An opened bag of cat food is good for 8 weeks, and 6 weeks if the kitchen sits above 25 °C in summer. Once storage temperature passes 25 °C, the fat in kibble oxidizes roughly 2 times faster, which is why a 4 kg bag can smell fine and still cause a refusal or a loose stool in week 7. Keep the food sealed, dark and between 15 and 21 °C, and write the open date on the bag with a marker the day you cut it.
The 8-week clock starts when you open the bag
Kibble fat sits at 8 to 20 percent of dry matter, and that fat is the part that turns. Oxidation starts the moment the bag meets air, and it does not stop when you clip the top; it only slows. A 2 kg bag fed to one cat at 60 g a day lasts 33 days, comfortably inside the window. A 7 kg bag at the same intake lasts 116 days, which is 8 weeks plus 60 days of decline. Buy the bag your cat finishes in 6 to 8 weeks, not the one that costs least per kilo.
Temperature: 25 °C is the line, 15-21 °C is the target
Every 10 °C above 20 °C roughly doubles the rate of fat oxidation, so a bag stored at 30 °C in a garage ages about 2 times faster than one at 20 °C and 4 times faster than one at 10 °C. Humidity matters alongside it: above 60 percent relative humidity, kibble picks up 1 to 3 percent moisture, and past 0.65 water activity mold has a foothold. The table below gives usable weeks for the same 2 kg bag in 6 real storage spots.
| Storage spot | Temperature | Humidity | Usable after opening |
|---|---|---|---|
| Dark cupboard, air conditioned | 18-22 °C | 45-55% | 8 weeks |
| Kitchen shelf near stove | 26-32 °C | 50-60% | 5-6 weeks |
| Garage in summer | 30-38 °C | 60-75% | 3-4 weeks |
| Fridge, sealed | 4 °C | 70-80% | 6 weeks, condensation risk |
| Freezer, sealed | -18 °C | n/a | 6 months |
| Opened can or pouch | 4 °C | n/a | 3 days |
%DM math: why fat is the fragile part
Read the guaranteed analysis on dry matter, not on the bag as fed. A wet food labelled 10 percent protein and 78 percent moisture is 45 percent protein DM, while a dry food labelled 32 percent protein and 8 percent moisture is 35 percent protein DM, so the wet food is the denser one. Fat behaves the same way, and fat is what oxidizes into peroxides and aldehydes that cats smell long before you do. A food at 20 percent fat DM holds about 200 g of fat per kg, and 200 g of fat with even 2 percent oxidation produces enough off-aroma to make a cat walk away after 2 sniffs.
Sealed, dark, and keep the original bag
Kibble bags are built with a metallized or EVOH barrier layer that blocks oxygen and light better than most plastic tubs. The workable routine is to keep the food inside its original bag, squeeze the air out, fold the top twice over 5 cm, clip it, and stand the bag inside a 5 to 10 L opaque container with a rubber gasket. Clear glass jars on a sunny counter are the worst choice: light drives riboflavin loss and photo-oxidation at the surface within 2 to 3 weeks. A 2 kg bag needs 1 oxygen absorber, replaced every 30 days, and never a moisture absorber in the same container, since drying kibble only makes it brittle.
Fridge or freezer: the 2 categories that qualify
Only 2 things belong in the cold. First, opened wet food: transfer the remainder to a lidded glass container, refrigerate at 4 °C, and use within 3 days, warming to 30 to 37 °C before serving so the cat actually eats it. Second, portioned raw or home-cooked food: freeze at -18 °C for up to 3 months, thaw in the fridge over 12 to 24 hours, and never refreeze. Dry kibble does not qualify for the fridge. Each open-close cycle condenses moisture on cold kibble, adding 1 to 3 percent water per week, and a bag that goes in and out for 8 weeks ends up soft, moldy and refused.
Recalls and the lot number you will need
Keep the bag, or at least photograph the lot code and best-by date before you bin it, because a recall notice names a lot and a date range, not a product name alone. Check recall lists every 2 to 4 weeks, and if a bag is named, stop feeding within the hour rather than finishing it. Symptoms to act on: vomiting 3 or more times in 24 hours, refusal for 24 hours, or blood in the stool. Storage mistakes and contamination look identical from the outside, so keep 1 opened bag at a time and note the date you started it. See food storage and recall practice for the lot-code routine, and opened wet food storage for the 3-day rule in detail.
Signs a bag has turned
Four checks in 30 seconds: smell the bag from 15 cm, and a sharp paint-like or crayon note means oxidized fat; rub a pinch of kibble between your fingers and look for greasy dust on more than 5 percent of pieces; check for clumping, which means moisture entered; offer 3 pieces and watch whether the cat sniffs twice and walks away. Cats detect rancidity earlier than humans, so a refusal from a cat that normally eats the food is data, not fussiness. Never mask a turned bag with warm water or a topper.
A 4-step storage routine
- Write the open date on the bag with a permanent marker, and put the same date in your phone calendar plus 8 weeks.
- Store at 15 to 21 °C, dark, sealed with the air pressed out, inside an opaque container with a gasket.
- Buy 2 kg bags if your cat eats under 80 g a day, and never keep 2 opened bags at once.
- Every 4 weeks, check the recall list and the calendar; past 6 weeks, plan to finish the bag within 14 days.
What a 1 °C change is worth
Moving a bag from a 30 °C garage shelf to an 18 °C cupboard buys roughly 4 extra weeks of usable life on the same food, which for a 100 g a day cat is 2.8 kg of kibble that does not get binned. Over a year that is 1 to 2 bags, or 30 to 80 dollars, saved by moving a container 3 m. If the pantry itself runs above 25 °C in July, buy smaller bags for those 8 weeks instead of installing a fridge for the food.
Terms mentioned in this article
Frequently asked
Can I freeze dry cat food to make it last longer?
You can freeze a sealed bag at -18 °C for up to 6 months and it will slow fat oxidation, but you must let it come to room temperature before opening, still sealed, so condensation forms on the bag rather than on the kibble. Once opened, the 8-week clock starts and it should stay out of the fridge.
Is a plastic storage bin better than the original bag?
Not on its own. The original bag usually has a metallized barrier that blocks oxygen and light better than a plain tub, so keep the kibble inside the bag and put the closed bag inside the bin. A clear container on a bright counter is worse than the bag alone, because light drives oxidation at the surface.
How long does opened wet food last in the fridge?
Three days at 4 °C in a lidded glass container, and some vets accept 5 days for a pate with no gravy. Warm it to 30 to 37 °C before serving, because most cats refuse food straight from the fridge, and discard anything that has been out at room temperature for more than 2 hours.