Vol. IV · Knives, Tools and the Work Space Plate 7 of 10chopping board, hygiene, cross-contamination, washing, drying, wooden board, plastic boardST

Boards and Hygiene.

A board that is wet and dirty is a place for bacteria to grow. Clean and dry, it is not.

Cutting raw chicken leaves its juices, and whatever bacteria they carry, on the board and the knife. What happens next decides whether the next food cut on that board is safe. Left wet and dirty at room temperature, the board gives bacteria water, food and time (I.8). Washed in hot soapy water and rinsed, it loses most of them at once; dried, it starves the survivors, because most bacteria need water activity above about 0.9 (III.9).

The commonest mistake is not the board but the cloth: a damp cloth wiped over a board spreads bacteria thinly over everything it touches next, and a wet cloth left in a warm kitchen grows its own. The workshop follows the board through three choices. Its numbers are a teaching model built on the course's growth parameters, not measurements of particular boards.

Below: bacteria per square centimetre on a board after raw chicken (log scale), over the hours you choose, for a board left wet, wiped with a damp cloth, or washed and dried.

What you will learn
Workshop
Teaching model: Salmonella from 10 000 per cm² (log 4) at 22 °C. Left wet: grows with water activity 0.99. Wiped: one log fewer, still wet. Washed with hot soapy water: about three logs fewer, then dry (water activity below growth limits, slow die-off).

Wash, rinse, dry — and keep raw apart

In this model a board left dirty and wet for six hours in a 22 °C kitchen goes from 10⁴ to about 10^4.9 bacteria per square centimetre; wiped with a damp cloth it is only a step behind (10^3.9); washed in hot soapy water, rinsed and left to dry, it falls to about 10^0.4, a difference of 4.5 powers of ten. Drying matters as much as washing: bacteria that survive the wash cannot grow on a dry surface.

Wood or plastic? Both are safe if cleaned and dried; hardwood boards are kinder to knives, and studies have found that bacteria on clean, dry wood decline quickly. Plastic boards can go in a dishwasher, which helps, but deeply scored plastic is hard to clean and should be replaced. What matters more is separation: one board (and knife) for raw meat, poultry and fish, another for bread, fruit, salad and cooked food — colour-coded boards make this easy. Wash cloths hot and dry them, or use paper towels for raw-meat spills.

At the stove

Choose one board for raw meat only — mark it or buy a different colour — and keep it for that. After use, scrub it with hot soapy water, rinse it and stand it on its edge to dry. Put kitchen cloths in a hot wash every day or two.

The U.S. Food Code requires food-contact surfaces to be cleaned and sanitised between raw animal foods and ready-to-eat foods; in homes, hot soapy water followed by thorough drying does most of the same work.

Terms

Food-contact surface
Any surface that touches food: boards, knives, plates, counters.
Sanitising
Reducing microbes on a cleaned surface to safe levels with heat or a chemical sanitiser.
Cross-contact board
A board used for raw meat that must not then be used for ready-to-eat food without washing.
Colour-coding
Using boards of different colours for raw meat, fish, vegetables and cooked food.
Bacteria need water and time on a board: wash it hot, dry it, and keep raw meat on its own board.

Sources

  1. U.S. Food and Drug Administration, Food Code 2022 (sections 3-401.11, 3-403.11, 3-501.14, 3-501.16, 3-402.11 and the definition of time/temperature control for safety food).
  2. World Health Organization, Five Keys to Safer Food Manual, 2006.
  3. A teaching value chosen for the course: the right order of magnitude and shape, not a measurement of a particular food.