Contact Time and Concentration: Using Sanitisers Correctly

Sanitisers only kill bacteria when used at the correct concentration for the correct contact time. Too dilute or wiped off too soon, and pathogens survive on food-contact surfaces. Mix to the label's ppm, apply after cleaning, and let the surface stay visibly wet for the stated dwell time — often 30 seconds to several minutes — before air-drying. Concentration and contact time work together; neither alone sanitises. Key takeaways: Concentration and contact time are equally essential — a correctly mixed sanitiser still fails if it is wiped off before its dwell time is up.. Sanitiser only works on a clean surface; food, grease and debris shield bacteria and can neutralise the chemical, so always clean first.. Mix to the label's stated concentration (usually measured in ppm) and verify it with matched test strips rather than guessing.. Keep the surface visibly wet for the full contact time on the label, then air-dry instead of wiping.. Approved chemicals and documentation rules vary by state and territory — confirm what applies with your local council or regulator.. Why concentration and contact time both matter Sanitising is a chemical process, and like any chemical process it needs both the right dose and enough time to complete. Concentration decides whether there is enough active chemical present to damage and kill bacterial cells on the surface. Contact time decides whether that chemical is given long enough to actually do it. If either one is wrong, the surface is not genuinely sanitised — it may only look and feel clean. The most common failure in a busy kitchen is spraying sanitiser on and wiping it straight off. The solution might have been mixed at exactly the right strength, but with only a second or two of contact it never reached the kill time printed on the label. The reverse fails too: leaving a solution that is too dilute sitting for several minutes will not make up for a shortage of active chemical. Concentration and time only work as a pair. Under Standard 3.2.2 of the Australia New Zealand Food Standards Code, food businesses must keep food-contact surfaces and equipment in a clean and sanitary condition. In day-to-day practice, meeting that duty means treating the label's stated concentration and its stated contact time as two halves of the same task, every single time you sanitise. Clean first, then sanitise A sanitiser is not a cleaner, and the two jobs are not interchangeable. Sanitiser is formulated to reduce microorganisms on a surface that is already visibly clean. Food residue, grease and protein get in the way in two ways: they physically shield bacteria from the chemical, and with several common sanitiser types they chemically react with and neutralise the active ingredient. Spray sanitiser onto a greasy bench and much of it is simply consumed by the soil. Effective practice is a two-stage routine. First, wash the surface with detergent and warm water to lift and remove visible food and grease, rinsing afterwards if the detergent directions require it. Second, apply the sanitiser to the now-clean surface at the correct concentration and leave it for the full contact time. Some products are marketed as combined cleaner-sanitisers, but a heavily soiled surface still needs a genuine cleaning step before the sanitising step can achieve anything. This clean-then-sanitise sequence is the baseline expectation for food-contact surfaces across Australian jurisdictions, even though the specific approved chemicals, concentrations and methods can differ — confirm the details that apply to your premises with your local council or regulator. Getting the concentration right Every registered food-contact sanitiser carries a concentration range on its label, usually expressed in parts per million (ppm) of the active ingredient. That range is the tested window in which the product is both effective against bacteria and safe to use on surfaces that touch food. Mix below the range and you leave bacteria alive; mix above it and you can leave harmful chemical residues, corrode equipment and waste product — without sanitising any faster than the correct dose. Never judge concentration by smell, colour or "a decent splash in the bucket". Measure both the sanitiser and the water, and then confirm the made-up solution with test strips or a test kit that matches your sanitiser. Chlorine-based and quaternary ammonium (QAC) sanitisers use different test strips, so choose the right one and read it against its colour chart rather than guessing. Concentration also falls during normal use. Soil load, dilution from wet wiping cloths, evaporation and simple elapsed time all weaken a working solution over a shift. Re-test periodically through the day, and make up a fresh batch instead of topping up a tired, cloudy one and hoping it is still at strength. Below the label range: bacteria survive and the surface is not sanitised.. Within the range: effective and safe on food-contact surfaces.. Above the range: residues, corrosion and wasted product — with no faster kill.. Getting the contact time right Contact time — often called dwell time — is the minimum period the sanitiser has to stay wet on the surface to kill the organisms it is rated against. Manufacturers establish it through testing and print it on the label, and it commonly ranges from around 30 seconds up to several minutes depending on the product and its active ingredient. The practical rule follows directly: the surface must stay visibly wet for the entire contact time. If the film of sanitiser dries early, or you wipe it away to keep moving, the reaction stops before it has finished and surviving bacteria remain. On warm or fast-drying surfaces you may need to reapply so the wet film genuinely lasts the full stated period. Once the contact time has been met, most food-contact sanitisers are designed to be left to air-dry. Air-drying both lets the product finish working and avoids recontaminating the surface with a used cloth, so it is usually better to walk away than to towel the bench dry — unless the label specifically directs a potable-water rinse. Water temperature, pH and other factors Sanitisers are sensitive to the water they are diluted with. Water temperature outside the label's range can slow the chemical action, and for chlorine-based products excessively hot water can drive off the active ingredient so the solution weakens much faster than expected. Very hard water and an incorrect pH can also cut the performance of some products. The fix is to follow the label's mixing and temperature guidance, use potable water, and store the concentrate as directed and out of direct heat and light. Keep test strips in date and dry inside their container, because degraded strips give false readings that can hide a weak solution and create false confidence. Because all of these variables interact, the most reliable habit is to make small batches often, verify each fresh batch with test strips, and discard any solution that has turned cloudy, heavily soiled or simply old rather than trusting it to still be within range. Recording, verifying and staying compliant Standards 3.2.2 and 3.2.2A frame cleaning and sanitising not only as things a food business must do, but increasingly as things it should be able to show it does. Many businesses record their sanitiser checks — concentration readings, and where relevant the areas and equipment covered — as part of a documented food safety program. Verification is as important as the task itself. A quick test-strip reading on each fresh solution, repeated through service, is far stronger evidence that surfaces were genuinely sanitised at the right strength than a tick or a signature on its own. It also catches weak batches before they are used on the line. Exactly what is required — including whether a documented food safety program or a qualified food safety supervisor is mandatory — varies by state and territory and by the type of food business you operate. Confirm what applies to your operation with your local council or regulator rather than assuming another venue's rules match yours. Checklist: Surface pre-cleaned and free of visible soil before sanitising. Sanitiser mixed to the label's stated concentration. Concentration confirmed with matched test strips. Water at the temperature specified on the label. Surface kept visibly wet for the full contact time. Correct rinse-or-air-dry step followed per the label. Fresh solution made up regularly rather than topped up. Test strips in date and stored dry. Common mistakes: Spraying sanitiser on and immediately wiping it off, cutting contact time to near zero. Diluting "by eye" so the solution is too weak to actually sanitise. Sanitising over food debris and grease that shield microbes and neutralise the chemical. Reusing the same cloudy, soiled solution all day as its strength drops. Assuming a stronger mix is always safer or works faster. Skipping test strips and never verifying the real concentration. Ignoring the label's water-temperature guidance.