growth between Listeria monocytogenes and biofilm microflora of smear cheese wooden shelves. International Journal of Food Microbiology, 128, 51–57.

Mariani, C., Briandet, R., Chamba, J.-F., Notz, E., Carnet-Pantiez, A., Eyoug, R. N., & Oulahal, N. (2007). Biofilm ecology of wooden shelves used in ripening the French raw milk smear cheese Reblochon de Savoie. Journal of Dairy Science, 90, 1653–1661. 

Mariani, C., Oulahal, N., Chamba, J.-F., Dubois-Brissonnet, F., Notz, E., & Briandet, R. (2011). Inhibition of Listeria monocytogenes by resident biofilms present on wooden shelves used for cheese ripening. Food Control. 

Nese, AK, Cliver, Dean, Kaspar, C. (1994). Cutting Boards of Plastic and Wood Contaminated Experimentally with Bacteria. Journal of Food Protection, 57(1), 16–22.

Oulahal, N., Adt, I., Mariani, C., Carnet-Pantiez, A., Notz, E., & Degraeve, P. (2009). Examination of wooden shelves used in the ripening of a raw milk smear cheese by FTIR spectroscopy. Food Control. 

Schvartzman, M. S., Maffre, A., Tenenhaus-Aziza, F., Sanaa, M., Butler, F., & Jordan, K. (2011). Modelling the fate of Listeria monocytogenes during manufacture and ripening of smeared cheese made with pasteurised or raw milk. International Journal of Food Microbiology, 145 Suppl 1, S31–S38. 

Zangerl, P., Matlschweiger, C., Dillinger, K., & Eliskases-Lechner, F. (2010). Survival of Listeria monocytogenes after cleaning and sanitation of wooden shelves used for cheese ripening. European Journal of Wood and Wood Products, 68(4), 415–419. 


Cheese Mites- A Creepy Little Secret

Here is an article I wrote awhile back on the fun little problem that comes with aging naturally rinded cheeses:

How the “Mitey” Have Fallen- Adventures with Cheese Mites

By Gianaclis Caldwell

May 2010

Cheese lovers beware, there is another very determined turophile (cheese devotee) on a mission to devour the same fine, long aged cheeses that you too love to eat. These little pests can consume a significant portion of aged, naturally rinded cheeses and in the process take a bite out of the slim profit margin of the artisan cheesemaker.  While cheese mites are a desired part of the aging of a handful of European cheeses, for most cheesemakers they can be a costly nuisance.

I remember when cheese mites first arrived in our aging room.  For many months I innocently thought the brownish powder accumulating on the aging room floor between cleanings, of course, was “cheese dust”- some sort of naturally occurring shedding of the paprika and oil rubbed rinds of our cheeses.  This naiveté served me well until I visited a fellow cheesemaker who was brushing the same dust off of her cheeses and complaining about mites.  Did I have cheese mites? She asked.  No, I didn’t think so, I replied while at the same time the realization started dawning that I did indeed have my own little infestation going on back home in the cellar.  Upon returning to our farm and creamery I put a bit of said dust on a microscope slide, placed it under the lens, took a look and was disgusted to see the little creeps waving back at me.

It seems that there are mites for every occasion and morsel- cheese mites, flour mites, mold mites, dust mites, and so on, and many of them are not too picky to also eat out of their specialty. It is through this versatility that mites find their way to the aging cellar. Since most of us do a little baking or know someone who does, we become the unknowing host to some little hitchhikers.  Mites are known to attach themselves to hair, clothing, and even flies in their quest for the good life.   I talked to one cheesemonger who said she and her staff would hold “cheese mite races” if they were bored.  Now, remember these are not speedy creatures, so I am not sure exactly how much excitement a mite race could generate, but it does sound creative and somewhat job related…

Let’s talk about that “cheese dust” a bit more.  What the heck is it?  Well, for those of you who have seen electron microscope images of dust mites that live in all of our beds (yes, everyone’s) and the little creatures that live at the base of our eyelashes, you can picture what this cheese dust looks like up close- eight legged mites, living and dead, and their excrement (it’s true, “Everyone Poops”).   The good news is that cheese/mite dust doesn’t pose a health risk to us full sized cheese lovers and makers.  There are cases where dermatitis (itchy skin) is a problem for some people exposed to cheese, flour, and mold mites, but usually there are no ill effects (unless you have a weak stomach and make the mistake of looking at them under a microscope right before dinner…)

So what does the cheese mite do to its prey? They dig in and start eating the rind of unwaxed and otherwise unprotected aging cheeses, including bandage wrapped cheddars.  Generally they don’t start to work on cheese under a couple of months of age, (they seem to have a connoisseur’s taste, but actually the longer aged cheese has a greater degree of protein breakdown- proteolysis- making it a better source of nutrition for the mite),  but it varies depending upon the rind treatment.  For example, cheeses that are being brine washed or rubbed with oil usually don’t see any mite presence until much later in their aging or, if rind treatment continues throughout aging, their activity is limited (the small size of the mite makes it difficult for them to maneuver through sticky, oily, or wet surfaces).  As the mites dine, they create little pinholes (see photo) that later turn into growing craters.  They eat their way under the rind and eventually cause large pits, and what I think of as cheese sink holes.  Initially the damage they do has no effect upon the taste of the cheese, but given time they impart a floral, sweet, rather sickly (to my taste buds) flavor.

