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Re-using oil for deep frying


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#1 ElsieD

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Posted 11 April 2008 - 04:51 PM

I presently have a T-Fal deep fryer and so far have been using it only to deep fry potatoes (sweet and regular). If I were to start using it to fry say, chicken wings, can the oil then be re-used to deep fry something else? Or does deep frying chicken wings or, say, jalepeno poppers, mean that the oil must be discarded? I have never seen this adressed anywhere and would appreciate some input.

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#2 prasantrin

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Posted 11 April 2008 - 05:04 PM

There are many, many references (some of those are for resusing motor oil, but the bulk are for cooking oil) that can be found regarding re-using cooking oil. Basically you should consider what you're frying, and what you want to reuse the oil for. If you're frying french fries, then using the same oil for chicken won't be a problem. But if you fry fish, you might not want to use the same oil for french fries, because your fries will then taste like fish. Just use your best judgment.

#3 takadi

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Posted 11 April 2008 - 05:07 PM

Fried mars bars just aren't the same without that hint of fish!

#4 Chris Amirault

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Posted 11 April 2008 - 05:18 PM

Independent of the off-flavor issue, several authors (including Russ Parsons in How to Read a French Fry) explain that including some old oil is crucial to a good fry.
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#5 prasantrin

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Posted 11 April 2008 - 05:20 PM

Fried mars bars just aren't the same without that hint of fish!

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I think you have to be from the UK to appreciate fried mars bars with a hint of fish. :blink: :biggrin:

#6 Dave the Cook

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Posted 11 April 2008 - 05:24 PM

Chicken wings in particular present a strange issue. When I've deep-fried them, I end up with more liquid in the fryer than when I started. I'm guessing that the added volume is a mixture of rendered fat and collagen. I've never reused that oil, on the assumption that if it's got gelatin in it, it's not going to behave like pure oil with just a few impurities.

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#7 cricklewood

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Posted 11 April 2008 - 09:43 PM

In the restaurant we re-use the frying oil regularly, I don't see why you couldn't apply this to home use as well, the volume is smaller so I can imagine it accumulating gunk faster but then again, restaurant fryers can see so much action that oil needs to be changed regularly. When using vegetable oil I find that indeed new oil doesn't quite behave the same it takes a while before it gets the sweet spot and then moves from the sweet spot to just being dark and nasty. I have never tried to hold back some oil from the old batch, I assume if you avoid sediment this could do the trick. A trick is once the oil is cooled down, filter it to catch any spices, gunk , tempura/batter bits that have accumulated in the fryer. tha way you are not burning all this stuff up on the next run.

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#8 K8memphis

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Posted 12 April 2008 - 06:40 AM

I've read that frying a potato after frying something flavorfull like fish or chicken will remove the residual flavor. I've never tried it. I don't deep fry fish but there is the idea.

#9 pounce

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Posted 12 April 2008 - 07:26 AM

http://www1.umn.edu/..._every_day.html

Basically:

University researchers have found that a toxic compound known as HNE, which has been linked to heart disease and stroke, builds up steadily in intermittently heated oil for up to five hours at frying temperature.


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#10 Raoul Duke

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Posted 12 April 2008 - 12:56 PM

I have two containers for oil storage. One is clean and used to accept the oil after use. Whe the oil is poured into the fryer the original container is then cleaned of the residue on the bottom and rotated for use next. What has worked extremely well for me is to fry a large piece of ginger, sliced in half lengthwise, after frying anything and before storage. I'm usually pretty pessimistic about such things, but geez, it seems to work. I think this tip appeared in Gourmet magazine last year.
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#11 dougal

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Posted 12 April 2008 - 01:17 PM

Independent of the off-flavor issue, several authors (including Russ Parsons in How to Read a French Fry) explain that including some old oil is crucial to a good fry.

