Probably not much....there are many more factors that affect rancidity than just exposure to oxygen...like temperature how the oil was processed and stored before you got it, etc.

I think it would help. Factors such as high temperature work by hastening the oxidation reaction. If oxygen is excluded, temperature should be less of a factor.

Jim

Many things besides oxygen cause oxidation. Oxidation is defined as a substance losing electrons from the molecule. Smoked meats sealed air tight and frozen will become rancid.
Linda C

I remember seeing little packets in food packages which says something like "Oxygen Absorber, Do Not Eat".

Vacuum packing also helps.

Some more information to consider:

N.E.M Business Solutions 01823 680119
1.What is Rancidity. (rancid derived from "rancidus" the Latin for stinking).
Most any food can technically become rancid. The term particularly applies to oils. Oils can be particularly susceptible to rancidity because their chemistry which makes them susceptible to oxygen damage. When food scientists talk about rancidity, they are often talking about a specific type of rancidity involving oxygen damage to foods, and this type of rancidity is called "oxidative rancidity." During the process of oxidative rancidity, oxygen molecules interact with the structure of the oil and damage its natural structure in a way that can change its odour, its taste, and its safety for consumption.
Oxidation of fats, generally known as rancidity, is caused by a biochemical reaction between fats and oxygen. --------
Oxygen is eight times more soluble in fats than in water and it is the oxidation resulting from this exposure that is the primary cause of rancidity. ------------
In addition, rancidification can be decreased, but not completely eliminated, by storing fats and oils in a cool, dark place with little exposure to oxygen or free radicals, since heat and light accelerate the rate of reaction of fats with oxygen. ----------"

Therefore, possibly, Nitrogen replacement of air may be useful.

dcarch

Displacing the air from a container of oil with nitrogen WILL MOST DEFINTELY prolong the life of your oil. Rancidity comes from oxygen reacting with the double bonds of the unsaturated fats that are in that cooking oil. Keep the oil away from light (fluorescent and sunlight) and elevated temperatures too. For an EVEN LONGER shelf life keep it in the refrigerator. If it "waxes" or solidifies in the frig (like many olive oils do).....just allow it to warm to room temperature before use. Glass bottles are best for longest storage......some plastic bottles (like plastic storage and freezer bags) allow the exit/entrance of some gases. Foods kept in "storage" bags will get freezer burned or turn rancid because of this effect. "Freezer" type plastic bags are designed to lessen this effect.

Dan
Semper Fi-cus

Rancidity is highly desirable when it comes to cheese making.

dcarch

Thanks all. I got the idea because a bottle of flaxseed oil I bought recently said the bottle was filled "under a nitrogen blanket." I was thinking I might use it for oils I don't use too much and go rancid on me, like grapeseed. Seems a waste for wine. Easier just to drink it.

By the way, I bought the oil to try the cast iron seasoning method that Jimster linked a while back. My most successful seasoning effort to date - thanks Jim! It seems to have done a nice job on a carbon steel paella pan, too, but I haven't yet used the pan since doing it.

It is highly likely that the seasoning link that Jim referenced originated from my many posts on the care and seasoning of cast iron.

Grape-seed oil is a great seasoning oil simply because it has a rather high percentage of "unsaturated" fats in the oil. Seasoning is a polymerization type reaction and completely different than the rancidity reactions. The very BEST polymerization reactions for the seasoning of cast iron and carbon steel occurs at HIGH temperatures that are slightly above the smoking point of the oil. The problem you have with oils which have high unsaturated fats (i.e those that are considered healthy).....is they go rancid much faster and can thicken (especially if kept in metal can) to the point where the smoke point is significantly lowered. Keep the oil in a glass container, with a nitrogen purge/blanket, and in the refrigerator to DRASTICALLY improve its shelf life.

Dan
Semper Fi-cus

Rancidity is NOT desirable in cheese making. It's to be avoided at all costs.

