GASTRONOMER.ORG

By Ross Goldenberg
November 9, 2011

Frying your turkey this thanksgiving? Whether you’re a first-timer or a veteran of this fun, dangerous, quick and most tasty method, there’s one element of the deep fried turkey that nobody ever talks about.

I’ve read dozens of articles about the perfect way to fry a Thanksgiving turkey and dozens more about the not-so-perfect way to endanger yourself, your house and your friends while frying your turkey. (My most favorite method for frying my turkey is the Alton Brown Rig and my most favorite source for jaw-dropping what-not-to-do videos is YouTube.)

But everything I’ve ever read about a deep fried turkey seems to stop at the cooking part or, sometimes, the eating-the-leftovers part. Having deep-fried my turkey for several years now (see slide show), the conundrum I’m always stuck with is what the heck to do with 8 or more gallons of leftover cooking oil.

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It’s never a good idea to pour it down the drain or dump it in a sewer or storm pipe. Such an action can leave a nasty residue in your pipes and possibly contaminate your soil. Some articles I’ve read suggest that you freeze used cooking oil in an airtight container to solidify it, making it less messy, and then dispose of it in your trash. I guess if you contain it similar to the way radioactive waste is buried, it can certainly sit in a landfill for thousands of years.

But after spending almost as much money on oil as I do on my turkey, I’m not about to dispose of my cooking oil until the stuff has no useful life left. And, in my humble opinion, a vat of hydrogenated oily goodness that has merely touched the life of one piece of meat for only a few minutes has a long future ahead of it.

The first year I fried my turkey, I think I spent the months between Thanksgiving and St. Patrick’s day frying just about every food I could get my hands on just to make use of as much of the stuff as I could before it went rancid. I was able to use a significant amount of the oil before it went bad, but I’m not so sure it was the healthiest thing to do. Don’t get my wrong, I love my deep fat fryer and use it regularly at home. But the amount of oil I was challenged to use in the 3 months fulfilled my usual fried food quota for a year. Plus, after about two months, the oil was really not that fresh anymore and it was starting to affect the taste of my hush puppies.

So two years ago, I took on the challenge in a different way – attempting to figure out:

1. How to increase the longevity of the oil
2. If possible, scientifically measure the rate at which the oil went rancid (or at least quantify how rancid it was)

The ideas was that if I could stretch the consumption of my Thanksgiving oil across a 12-month period instead of a 3-month period, I’d feel I would have done my oil (and my wallet) justice. If I was successful, I’d be able to rationalize the oil purchase the following year.

So began the process of the conservation of oil….

Cleaning the Oil

The first step in my experiment was to “clean” the oil. This is method is commonly recommended in preserving any fry or cooking oil. Whenever I deep fry foods and plan to reuse the oil, I take the following steps:

Filter the nasty bits out by passing oil through a cheesecloth

1. Let the oil cool to a temperature between room temperature and bathwater temp (80-100 degrees Fahrenheit). If you’re starting with cool oil (maybe because you forgot to clean it or were too focused on eating), that’s okay too. Just heat the oil slightly in your fryer or on the stovetop. This step will help with the filtering process.
2. Let the oil rest undisturbed for at least 5-10 minutes so the heavier particles fall to the bottom of your container.
3. Strain the oil through a couple layers of cheesecloth or a fine mesh sieve (or both). When doing this, try to agitate the oil as little as possible. I do this by using a coffee pot to scoop the oil out of the vessel it’s in and into the filter; pouring the oil directly from the giant vessel into the filter agitates the fry bits in the bottom and can get quite messy.
4. When there’s a cup or two of oil left in your original vessel, you’ll probably have a thick mixture of oil and fry sludge. Don’t try to pass this through your filter. Instead, discard it. You can discard it by using the method I mentioned earlier (sealing your oil in an air tight container) or mix it with spent coffee grounds and throw it in the trash.
5. Then, put a coffee filter in a funnel (if it’s cone shaped) or a strainer (if it’s cupcake shaped). Pass the warm oil through the coffee filter. Depending on how “dirty” your oil is, you may need to use several coffee filters. And if your oil starts to get cool, you may want to heat it slightly—the warm oil seems to pass through the filter quicker. Note that sometimes after frying I get lazy and skip this step. I’ve found that if you’re going to use your oil relatively soon (within a week or so) skipping this step is okay.

