We do a fish fry at our church every Friday during the season of Lent. Fish and French fries are fried in peanut oil. The man in charge of the event wants to use the oil that was used last year (and has been in the fryers since then). We are in Fort Lauderdale, Fla. (very hot weather; the oil was never refrigerated). I think the oil is unsafe or rancid. Please help me prove the oil needs to be replaced.
Clearly the gentleman in question wants to give up more than just meat he's also willing to sacrifice flavor. Perhaps he considers that a virtue. In our eyes, it's nearer a sin. Seriously, do you think we don't know better than to get in the middle of a boiling-oil argument among church members? We'll give you a little ammunition, but, as is often the case, the battle will still be yours.
We have been in touch with experts at the Peanut Institute and manufacturers of other types of vegetable oil, and although no one is willing to attach a hard-and-fast shelf life to their oil (once used), no one wants you to use year-old oil either.
The Peanut Institute folks say you should be able to reuse the oil until it develops a "rancid odor." Kept in a cool, dry place, it could last for six to eight months or longer.
The folks at Con-Agra, the conglomerate that markets Wesson-brand oils, say the issue is one of quality more than safety. Oil that has been used and then stored for a year will not approach the quality of fresh oil, they say. And the food you cook in it will reflect that loss of quality.
Oil as a cooking medium is a very fluid substance (pardon the pun). It undergoes a variety of changes as it is used, and indeed, changes in storage even before it is used. If it is overheated, the quality plummets. If it is contaminated with food particles, water, or oxygen, the quality is reduced and the smoke point drops, until you simply have to start over with fresh oil.
Russ Parsons, author of How to Read a French Fry* (Canada, UK), says scientists have identified five stages that cooking oils go through: break-in (so fresh that is has to be broken down a bit to fry well), fresh, optimum, degrading (on the way to spoiling), and runaway (dark, smelly, and prone to smoking).
What you want for your church fry-master is optimum oil. It is quite likely that what he has is a large quantity of degrading oil. A fishy aroma and flavor are indications that it is turning rancid.
It is a simple fact that people who deep-fry foods must be prepared to invest in new oil from time to time. Restaurants (and wise congregations) build that into their costs.
Perhaps your fellow member will accept a small compromise. Parsons says experienced cooks add a small amount of used cooking oil to fresh oil to speed the transition from the break-in or fresh oil stages to the optimum stage. Oil that is too fresh, he says, can't penetrate the water barrier surrounding most foods and doesn't do a good job of browning the food or cooking it through to the center. Adding a tablespoon of old oil for each cup of new oil, gives the mixture the slipperiness it needs to penetrate the water barrier and cook the food thoroughly.
To store oil for future use, strain out any impurities, put it in containers just large enough to hold it to minimize exposure to oxygen, and store it in a cool, dark place.
*The title of Parson's book, which covers many topics of food and cooking science, comes from the fact that you should be able to tell the quality of the cooking oil by looking at the food it produces that is, you can "read" a French fry to know if the oil is too new (white on the surface and raw inside), too old (dark, limp, and greasy), or just right (golden brown and crisp).