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Any chance of an 'executive summary' as to why?
And whether "a good fry" means more than a tasty one?



http://www1.umn.edu/..._every_day.html

Basically:

University researchers have found that a toxic compound known as HNE, which has been linked to heart disease and stroke, builds up steadily in intermittently heated oil for up to five hours at frying temperature.

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Interesting that that article is specifically referring to polyunsaturated oils.
Perhaps saturated fats might actually be wiser for deep frying?

And I can't make out what the significance of "five hours" might be in that report. Would that be the time for the HNE to reach a maximum? Or an important threshold concentration?
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#12 sandra

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Posted 12 April 2008 - 09:54 PM

If you are frying shellfish, re-using the oil may not be a great idea if the french fries you put in next will be eaten by someone allergic to shellfish - I have seen a reaction happen -
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#13 prasantrin

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Posted 12 April 2008 - 10:06 PM

http://www1.umn.edu/..._every_day.html

Basically:

University researchers have found that a toxic compound known as HNE, which has been linked to heart disease and stroke, builds up steadily in intermittently heated oil for up to five hours at frying temperature.

View Post


The study is for soybean oil in particular, and oil taken to 365F. There is no mention of other types of oil, except to extrapolate the results to include "oils that are highly unsaturated and contain linoleic acid" (but no further experiments have been done to include those other oils), nor does it mention results for frying at lower temperatures, such as 350F (which a lot of recipes call for).

#14 takadi

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Posted 12 April 2008 - 10:28 PM

http://www1.umn.edu/..._every_day.html

Basically:

University researchers have found that a toxic compound known as HNE, which has been linked to heart disease and stroke, builds up steadily in intermittently heated oil for up to five hours at frying temperature.

View Post


The study is for soybean oil in particular, and oil taken to 365F. There is no mention of other types of oil, except to extrapolate the results to include "oils that are highly unsaturated and contain linoleic acid" (but no further experiments have been done to include those other oils), nor does it mention results for frying at lower temperatures, such as 350F (which a lot of recipes call for).

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Does that mean saturated fats like lard are more stable for higher frying temperatures?

#15 Chris Amirault

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Posted 13 April 2008 - 06:06 PM

Independent of the off-flavor issue, several authors (including Russ Parsons in How to Read a French Fry) explain that including some old oil is crucial to a good fry.

View Post

Any chance of an 'executive summary' as to why?
And whether "a good fry" means more than a tasty one?

View Post

It's about more than taste. From the book, p 13-4:

Have you ever noticed how something fried in absolutely fresh oil never completely browns? In fact, it may not cook through at all. ... [F]rying is essentially a drying process. When a piece of food is dropped into hot oil, the heat evaporates any moisture on the outside of the food. Since the food is surrounded by oil, the moisture forms a very thin barrier between the oil and what is being fried. Fresh oil can't penetrate that barrier.

Fortunately, some of the by-products of the breakdown of oil are chemical compounds called soaps. ... The chemical soaps created in the frying process ... penetrate the water barrier and bring the oil into direct contact with the food being cooked, allowing both browning and thorough cooking. For that reason, old-time cooks always saved a ladleful of oil oil to add to the fresh batch when they fried foods.


Later, Parsons suggests about 1 T old oil per cup of fresh oil. I just dump a glug of old oil into the fryer/dutch oven before adding the new stuff. It really works: the difference in crispness in particular is remarkable.
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#16 FjornF

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Posted 22 January 2010 - 01:53 AM

To expand on what Chris said, some soap is good, too much soap is bad (allows to much oil to penetrate through the food making it greasy). Interestingly alot of Donut Shops do not worry about over saponification because they are continuously adding more fat the replace that which was been absorbed by their baked goodies.

Joe Pastry on the subject

I think there is not yet a consensus on if reusing oil is healthy. Does anyone have good information on this? From the article about soybean oil:

"Whether at home or in a restaurant, one should not reuse oils that are highly unsaturated and contain linoleic acid because they form HNE and related compounds," says Csallany. "Perhaps the best advice in general is to eat only limited quantities of fried foods."