The Molecular Challenge

Once my oil was clean, I turned to my food scientist friends at the molecular gastronomy Google Group. Here’s the challenge I gave them:

1. Since contact with air increases the spoilage rate, might the life be extended significantly if the oil was stored in a vacuum bag? Alternatively, what if a heavy inert gas like nitrogen was put into the storage container to create a layer between the air and oil in the container? (This is sometimes done with nice wines to extend their storage life once opened—see www.privatepreserve.com.)
2. What if the used oil were spun in a centrifuge before storage? How might that affect the taste and shelf life of the oil? I see this as a critical step in “cleaning” used oil for the commercial production of biodiesel and have to assume that it would significantly reduce the solid particles left in the oil that might increase the spoilage rate.
3. Would storing the oil at very cold temperatures (i.e. in a deep freezer) significantly extend the life beyond storing it in a “cool” place?

I assume all three ideas above would extend the shelf life of the used oil somewhat, but I wonder how significantly the life would be extended? This leads me to another interesting question:

What scientific method might I use (other than smell and taste) to quantify when the oil has become rancid (or how rancid it is)? I’m not a scientist, but I presume the specific gravity of the oil will change over time as it goes rancid. But, again, I’m not sure how much the specific gravity will change; will it change enough for me to measure it outside of a lab setting? Finally, and most notably for the scientists out there, the ultimate question I am left with is:

Is it possible to re-refine the oil or separate the oil molecules that have started to break down in the cooking process with the ones that have not yet oxidized?

The overwhelming response I got can be summed up into four main points:

1. Oil goes bad primarily from oxidation, which generally occurs from contact with oxygen (air) and light (photo oxidation).
2. Lower temperatures slow down the speed of chemical reactions. Oil kept in the fridge goes bad at a sixth the rate of oil kept on the shelf. Presumably, oil stored in the freezer would go bad at an even slower rate.
3. There is no commonly used scientific way to measure the oxidation or rancidity of oil.
4. An oil-soluble antioxidant such as vitamin E or flax seed oil may slow down the oxidation process. Some commercial fry oils have a small amount of silicone added to them, which creates a film on the surface to help slow the oxidation, but the toxicity and adverse health effects come into question.

Given the points above, I decided to set up a year-long controlled experiment. Because the fourth point is a bit over my scientific head, I decided to stick with three variables in my experiment – light, air and temperature. I figured that the antioxidant additives might help but probably would only be a secondary way to preserve the oil, extending the life even further if any of my other experiments worked.

For my experiment, I created three samples:

1. A quart of oil stored at room temperature in a Chinese takeout container with moderate ventilation holes cut in the top.
2. A quart of oil stored at room temperature in a vacuum-sealed bag.
3. A gallon of oil stored in a vacuum-sealed bag and stored in a dark freezer (about -10 degrees F).Note that the first two samples were stored in my basement where they were exposed to a low to moderate amount of light. The third sample was kept in my mostly-dark freezer.

A failed attempt to measure the specific gravity of oil

When packing my samples I also attempted to measure the specific gravity of the oil. Specific gravity is a measurement of the density of a liquid. It’s commonly used in beer making, which is where I know it. I wasn’t sure if the specific gravity would change as the oil oxidizes but I was hopeful it would provide some meaningful scientific calibration of just how oxidized or spoiled the oil was. I quickly learned that measuring the specific gravity of oil (which is a lot less dense than water) using beer-making equipment just doesn’t work. Beer is largely water based and the specific gravity is extremely close to that of water, which is 1. Oil on the other hand is A LOT less dense and my tools were quite inadequate to measure the specific gravity of oil. So much for that angle!

So I resorted to two of the good ol’ five senses to measure how spoiled my oil was—smell and taste. If you’ve never smelled or tasted rancid oil before it seems there’s just no way to describe what it tastes or smells like. I scoured the Internet looking for accurate descriptions and really did not find anything close. The closest I got was that it smells like crayons. I also found people describe it as musty, similar to burning silicone, and the smell of old house paint. To me it tastes soapy—possibly because it’s only a step or two away from the process of saponification and could actually turn into soap if treated right. It’s also described to have a more greasy mouth feel than regular oil.

