30 years ago, researchers in Madison, Wisconsin, made a surprising discovery about wooden cutting boards, their safety, and compared them to plastic cutting boards. Here's what they found out and what scientists are still finding out today.

Preface: While the information below indicates certain boards are very low risk - it is important to note a single viable pathogen can cause an illness! Even if 50 units of bacteria are present on a cutting board - it is still possible, albeit low risk. Always wash (with soap & hot water) and dry ALL cutting boards to reduce your risk of foodborne illness.

UW-Madison Food Research Institute 1994 Study

In 1994, the University of Wisconsin (UW)-Madison Food Research Institute and related departments conducted a study where they deliberately contaminated wood and plastic cutting boards with bacteria such as E. Coli, Salmonella, and Listeria, and then tried to recover the bacteria immediately, as well as a few hours later.

The process:

The researchers loaded between 21 million and 27 million (depending on which trial) Colony Forming Units (CFU's) on a 2" square section of cutting board. These CFUs were often a single viable bacterial cell, but a CFU could also be hundreds of bacteria clustered and clumped together. Once loaded, they tried to recover them at the following time stamps:

1. Immediately (0 minutes) after contamination.

2. 3 or 10 minutes after contamination, depending on the trial.

3. 12–18 hours later, generally after overnight storage.

The researchers kept the overnight samples in a high-humidity chamber to prevent drying from influencing bacterial survival.

The researchers also used a combination of wood types, new cutting boards, and heavily knife-scarred surfaces.

Results:

Wood Vs. Plastic

Okay, but what about by wood type?

With the wood cutting boards contaminated, liquid was drawn into the wood within 3-10 minutes. Only 0.1-2% of the bacteria were recoverable on the surface 12 hours later, with millions of organisms sucked into the wood where, once trapped, they died. 

The study found that treating the board with mineral oil didn't substantially change the results, but oil treatments did prevent the wood from cracking. The issue with cracking is that it creates another surface for bacteria to cling to and, if not cleaned, it still provides a higher possibility for contamination.

With plastic cutting boards, the number of bacteria significantly increased on the surface of the cutting board over a 12-hour period, not decreased.

What about New Vs. Heavily Knife-Scarred boards?

With wood, the study found that whether new or heavily knife-scarred, bacteria became unrecoverable from the surface in much the same way. Wood generally cleaned effectively whether new or scarred, and even with chicken fat present, it was not nearly as bad as heavily scarred plastic.

With new plastic, the surface was relatively easy to clean and disinfect, but with scarred boards it became difficult to remove bacteria through ordinary handwashing. Deeply scarred plastic provided safe havens for bacteria to remain and multiply, even after cleaning.

Okay, but once they got sucked into the wood, what happened?

While the study didn't go further, by cutting into the wood and trying to recover the bacteria and see if they were alive/dead, what we know is that hardwood has two distinct things that lead us to indicate that the bacteria die. The first is that hardwood has naturally occurring polyphenols (such as tannins and stilbenes) that destroy the organisms. The second is that the porous nature of wood allows it to regulate the moisture content necessary for bacterial reproduction and survival. 

Why did glued cutting boards have a higher recoverable amount?

This is an excellent question, but it unfortunately is not something this particular study solved. What common sense tells us is that glue joints provide small surface areas, which are not porous in the same way wood is, and provide a slightly higher risk of bacteria being present on the surface. While we do not discourage people from buying laminated boards, and even occasionally make them ourselves, we encourage people to use solid wood when possible out of caution.

Summary:

In summary, we conclude the following:

• Plastic cutting boards are SAFE to use when new and thoroughly washed, but if heavily knife-scarred, they present a possible danger.
• Wood Cutting Boards - of all types, but especially hardwoods - are SAFE to use, but should still be thoroughly cleaned to eliminate even the slightest risk of foodborne illness.
• ALL cutting boards should be thoroughly washed to prevent the risk of foodborne illnesses.
  
• Oiling wooden cutting boards prevents cracking, which reduces the surfaces that bacteria have to hide in.
  
  

Links to study & credit:

Study Credit goes to 1994 University of Wisconsin-Madison by AK, Cliver, and Kaspar, published in the Journal of Food Protection, Volume 57, Issue 1, January 1994

https://bit.ly/47uLAjL