Interesting, sounds like another compelling reason to switch back to animal fats. Ill take it.

#17 John Rosevear

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Posted 22 January 2010 - 06:20 AM

Later, Parsons suggests about 1 T old oil per cup of fresh oil. I just dump a glug of old oil into the fryer/dutch oven before adding the new stuff. It really works: the difference in crispness in particular is remarkable.


Seconded. And while I'm not sure the science actually holds for this, I have noticed that if I don't have used fry oil handy, a glug of bacon grease in the fresh (I use corn or peanut) oil seems to do the job.
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#18 eternal

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Posted 22 January 2010 - 10:57 AM

I reuse oil. I have a gallon of peanut oil that I would fry anything but stuff from the sea in. After I'm done, I strain it and freeze it. Still smells fine. When it gets to the point that it doesn't smell good, I would throw it out and start over. For the home cook, tossing a gallon of peanut oil every time I used it would make frying too expensive. If restaurants can use oil 100 times a day for a week, I don't see why I can't use it once every 3-4 weeks for 6 months...

#19 IndyRob

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Posted 22 January 2010 - 01:26 PM

Someone on another site recommended the T-Fal Ultimate EZ Clean Pro Fryer. It appears to be unique in that it will automatically (?) filter the oil after use and then you can easily break it down and throw everything but the heating element into the dishwasher. Anyone have any experience with these?

http://www.t-falusa....Z Clean Pro.htm

#20 Chris Amirault

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Posted 22 January 2010 - 03:17 PM

Funny this should bump up. I fried about 10 lbs of potato, sweet potato, taro, and other root chips for a New Years party and then bottled up the oil the next day. Last week, I sniffed it and it seemed completely neutral, so I just used the entire bottle, adding only a bit of fresh oil to top it off. The 10 lbs of curried chicken I then fried was among the best I've ever had -- and, again, had that shattering crust you die for. The oil now is spent, I think, and tastes of the curry powder and chicken.

(BTW, I don't always prepare 10 lbs of food at a time. Just sayin'.)
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#21 mgaretz

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Posted 22 January 2010 - 10:23 PM

Someone on another site recommended the T-Fal Ultimate EZ Clean Pro Fryer. It appears to be unique in that it will automatically (?) filter the oil after use and then you can easily break it down and throw everything but the heating element into the dishwasher. Anyone have any experience with these?

http://www.t-falusa....Z Clean Pro.htm


I have the "Emeril's" version of this fryer and I love it. Once the oil has cooled it automatically drains and filters into it's storage container. I put that in the fridge and reuse the oil 10-15 times (I don't fry any fish) topping up with fresh oil when necessary. We don't deep-fry all that often so the oil can be in the fridge for months between uses. So far no problems at all.

#22 jsmeeker

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Posted 23 January 2010 - 09:53 AM

Timely topic for me, too.

Last weekend, I wanted some Buffalo wings to eat while watching football. I bought a gallon of peanut oil and used about 2/3 of it to fry up with wings. I strained it into another container and put it in the fridge. On Thursday, I used that oil to make some potato chips. Last night, I used the oil to make fried catfish and hush puppies. Everything was really fantastic on the second and third fry session. I think the potato chips were the best I had ever made. And the fish and hush puppies turned out great.

I strained out the oil from last night's session, though probably not as well as I could have. I should have used some cheesecloth in my fine double mesh strainer. This oil is back in the fridge. Can I use it again? I DID cook some fish in it, so should I only use it for fish again?

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#23 judiu

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Posted 23 January 2010 - 10:50 AM

Timely topic for me, too.

Last weekend, I wanted some Buffalo wings to eat while watching football. I bought a gallon of peanut oil and used about 2/3 of it to fry up with wings. I strained it into another container and put it in the fridge. On Thursday, I used that oil to make some potato chips. Last night, I used the oil to make fried catfish and hush puppies. Everything was really fantastic on the second and third fry session. I think the potato chips were the best I had ever made. And the fish and hush puppies turned out great.