So why would anyone want mites on their cheese?  Two fairly well known European cheeses, the German MIlbenkäse (literally mite cheese) and the French Mimolette are probably the two best known examples of cheeses using, what I like to call, mite-assisted-affinage. MIlbenkäse manufacture utilizes mites in an interesting fashion; when the wheels, logs, or other shaped cheeses are ready, they are placed in a box (mites prefer the dark) with mite dust and rye flour.  Evidently the flour provides an additional food source for the mites so that they will still have an effect on the flavor of the cheese, but consume less of the finished product.  Mimolette wheels (whose shape and make is similar to Dutch Edam) are also inoculated with mite dust and then brushed throughout the rest of their aging, to somewhat slow the destruction of the rind while the flavor can be changed by the mite’s activity.

If you are an artisan cheesemaker with a mite “problem” it can be utilized to produce a unique product, but it is important to remember that most retailers will not appreciate a heavily infested cheese being introduced to their cheese case or aging rooms.  In addition, health departments may not recognize mites as an acceptable “ingredient” in cheese.  So what can you do?  There are several options for limiting the damage and level of involvement of these little guys in your aging room.

One of the key factors in limiting mite damage is early intervention.  Once the mites work their way under the surface of the cheese they gain a measure of protection from any attempts to disrupt them. If your cheese isn’t intended to age for more than a few months, this may not be an issue.  Mechanical means of limiting mites included brushing and vacuuming (yup, now your housework extends to the aging cellar).  If brushing, it is best to remove the cheeses from the aging room and brush then onto a damp floor or into a sink, so that the dust is better contained.  Vacuuming can be done with a small vacuum that you keep just for this purpose.  Remember, the running motor will generate heat, which could be a factor for your cooling system.  Both vacuuming and brushing will need to be done very regularly to have much effect, and again, remember that if the mites have already gone “underground” on your rind, these methods will do little good.

Mites also seem to prefer a flat surface and dark, so you will see more activity on the underneath side of a wheel that is aged on its flat surfaces.  Wheels that are aged on their curved sides seem to suffer a bit less damage, as do those not aged on wood.  (It isn’t the wood that is the problem, it is just that the wood helps keep the mites dark and protected- they can’t fall off the wheel as easily!)  When we had some large losses due to mites, we were aging on wood.  Until that time the damage was always minimal.  I tried vacuuming while aging on the wood, but it was difficult to effectively get all of the mite dust off of the wood without moving every cheese on the shelves, and, as I mentioned before, the vacuum generated quite a bit of heat in our small aging room.  We are powered solely by solar power and any additional energy loads can be a concern.

Some data say that mites will not live at refrigeration temperature, so I tried chilling cheeses for a period of days before shipping.  About all that did was slow the mites down.  Some research says that mites can be controlled with temperatures less than 37.4 F (3 C), but that wasn’t my experience with cheese already infested.  And of course, most artisan cheeses would not be aged at refrigeration temperatures, other than perhaps blue cheese.

Waxing, clear coating (sometimes called cream wax but really a polymer based coating), and vacuum sealing will of course prevent infestation, but bandaging will not.  In fact, it is bandage wrapped cheddars that seem to have the biggest problem.  In the past, aging rooms were fumigated to kill mites, but this, thankfully for the environment, is no longer acceptable or allowed.

Some cheesemakers have noted that mites seem to be more attracted to moldy cheeses.  Evidently molds produce pheromones that attract the mites.  The mites serve the mold’s purpose by helping move spores deeper into the cheese as they burrow their way into the rind.  They also open the rind up for natural spore invasion.  So steps that reduce mold growth , such as brushing and brine washing, will also help deter mite activity.

Many cheesemakers find the best remedy to be the use of food grade diatomaceous earth (DE).  When dusted (use a fine meshed sieve) on the surface of the cheese the DE dehydrates the mites. Again, this technique must be employed early in the aging process before the mites have gone below the rind’s surface.  Be sure to wear a mask when using DE, while not toxic, breathing the fine, abrasive powder is not a good thing for your lungs.

Hydrogen peroxide can be utilized when mixed to 10% as a wash either following vacuuming or before infestation occurs.  I have not tried this method, but somehow it sounds effective yet unappetizing if your rinds are typically consumed by customers.

Ozone machines are being used to limit mite damage in larger aging facilities- and some small ones.  What is an ozone machine?  Well, in a nutshell these machines take oxygen (O₂) from the room, utilize an ultra violet light, and change it to tri-atomic oxygen (O₃). Ozone attacks organic compounds, such as mold, yeast, phage, and bacteria.  It has been used for some time in hospitals and other institutions to purify air and has been shown to sanitize surfaces as well.  So how can this help with a cheese mite problem?  The research is unclear on the exact mechanics, but it seems that the mites don’t appreciate the O₃ environment and as mold growth is also limited by ozone, the cheese surface becomes less appealing.  At Pholia Farm we have a small ozone machine (the EQ Ecobox- about 349.00 on that we utilize for mildew prevention, air freshening, and general sanitation in the cheese make room, but I would never consider using it in our aging room where I want mold growth and bacterial activity.

So to sum it up, anything you can do to make the surface of your cheese less hospitable for mites will help; brine washing, oiling, brushing to limit mold growth, dusting with diatomaceous earth, vacuuming, and turning frequently.  If all else fails, perhaps there is room in theUSmarket for an new American original, perhaps a cheese called, say“Mitolette”?

“The Use of Ozone as a Disinfectant in Dairy Industry”, Technical bulletin No. 27, January 2003.  May 5, 2010

“Cheese Mites: They’re Back”, Melnyk, Boinder, Marcone, Scott-Dupree, and Hill, Department of Food Science and Environmental Biology, University of Guelph.   May 1, 2010 (Note, this article is no longer available at the link by which I accessed it)

Identification of Cheese Mite Species Innoculated on MImolette and…

“The Art of Farmstead Cheesemaking in the British Isles”, McKnight, Qui’tas,

The Babcock Institute for International Dairy Research and Development, Universityof Wisconsin-Madison,   May 3, 2010