A well ventilated container of oil, which has a short shelf life

Based on the advice I got from my food-scientist friends, it seemed pretty clear to me that the oil in the Chinese food container would go rancid first, followed by that in the unfrozen vacuum bag. And finally the oil in the freezer would last the longest. (Since I felt pretty confident in my hypothesis, I also cheated and froze another 6+ gallons of oil in my freezer for use over the coming months.) The question remaining was what the differential would be.

I proceeded to smell and taste the first sample in the soup container every few weeks until it was clearly spoiled and unusable. Like most oil I’ve left out for a long time, it only took a few weeks to start to turn and was surely unusable between the 30 and 60-day mark. Once that went bad, I left the vacuum-sealed bag along for another 30-60 days and tested it. It was tasty as ever. Because I had so much frozen oil and by March was ready to do some more frying, I started digging into my stockpile of frozen oil. Not surprisingly, the frozen oil was as fresh as the day I had packed it. In fact, I continued to use the frozen oil for another year and a half and to this day have not been able to get my frozen oil to go rancid. And because I had sucked out all the air and moisture from the bag the oil does not get freezer burn or “wet inside.” Moreover, because I froze the oil in 1 gallon batches, when I’m ready to make use of my fryer, all I need to do is take a packet of frozen oil out, let it defrost until it’s semi-liquid and pour the pre-measured amount into my fryer. It couldn’t be simpler than that!

So what I have I learned through all of this? Here’s a summary of takeaways:

1. The first step in prolonging the lifespan of your oil is to clean out the nasty bits (solid chunks) as soon after frying as possible.

   

   Non-frozen oil samples were stored in my basement ceiling atop cold water pipes

2. When storing your oil, suck out as much air from the storage vessel as possible. Using a vacuum sealer is ideal, however if you don’t have one of those, you can also use a vacuum pump commonly used for preserving wine or add a food safe inert gas that is heavier than air (see www.privatepreserve.com).
3. To prolong the lifespan of your oil store it in the fridge or freezer. I used to shy away from buying oils in bulk. But with my little freezer trick, I can by a gallon of sesame oil from a restaurant supply place for about as much as I pay for two of those little jars in the ethnic section of my grocery store. I separate the gallon into containers that carry a 30-60 day supply and freezer them. I have yet to have bad oil after it’s frozen.
   

   A plethora of vacuum sealed oil ready to be stored

4. It’s still unclear how much light affects the rate at which oil oxidizes, but it’s pretty common knowledge that light is not a friend of oil. So store your oil in a dark place.

So now that you’re able to

preserve your oil indefinitely, you’re left with the burning question of what to do with it, right? Here are some final thoughts:

1. Fry more food! I use this exorbitant amount of oil to go on “frying binges” where I heat up the fryer on a Friday night and try to fry anything I can get my hands on before Monday morning. It turns into quite a fun challenge. My two favorite inventions that have come out of these fry-fests are fried matzoh balls for Chanukah (explained in my next post) and fried apples and honey for Rosh Hashanah. (The Jewish theme is just a coincidence.)
2. Craft some handmade soap. The process of saponification starts with oil and a very strong base such as lye. It calls to your fight club side and your Martha Stewart side at the same time.
3. Make an oil lamp. This might also be a good use for your slightly rancid oil as well, though I presume you’ll have to add perfumes or other scented additives to any oil that’s turning bad.
4. Fry some more food! Challenge yourself to figure out ways to take classics such as macaroni and cheese and create a fried version of it.
   

   A freezer with the bottom full of oil

Special Thanks To:

• Greg, my brother-in-law and Thanksgiving fry-daddy partner-in-crime.
• The guys in the Molecular Gastronomy Google Group, especially Scott Garrison, Derek Lindner, Roy and W Keith Griffith.
• Alton Brown’s turkey frying rig  and primer on how and why oil goes rancid, both from Good Eats

Tags: Deep Fry Turkey, Fry Turkey, Reuse Cooking Oil, Thanksgiving