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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.

Thank you.

#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.

View Post

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 tkassum

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Posted 29 November 2008 - 08:40 AM

Dear eGulleters,

Thanksgiving is now over, for which I give thanks. My thoughts can now turn from highly technical subjects (like “how do I make something dry and tasteless into something moist and flavorful using only an oven?”) to more practical matters - like deep-frying!

Deep frying is a mysterious black art for those of us who are unfamiliar with it. There is very little practical information on the internet about it. My Google searches returned plenty of information on deep-frying turkeys, but to my mind starting there is the equivalent of a reverse slam-dunk before you learn how to do a lay-up. My beloved Cook’s Illustrated mentions it fleetingly from time to time before returning to standard fare (“Nine Course Meal in 30 Minutes”, etc).

My first experiments in home deep frying actually did take place over this year’s Thanksgiving, a holiday which is otherwise linked in my memory with dessicated turkey and sad, broken sauces. My fiancee and I made homemade doughnuts and some potato skin crisps. Strangely, after I fried my potato skin crisps (which were very tasty), I sniffed the oil and it had an unmistakable fishy flavor. But there was no sniffable fishiness before I fried the potato skins.

Let’s discuss!

1) What’s the best oil for deep-frying, anyway? People say peanut oil – but where and how does one buy gallons of this stuff (especially in New York)?
2) And why does it sometimes turn fishy? What can one do to prevent this?
3) How many times do you reuse the oil before you pitch it?
4) How can you pitch it in a planet-friendly fashion?
5) What are your favorite things to deep-fry?
6) Any tips, tricks, etc to avoid blowing up the house and to encourage optimal fryage?

Thanks,
TK

#17 Ruth

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Posted 29 November 2008 - 11:16 AM

You can buy the very best peanut oil by the gallon at any Chinese supermarket. It comes from Hong Kong .
I have never known peanut oil smell fishy but canola oil heated to high temperatures most certainly does. It apparently is loaded with omega 3. I never use it for frying or even for any kind of cooking.
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#18 tkassum

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Posted 29 November 2008 - 03:34 PM

Hi Ruth

Thanks for your helpful reply.

Funnily enough we rolled on down to Canal Street today and went to New Kam Man marketplace. In addition to ninja-themed mugs we also bought a gallon of "Knife Brand" peanut oil. Looking forward to using this going forward.

I think you're dead right about the canola oil. It is probably also a function of degradation at temperature - we used canola to cook doughnuts at 325 degrees, which were not at all fishy, but when we raised the temperature to 360 degrees for potato skin crisps, the fishiness came out.

Funny how food science actually has applications in real life!

#19 SeanDirty

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Posted 01 December 2008 - 08:40 AM

1) What’s the best oil for deep-frying, anyway? People say peanut oil – but where and how does one buy gallons of this stuff (especially in New York)?

BEEF TALLOW (what McDonalds used before it went all health conscious) Then second place peanut oil.

2) And why does it sometimes turn fishy? What can one do to prevent this? DONT FRY FISH.... heheh only way to avoid it... or actually i think you may refer to the oxidation of the oil, which it does go bad and rancid and will emit that sort of smell after extended use, or excessive heat... Which oil can burn and evaporate... and go RANCID!!

3) How many times do you reuse the oil before you pitch it? Thats relative... if you fry one thing a day, it could go alot longer then a few days / weeks... usually you can go by clarity, taste, just like meat... if it seems bad it probably is...


4) How can you pitch it in a planet-friendly fashion? Put it in your eco friendly car.... or recycle it... there are filters out there that can help you reuse your oil Many times over...


5) What are your favorite things to deep-fry? The real question is what cant you deep fry... Ive tried everything... But battered seafood is good... Akras... with a spicy mayo..


6) Any tips, tricks, etc to avoid blowing up the house and to encourage optimal fryage? Um.... unless your using gasoline... or dumping ice or water into your fryer... i think you should be fine... DONT LEAVE IT UNATTENDED...
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#20 RAHiggins1

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Posted 01 December 2008 - 09:04 AM

1) What’s the best oil for deep-frying, anyway? People say peanut oil – but where and how does one buy gallons of this stuff (especially in New York)?
2) And why does it sometimes turn fishy? What can one do to prevent this?
3) How many times do you reuse the oil before you pitch it?
4) How can you pitch it in a planet-friendly fashion?
5) What are your favorite things to deep-fry?
6) Any tips, tricks, etc to avoid blowing up the house and to encourage optimal fryage?

Thanks,
TK

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1) /agree SeanDirty; Beef fat rocks the deep fryer. Peanut is #2.
2) Change oil after frying fish. Sean and I are scarily similar....
3) See SeanDirty #3
4) I save the oil by frezzing it until the container is full, then I'll take it to a local restaurant and ask to add it to their receptacle outside. Alternatively, you could give it to a bio-fuel geek driving his diesel mercedes 1500 miles on a gallon of the stuff.
5) You can deep fry anything, ask the Scots! Fish, potatoes, wings, any number of croquettes, onion rings, it just goes on and on..
6) a.) Pay closer attention to your fryer. You need one that recovers heat quickly and controls heat efficiently. Common mistakes are to put too much in at one time which lowers the heat too much, causing the food to absorb more oil and make it greasier. A quick recovery of cooking temperature helps this greatly. Electric models just don't have the BTU's and Gas models are expensive and usually Industrial. I use a Cast Iron Dutch oven at home and wing it. I'll turn the burner on high when I put food in and reduce heat to ideal temp as the oil recovers.
b.) Allow the food to drainly thoroughly over the fryer. Oil cools down quickly and will stick to the food if you fish food out and put it on paper to drain and then you have greasy food staying in contact with greasy paper as well.
c.) Ideal temp for pretty much anything is 365ºF.
d.) Food continues to cook out of the oil, Golden Brown will darken further after you take it out.

