Kitchen cutting boards
The kitchen is a domestic microbe’s playground (well ahead of the bathroom for example). The kitchen sink, dishwashing sponges, linen towels and cutting surfaces can be teeming with microbes. In the US, about 200,000 cases of food-borne illnesses occur every day. Most of these illnesses have a domestic origin rather than a commercial (restaurant/canteen/fast food) one. In the home, cross-contamination from one food-group to another (e.g. from raw chicken to salad ingredients) is a prime mechanism and is often mediated by the cutting board.
So, is there a difference in the food-safety of cutting boards? Wood or plastic (synthetic)? It is a variant on the natural vs. artificial question. However, on balance, wood looks like it has the advantage this time around.
The advantage of a wooden cutting board is that wood is naturally antimicrobial.
Trees, like other plants, rely on chemical defences to maintain their health against a constant bombardment of opportunistic attack by microbes (bacteria, fungi, yeasts, viruses and some parasites). So, their wood contains a range of anti-bacterial and anti-fungal agents. These chemicals (mostly polyphenols, e.g. tannins) are not ‘living things’ and remain viable after the wood is harvested, providing a wooden cutting board with its antimicrobial properties.
Even the physical structure of wood is antimicrobial. The job of a tree trunk is to carry water from its roots to its leaves. Thus, wood fibres evolved to have a strong capillary action. Microbes are water-based lifeforms. When a microbe finds itself on a wooden board, the natural capillary action of the wood fibres suck water from the microbe and dehydrate it, thus killing it by desiccation. This is important for microbes that diffuse into the porous wood — they may not be removed by surface cleaning, but they die because of the chemical and structural properties of wood.
Knife cuts in cutting boards provide a breeding opportunity for microbes. In wood, these cuts can partially close up because wood swells when wet and because the fibres can re-bond. Chopping blocks (where the wood fibres run vertical to the surface rather than horizontal as in most wooden boards) have the added advantage that knife cuts don’t cut the wood fibres but rather push them apart — they go back to their normal position once the knife is removed.
However, plastic and synthetic boards have the advantage that they can be sanitised in a dishwasher set to a sufficient temperature. In general though, as plastic boards become steadily degraded by knife cuts their sanitisation becomes increasingly difficult. Plastic boards are non-porous and therefore microbes cannot be absorbed, however this advantage is undone by cuts. Wooden boards retain their safety with use. Some modern plastic boards are infused with antimicrobial agents (although the effectiveness is usually just assumed) and are often colour-coded as a reminder to reduce cross contamination. The convention is: raw fish; raw meat; salad and fruit; cooked meat; vegetables; dairy (white), although this necessitates the coordinated use of up to 6 cutting boards (which themselves could get cross-contaminated).
Some ‘synthetic’ cutting boards are manufactured from natural wood fibre composites and retain wood’s antimicrobial properties but are also dishwasher safe.
Not all woods are the same. Hardwoods with tight grains and small pores are usually recommended, however it seems that pine has one of the strongest antimicrobial properties. Bamboo is also thought to be antimicrobial and is a very dense wood with hygroscopic (desiccating) properties. Most wooden boards consist of smaller pieces glued together, so the food-safety of the glue is perhaps another consideration.
