You can always tell when tomatoes have gone yucky or milk is well past its use-by date. But what about food in jars and tetrapaks or dairy produce?

Don't think that some foods last forever just because you can't see the rot.

Dr Charlotte Grayson Mathis, a specialist in internal medicine, shared these tips with WebMD (www.webmd.com). This is how long you should store the following:

Baby food: Unopened: one year; opened: two to three days in the fridge.

Butter: In the fridge: three months; You can store extra sticks in the freezer for up to a year.

Chilli sauce: Unopened: one year; opened: one month in the pantry, longer in the fridge.

Fresh eggs: Uncracked: two to five weeks in the fridge; cracked: use immediately.

Jams: Unopened: one year; opened: one year in the fridge. Best to store jam in the fridge, even before opening.

Juice: Unopened: one year; opened: one week in the fridge.

Ketchup: Unopened: one year; opened: one month in the pantry, longer in the fridge.

Mayonnaise: Unopened: two to three months; opened: two months in the fridge. Be sure to refrigerate after opening and never leave out of the fridge for more than two hours.

Mustard: Unopened: two years; opened: six to eight months in the pantry or the fridge.

Olives: Unopened: one year; opened: one to two months in the fridge.

Peanut butter: Unopened: six to nine months; opened: two to three months in the pantry, longer in the fridge.

Pickles: Unopened: one year; opened: one to two months in the fridge.

Salad dressing: Unopened: 10 to 12 months; opened: three months in the fridge.

Sour cream: Unopened: two weeks in the fridge; opened: two weeks in the fridge.

Tomato paste: Unopened: one year; opened: five days in the fridge.

Vegetable oil: Unopened: six months; opened: one to three months. For best results, store opened vegetable oil in the fridge.

This story was first published in Mind Your Body, The Straits Times, on Oct 2, 2008.