Posted by lindac "Rancidity is NOT desirable in cheese making. It's to be avoided at all costs. "

However:

From Wiki:
----Rancidification is the chemical decomposition of fats, oils and other lipids (this degradation also occurs in mechanical cutting fluids). When these processes occur in food, undesirable odors and flavors can result. In some cases, however, the flavors can be desirable (as in aged cheeses)-----------

From University of Queens Land:

---- Lipolysis, the enzymic hydrolysis of milk lipids to free fatty acids and partial glycerides, is a constant concern to the dairy industry because of the detrimental effcts it can have on the flvor and other properties of milk and milk products. However, free fatty acids also contribute to the desirable flavor of milk and milk products when present at low concentrations and, in some cheeses, when present at high concentrations. ----

dcarch

I believe the "tang" sensation from acidity and from growing micro organisms is what is desired in cheese making. I agree with Linda, those flavor molecules have nothing to do with rancidity. Most of the fats in cheese are "saturated" fats which don't turn rancid unless they are first broken down.

Dan
Semper Fi-cus

Straight from the cheese maker....rancidity is NOT desirable...it can impart a bitter flavor even to well aged cheddars. It seems to occur in cheese that has too high a moisture content before being put to age.

As usual, nothing is ever absolute.

This also straight from the cheese maker, Wesconsin Cheese:

"Rancid
A term relating to flavors caused by lipase enzymes releasing fatty acids from butterfat. Some cheeses are not supposed to have flavors caused by fatty acids in high concentrations, such as Cheddar, while others, such as Romano, gain much of their flavor from the rancidity of fatty acids. ----"

dcarch

This from a site for small artesan type of cheese makers.
Romano has a decidedly soapy taste to me....
And please realize that unless you post something from a site which has some merit, what you copy and paste here is meaningless. You can likely find something on the web to support any position. My view of the undesirability of a rancid taste in cheese comes from quite literally looking over the cheesemaker's shoulder and taste testing batches at different stages of the aging process....while he was developing a marketable aged cheddar and an edam.

Lipase is an enzyme, in cheese making from a calf's digestive system which is added prior to adding the starter for creating a certain flavor in some cheeses. The cheeses that I know who use a lipase additive are Romano, Feta and provolone. the amount added and the time elapsed allow for a variation in that "soapy" flavor....on purpose. Sometimes the breakdown of the fats happens accidentally in cheeses not meant to have that soapy taste....

"rancid; rancidity
A rancid flavor or odor is caused by the decomposition of fat as lipase enzymes release fatty acids. This flavor can exemplify as a stale, somewhat bitter and spoiled quality. Oddly enough, a slightly rancid quality lends a few cheeses, such as romano, some of their distinctive flavor characteristics. On the whole, however, rancidity is decidedly a fault. In relation to cheese, the term rancid is also called lipase or soapy."

Of course your views are always fascinating and eye-opening:

> Your outright dismissal of oxygen depletion as a means of retarding rancid progression.

> Your opinion that the information from Wikipedia is meaningless.

> Your opinion that the information from Wisconsin Milk Marketing Board is meaningless.

> Your opinion that the study from the Queens Land University is meaningless.

I don't think anyone here is interested in you and I carrying on in pursuing the chemistry of lipase enzyme action in cheeses.

The only thing of interest to all is that cheeses taste pretty good. (Well, may be not blue cheese).

Isn't it interesting that the same bacterium responsible for the smell of many blue cheeses, is the same as the one that causes your feet to stink? :-)

dcarch

dcarch you are not only ill informed but also rude. This discussion began with your statement :
"Rancidity is highly desirable when it comes to cheese making.

dcarch"

To you really think that the same bacteria in Limburger is the SAME as that found on feet? Same genus but not the same species...like equating potatoes and deadly night shade.

Back to the subject at hand.....
You might gain some additional storage life by using as quirt of nitrogen and a tight cap, but you would have to re squirt every time you opened the bottle for a bit of oil....and then there's the cost factor, and as the bottle diminishes it takes more nitrogen to fill the space.
And as I said earlier, deterioration of oils doesn't ONLY take place by exposure to air....and a cold temperature slows any chemical reaction.
Linda C

Oils degrade in three ways........

Oil degrades from oxygen reacting with the double bonds contained in the unsaturated fats in the oil.....this chemical reaction makes the oil go rancid. Both sunlight and fluorescent lights can speed up this reaction. That is why oil in dark bottles can last longer.

