Preservatives and shelf life: what keeps a ready meal safe

The word วัตถุกันเสีย, preservative, in a chilled meal's ingredients list tells you what went into the recipe. It does not tell you whether that meal stays safe longer than one without it. Shelf life comes from several controls working together, and a preservative is only one of them.

A preservative slows microbes down

Food spoils mainly because bacteria, yeasts and moulds grow in it, and some of those microbes cause food poisoning. Preservatives slow that growth: FSANZ's example is sulphur dioxide (220) in sausage meat, used to "limit microbial growth" (FSANZ). Antioxidants, a close relative, deal with a different problem, deterioration caused by oxidation, such as fats going rancid (EFSA).

Groups you may meet on labels, with their Australian code numbers (Better Health Channel):

EFSA's examples of use include nitrates and nitrites in meat, fish and cheese products (EFSA).

"Permitted" means assessed, limited and open to review

In the EU, no additive goes into food without a safety evaluation; authorities then set conditions of use, including labelling and maximum permitted levels, and EFSA is re-evaluating additives approved before 2009 (EFSA). In Australia the safe intake for people is set at about 100 times below the highest dose that showed no observable effect in testing, and approval can be withdrawn if new evidence shows an additive is no longer safe (Better Health Channel).

Thailand regulates food additives through Ministry of Public Health notifications (Thai FDA). On a Thai label, a preservative must appear under its functional class, วัตถุกันเสีย, with its name or INS number; unlike some other additives, it cannot hide behind the generic words "food additive" (Thai FDA, No. 450).

A small number of people do react to particular additives. Sulphites are the known example: Thai labelling rules list sulphites at 10 mg/kg or more among the substances that need an allergy statement. Those people have reason to read labels closely; everyone else has no reason to fear preservatives.

Shelf life is built from hurdles

Food safety specialists think in "hurdles" that together keep microbes in check, as a Codex draft code of practice for refrigerated packaged foods describes (FAO/Codex):

• Cold slows spoilage and the growth of most pathogens, but only if the food stays cold all the way from packing to eating.
• Heat treatment kills many microbes, yet on its own does not make chilled food sterile.
• A lower pH and lower water activity make life harder for bacteria, which is why pickles and jams keep longer than a creamy sauce.
• Hygiene in the kitchen and during packing means fewer microbes start the clock.
• A closed pack protects food from new contamination after cooking.

Each hurdle is partial. The maker sets the date on the pack with all of them in mind.

Is a meal without preservatives safer?

Not automatically. A meal with no added preservatives is safe when the other hurdles do their job and you eat it in time, and a meal with permitted preservatives is not unsafe because of them. Preferring one or the other is a fair personal choice.

Without that hurdle, the others carry more weight

We don't add preservatives when cooking and don't use ingredients that contain them. The choice concerns ingredients only: it does not make a meal keep longer or replace food safety control. Three things are left in your hands.

1. Respect the use-by date. It is about safety, and food should not be eaten after it (FSANZ). Every meal has a use-by date on the pack.
2. Keep it chilled. Meals in our machines are chilled, not frozen, and we monitor the temperature inside our machines remotely. Once the meal leaves the machine, the cold chain is yours: refrigerate it if you are not eating straight away, and keep it out of hot rooms and cars; Thai heat raises the stakes (the cold chain in a hot climate).
3. Heat it as the pack says. Packs carry reheating instructions written for that dish.

Frozen meals need different handling (chilled vs frozen meals). To find the วัตถุกันเสีย line on a pack, use our guide to reading a ready meal pack; MSG, the other additive people often ask about, has its own article.