Capsules should keep oils safe from rancidity

Q. I read in your column about the tendency of oils to go rancid. Now I notice that my bottle of fish-oil gel capsules says the bottle should be kept tightly closed. Up until now, I've been putting my day's or even week's pill allotments into a small, open container. Sounds like this might be a problem. How long do you think fish-oil capsules can be exposed to the environment and still be effective and safe?

N.R., e-mail

A. Air and the oxygen it contains can react with, or oxidize, oils, and by doing so negate their beneficial qualities. The part of the oil that is most susceptible is a point of unsaturation, which makes a polyunsaturated oil, such as fish oil, especially vulnerable. Oils destroyed in this way are said to have gone rancid, and there is a particularly unpleasant smell to provide the unmistakable evidence.

Gel capsules come in various types and qualities and are designed to provide a barrier to protect their contents. Over time, there can be some gaseous interchange, but for all practical purposes, they will do the job. It is important to keep them out of the light -- especially sunlight, and away from any source of heat. I would stick with brands that use quality-control dating. You'll see a "best if used by" or a "use by" date stated clearly on the package.

Some products might use manufacturers' codes, and this can be a set of numbers and/or letters. If you prefer this product, you can always contact the manufacturer to decipher the code and get the expiration date equivalent.