Oil degrades from exposure to too high a heat....this causes large chain molecules to break down into smaller molecules. This thermal reaction then lowers the smoke point of the oil. This "thermal cracking" actually creates lighter molecular weight "unsaturates" that can turn rancid even faster than those molecules that were initially present in the Oil.

And finally oil degrades through polymerization reactions.....these chemical reactions will thicken the oil. Certain metals act as a catalyst and will make the oil get sticky or even gummy. The extent of polymerization that will occur depends on the temperature that it was exposed to and the type of metals that the oil was exposed to. Glass containers do not initiate these polymerization reaction like metal storage cans do.

If you fry anything in supposedly healthy Grapeseed oil using a stainless steel fry basket.....you MUST remove any oil splatter from that basket right away or you risk it polymerizing so fast that you will have a very hard time cleaning that basket. Likewise with any Grapeseed (or any high unsaturated fat cooking oil) grease splatter onto a chrome surfaced stove or other stainless steel surfaces. If you don't remove that oil spatter right away it will get very sticky and gummy and become harder to clean off.

The FACT remains that if you keep any oil in a "glass" container, under a nitrogen blanket, away from both fluorescent & sunlight and stored in the refrigerator.....that oil WILL NOT degrade very fast and will last a very very long time.

Dan
Semper Fi-cus

Thank you Dan. Great post.

That may explain also if you don't clean your Stainless steel BBQ grill right away, it gets very difficult to clean later.

Gasoline can also deteriorate after a while. So can machine oils.

dcarch

Being a retired petroleum fuels expert (i.e. qualified to give expert testimony in a court of law), I know about such chemical reactions and the chemical & physical properties of oil (hydrocarbons). The rules of petroleum organic chemistry apply equally well to everyday cooking. Understanding just a bit of chemistry can make one a better baker or a better cook.

Stainless steel is famous for acting as a catalyst for polymerizing the oil splatter from the healthier oils which are high in unsaturated fats. Lard and Crisco shortening (unhealthy oil) splatter on stainless will not get sticky or gummy.....because it was hydrogenated in the processing of those oils. Hydrogenation was done especially to remove those double bonded unsaturates that would go rancid. Hydrogenation makes an oil much more chemically stable and will last a long time without going rancid or getting gummy. That is why both Lard and Crisco shortening make very good coatings on cast iron pots and pans when one wants to keep those pans protected for long term storage.

Coat your cast iron pot/pans with regular cooking oil that has not be hydrotreated to remove those unsaturated fats and you will eventually get a sticky/gummy residue or build up that can be difficult to remove. It will also turn rancid given enough time. This can give foods cooked in that pan an off flavor.

Dan
Semper Fi-cus

Dan and dcarch - thanks so much for the information.

Teresa

Back to oil storage - how about those vacuum stoppers used for partly-consumed wine bottles, plus storing in the refrigerator?

Posted by johnliu "Back to oil storage - how about those vacuum stoppers used for partly-consumed wine bottles, plus storing in the refrigerator "

All perishable will last much longer in a refrigerator, even better in a freezer.

I am hesitant in the use of vacuum. I know that is a very established and common way of storing foods.

Especially using vacuum to store partly consumed wine.
It seems to me that alcohol has a lower boiling point, therefore, based on the vapor pressure theory, under partial vacuum, it will evaporate (distill) much faster than water. You may end up with wine that will have less and less alcohol contain.

The same goes for all foods. Any flavor essence, oils in food which have low boiling points may get evacuated under vacuum.

I have not seen any studies on this topic, therefore I am classifying this theory as my own superstition at this point.

dcarch

dcarch is right about vacuum distillation. It indeed will lower the boiling point of certain chemicals and can in effect remove some good compounds that add desirable flavors to food and drink.

However, it is IMPOSSIBLE for a vacuum stopper to remove any desirable compounds from cooking oil. The boiling point is still much too high at the vacuum level that those stoppers can attain. You would need to attain a vacuum level on the order less than one Torr to effectively boil cooking oil compounds at room (or refrigerator) temperatures. Too, those stoppers will still leak enough air (oxygen) over time to allow those high unsaturated fats (oils) to go bad. It is difficult to know when oxygen has leaked back into the bottle.