Edited by RAHiggins1, 01 December 2008 - 09:07 AM.

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#21 Pam R

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Posted 01 December 2008 - 09:15 AM

2) And why does it sometimes turn fishy? What can one do to prevent this?

Are you asking why does canola oil smell fishy even when you don't fry fish?

Apparently for some people, canola oil does give off a fishy odour all on it's own. I've never experienced it, and I use canola often for frying.

#22 nickrey

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Posted 01 December 2008 - 07:39 PM

I filter my frying oil through a disposable fry oil filter cone after each use. This removes a lot of taste contaminants and seems to increase its longevity. This doesn't apply to oil used for frying fish, which probably needs to be recycled much sooner.

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#23 HowardLi

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Posted 01 December 2008 - 07:46 PM

A coffee filter with disposable paper filters might do the trick as well.

#24 Chris Amirault

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Posted 01 December 2008 - 08:19 PM

Some deep frying tips I've learned hereabouts and elsewhere:

Toss in old oil whenever you're using new oil; 10% is a good amount. It helps to crisp up the food. You want a little breakdown.

Use your ears. Deep frying is about oil and water; when the latter burns off in the former, the sound changes from a bubbly rumble to a slight hiss.

Oil temperature drops 50-75F when you put in a batch of stuff, so heat the oil higher than you want it.
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#25 SeanDirty

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Posted 02 December 2008 - 09:55 AM

I dunno about the old oil thing... The way i see that is... if i had old ground beef why would i throw it in with new ground beef... just because its aged it doesn't mean its better...

Oil breaks down from Light abuse, as well as oxidation, and age... Chefs work so hard to have the best product and cooking tools, and of course quality of ingredients... oil being one of them as well... I just dont understand why you would want to add old oil to good oil...

Could you explain how Alittle breakdown in new oil by adding old is good....?? What could the benefit be?
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#26 HungryC

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Posted 02 December 2008 - 12:25 PM

Regarding oil disposal: it is a simple matter if you're a home cook with a yard or compost heap. Vegetable oil is a natural product; it will biodegrade quickly. Dig a hole in the yard or corner of the compost heap, pour in the cooled oil, and forget about it. n.b., if you have a dog, this won't work, unless it is a very well-behaved or finicky dog. The poor dog can get very sick from eating greasy compost (don't ask).

I'm partial to peanut or soybean oil; I abhor the odor of canola oil, which is intensified by frying (to my nose, anyway). Practically every supermarket & sporting goods store in the Deep South carries peanut oil in huge containers (up to 5 gallons), so it's not exactly hard to find 'round here.

How long the oil lasts depends on what you're frying--some things gunk it up faster than others. Beware that the flash point of oil decreases as the oil ages/breaks down--old oil is more likely to catch fire than the fresh stuff.

Hmm--favorite things to fry, a potentially very long list: beignets, onion rings, leftover boiled potatoes, tempura-battered veggies, fresh fish, oysters, shrimp, bread dough, battered oreos, chicken wings, bone-in chicken, natchitoches meat pies, samosas, pakoras, breaded blue crab claws (already cracked)...but the hands-down favorite at my house is potatoes. Properly made fries are a thing of wondrous beauty.

#27 Chris Amirault

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Posted 02 December 2008 - 02:38 PM

Could you explain how Alittle breakdown in new oil by adding old is good....?? What could the benefit be?

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It's the soaps, I tell you. Back here I quoted Russ Parsons from his How to Read a French Fry, the relevant selection of which follows:

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.


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#28 RAHiggins1

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Posted 03 December 2008 - 05:03 AM

Could you explain how Alittle breakdown in new oil by adding old is good....?? What could the benefit be?

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It's the soaps, I tell you. Back here I quoted Russ Parsons from his How to Read a French Fry, the relevant selection of which follows:

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.

View Post


I learned on "Beakman's World" (saturday morning kids science program) that soaps work by breaking down water's surface tension, there by making water wetter. Now I'm wondering if it's the moisture barrier on the Fry or the oil that is effected by the soaps?

I'm going to say soaps effect the water making it evaporate more efficiently.
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#29 steverino

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Posted 23 August 2009 - 01:39 PM

I used some canola oil a few weeks back to fry some taters and chicken- y'all think it's safe to fire up again? Obviously it's going to be brought up to temp high enough to kill any bugs... I smelled it, and it seems ok.. any input would be appreciated.
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#30 Chris Amirault

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Posted 23 August 2009 - 02:11 PM

I always have several quarts of used fry oil in the basement, never refrigerated. We're all still here. :wink:
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