Feeding & Nutrition

Fat begins to oxidise within hours of a bag being opened. Not weeks. Hours. The moment air hits the surface of that kibble, a slow chemical reaction starts pulling apart the fats that were sprayed on the outside to make the food palatable, and the same reaction quietly degrades vitamin A, vitamin E and thiamine along the way. A large bag of dog food fed to a small dog can sit open for two months. By week six, the food in the bottom of that bag is not the food you bought.

This is the least glamorous topic in pet nutrition and probably the one with the widest gap between what owners do and what they should do. People will spend forty pounds on a premium food and then store it in a way that undoes half of what they paid for.

The core problem is rancidity, and it comes in two flavours. Oxidative rancidity is the common one — oxygen attacking unsaturated fats, producing peroxides and eventually the aldehydes that give old food that faintly waxy, crayon-like, cardboard smell. Hydrolytic rancidity involves water and produces a sharper, soapy note. Heat, light, oxygen and moisture all accelerate both. Fish-based foods and those rich in omega-3s go off fastest, because polyunsaturated fats are the most vulnerable to oxidation, which is a genuinely irritating irony given that omega-3s are one of the main reasons people buy those foods.

A rancid food is not usually going to poison a healthy adult dog. What it will do is taste bad, smell wrong, and deliver less of the vitamin content printed on the label. Some pets get loose stools from it. Fussy eaters simply stop eating, and their owner concludes the pet has gone off the brand when really the pet has gone off that particular bag. In more serious historical cases, oxidised fats have been linked to thiamine deficiency, and thiamine deficiency in cats causes neurological signs that are frightening to watch.

Keep the bag, and stop pouring kibble into the bin

Here is the single change most households need to make. That plastic storage container everyone buys is fine as an outer vessel and terrible as a direct food contact surface. Kibble fat seeps into the plastic, builds a film on the walls, and that film goes rancid. You then pour fresh food on top of a rancid coating and re-contaminate every new bag. If you have been using the same bin for two years without a proper wash, run your finger round the inside. It will come out greasy, and it will smell.

The better method is to put the entire original bag, folded down and clipped, inside the container. Modern pet food bags are multi-layer, often with a foil or metallised barrier layer specifically engineered to block oxygen and light. They are far better at their job than a translucent plastic tub. Keeping the bag also keeps the batch code, best-before date and lot number, which is exactly the information you need if there is ever a recall or if your pet reacts badly and you have to report it. Tip the food out and that information goes in the recycling.

Wash the container itself with hot soapy water and dry it completely between bags — completely, because residual moisture in a food bin is how you get mould. If you must decant, use stainless steel or food-grade glass, and buy smaller bags more often rather than the giant economy sack.

Buy a bag size your pet will finish in about four to six weeks. A 6 kg cat eating 55 g of dry food a day gets through 1.65 kg a month, so a 2 kg bag is right and a 7 kg bag is false economy. Store it somewhere cool and dark, ideally under 26 degrees Celsius, which rules out the garage in summer, the shed, the cupboard above the oven and the spot beside the boiler. A pantry or a low kitchen cupboard on an outside wall is usually the coolest place in a house.

Wet food, freezing, and the bowl nobody washes

An opened tin or pouch of wet food keeps five to seven days in the fridge, covered, and I would treat five as the real limit for a cat with a sensitive stomach. Do not leave the metal tin uncovered in the fridge — transfer it to a lidded glass container or use a proper tin cap, because exposed food picks up fridge odours and dries at the surface. Wet food left out at room temperature should be picked up after 20 to 30 minutes in a warm kitchen, four hours absolute maximum in a cool one. Bacterial growth on moist meat at room temperature is fast, and in warm weather it is very fast.

Freezing works well for wet food and raw diets. Portion into ice cube trays or small tubs, freeze for up to three months, and thaw in the fridge overnight rather than on the counter. Dry food freezes too if you have been given a huge bag — split it into sealed portions and let each one come to room temperature still sealed, so condensation forms on the outside rather than on the food.

Then there are the bowls, which are the part of pet food storage everyone forgets. Food bowls should be washed daily with hot water and detergent, and water bowls too. A study of household surfaces by the American public health body NSF put pet bowls in the top five germiest items in the average home, alongside sponges and dishcloths. Biofilm builds on plastic within days and it is exactly the slimy layer that harbours bacteria. Stainless steel in the dishwasher solves this in one move. Scoops need washing as well; the one that lives buried in the kibble picks up fat and dust and never sees soap.

Learn what fresh smells like. Open a new bag and take a proper sniff — that toasty, faintly fatty smell is your baseline. When a bag smells sour, chemical or like old crayons, or the kibble looks dusty and pale where it was glossy, throw it out. Mould, clumping, a musty cellar note or moving specks means bin it and wash the container before the next bag goes in; webbing or tiny beetles is a pantry moth or grain mite infestation that will reach your own flour if you ignore it.

Storing pet food properly costs nothing. Buy a slightly smaller bag, keep it in its own packaging, clip it shut, wash the bowl. Do that and the food your pet eats in week five is the food you paid for in week one.