Bottom line.........nitrogen blanket would work much better.

Dan
Semper Fi-cus

So, Dan, grapeseed oil to season cast iron -- yes or no?

Because it contains a high percentage of unsaturated fats (oils), Grapeseed oil is one of The BEST oils you can use to season cast iron or high carbon steel (WOKs, crepe pans). The higher the percentage of unsaturates in the oil.....the more it wants to polymerize (the primary seasoning reaction). You can even season enameled cast iron skillets, pots, and pans(like Le Creuset) with it. You will even "season" your metal stovetop if you don't wipe away oil splatter ASAP!

Just don't leave any grapeseed oil coating on your pan for long term (months) storage purposes.....it will get sticky/gummy and eventually turn rancid. Use a light coating of Lard or Crisco for long term storage of cast iron....it won't ever go rancid or get gummy. Grapeseed oil is a great oil to use for seasoning pots and pans. You can find it often discounted at Marshall's or TJMaxx. Use the "high temperature" method that I've posted in other threads on the GW Cookware forum and I guarantee that you will be pleased with the results.

Dan
Semper Fi-cus

Thanks, Dan. I remember reading the long thread on seasoning cast iron, and the linked articles, and that there was disagreement about using high-smoke-point oils or low-smoke-point oils. There was a claim that oils with lower smoke points polymerized most easily and were therefore better.
Very high oven temperatures are a problem for me because I don't have a serious exhaust fan. I do have a couple of nice old frying pans that could use some re-seasoning.

"-----However, it is IMPOSSIBLE for a vacuum stopper to remove any desirable compounds from cooking oil. The boiling point is still much too high at the vacuum level that those stoppers can attain. You would need to attain a vacuum level on the order less than one Torr to effectively boil cooking oil compounds at room (or refrigerator) temperatures."

I do have a laboratory high-vacuum two-stage pump which I bought to try out a bunch of different things; Freeze drying, low temperature dehydrating, etc. Although I cannot boil oil with the pump, but it can easily boil water at room temperature. I will be trying to do a low temperature drying of concentrated stock to make ultra flavorful bouillons.

I need to buy new vacuum pump oil. It has been in the pump for a while.

dcarch

In 1984 we started up a H-Oil unit which was designed to hydro process a very heavy asphalt-like petroleum residual feed. This stuff was heavier than water and was solid at room temperature. In order to conduct a weight balance and conversion around this processing unit, we had to perform routine ASTM D1160 vacuum distillations. The vacuum pumps we used were two stage pumps and the oil had to be changed often so that they could maintain good vacuums for these distillations. Most two stage v-pumps have a valve that you can use to strip out most of the light hydrocarbon contaminats in the pump oil. This works but you eventually have to change out the oil to get a very good low pressure vacuum.

FYI....oils can be distilled up to a 1050 degrees F end point without it thermally cracking when using this type of distillation equipment. A few years after we started up this processing unit we began using High Temperature Simulated Distillation equipment which was much more reliable for following the conversion on that particular processing unit.

Your vacuum pump should work real well for concentrating stocks. Stock will boil at room temperature when under a good vacuum. And room temperature is not hot enough to break down any of the flavornoids that you worked so hard to get into that stock. I only see good benefits to stock reductions that are created under vacuum (low pressure) conditions.

Dan
Semper Fi-cus

Dan, I really should have a dehydration stage prior to the vacuum stage to avoid moisture contamination of the vacuum oil. I may do it with a serpentine tubing buried in dry ice.

The concept of making super flavorful bouillon cubes is interesting to me. As the water boils, it also gets freezing cold to further retard the evaporation of flavornoids, liquids. I think even after the broth freezes, scintillation can still occur.

BTW, This is a method discussed in the massive book ($500.00, 2,000 pages) just published "Modernist Cuisine". I am sure you will be very interested in that book with your scientific background. You may even be a consultant to the next edition of that book.

I may try to heat up some oils and see if I can boil them in my vacuum setup. I wonder what I can get out of highly flavorful oils such as olive oil, and sesame oil. But that would be a topic for distillation.

dcarch