I strained out the oil from last night's session, though probably not as well as I could have. I should have used some cheesecloth in my fine double mesh strainer. This oil is back in the fridge. Can I use it again? I DID cook some fish in it, so should I only use it for fish again?

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#24 jsmeeker

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Posted 23 January 2010 - 11:53 AM

hmmm OK. I smell it and it smells like oil. But I am not really sure if it's a BAD smell. Sure, it doesn't smell like the stuff in the bottle that hasn't been used for anything, but I am not entirely clear what the standard is here. In the past, I frequently would use cooking oil once. But that gets expensive, especially when you use something like peanut oil.

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#25 David A. Goldfarb

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Posted 23 January 2010 - 01:08 PM

I find that after I fry any kind of fish in oil, I need to replace the oil. Heat it up and make some French fries, and I bet they'll taste like catfish.

What I've been using for frying lately is a Griswold cast iron Deep Fat Fryer (#1003), and I've been really pleased with it. Fortunately these aren't particularly collectible, so you can find them on eBay for around $40 without the original basket or $60 with. The shape is just right, so there isn't excessive spatter with a half-full pot of oil, and the heat retention of cast iron helps maintain the temperature when the food is added to the oil, and it's not another appliance vying for counter space. I've been keeping it ready to go with beef fat in the fridge, and I filter the oil through a strainer lined with paper towel as needed.

Edited by David A. Goldfarb, 23 January 2010 - 01:08 PM.


#26 nickrey

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Posted 23 January 2010 - 05:41 PM

After frying I always use a paper filter for my oil.

When opened up they are cone-shaped and fit into a large funnel sitting directly in the oil bottle.

It takes a while for the oil to run through but I find I can use the oil many times before replacing it.

Jeff, if your oil smells at all like fish, I wouldn't use it for anything other than fish and chips.

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#27 agray

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Posted 23 January 2010 - 06:04 PM

This is indeed timely, especially the comments about possible issues with polyunsaturated oils and reuse, as I've been starting to research cooking with animal fat instead of vegetable oil. It's still early days (I'll be rendering lard next week), but here's what I read recently in Jennifer McLagan's "Fat":

Lard is very low in polyunsaturated fatty acids, so it is very stable when heated and much slower to oxidize and turn rancid than highly polyunsaturated oils are... all fat degrades with time, and heat makes this happen even faster. The fat should be filtered after each use, cooled and then refrigerated. It's probably not wise to reuse the fat more than three times.


Now this is lard she's referring to - I wouldn't likely refrigerate peanut oil etc, but from what I've been reading it seems that it might not be a great idea to keep vegetable oil around through many fryings due to the oxidation resulting from frying.
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#28 Starkman

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Posted 29 January 2010 - 06:05 PM

I think one thing to keep in mind is that the flash point of oil is lowered after just one fry. Now if you're only frying at, say, 350-375, you'll probably be safe. But for super-high temps, I'd be leery of doing so more than a few times..

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#29 LindaK

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Posted 14 January 2011 - 05:57 AM

I've decided to join the deep frying club too, so this is all helpful information. But I still have a few questions about reusing oil.

It sounds like filtering is imperative. what do you use--cheesecloth? coffee filters?
what type of container do you use, or does it not matter? can i recycle a milk jug, for example?
do you store your oil at room temp, in the fridge, or in the freezer?


 


#30 gfweb

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Posted 14 January 2011 - 08:04 AM

I store mine strained, but not filtered, at room temp in a big plastic jug. I've not had problems, but I can't say that I know that this is the best method. It would be a good study for a someone with access to a lab. What changes exactly make for "bad" oil? What foods make oil spoil? How many uses with various foods until the oil is no good. How much time can the stuff sit at room temp etc etc. Mc Donald's has the data I'm sure.