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StoringFatsOils

Page history last edited by amanda_christensen@usu.edu 11 years ago Saved with comment

Introduction

Edible fats and oils are not highly perishable food because of the absence of water.  Microorganisms require water to grow.  Fats and oils have variable shelf lives during which minor changes of their sensory characteristics occur.  Fats are generally solid at room temperature and oils are liquid at room temperature.  Fats and oils contain a glycerol backbone and 3 fatty acids that make up triglycerides.  The number of carbon units in the backbone determines its length.  The longer the fatty acid, the more likely the triglyceride is to be a fat; the shorter the fatty acid, the more likely the triglyceride is to be an oil.

 

Quality and Purchase

 Fats and oils are the raw materials for liquid oils (e.g. vegetable oil, olive oil), shortenings, margarines, and other specialty or tailored products that are functional ingredients in food products. They are commonly found in almost any grocery store usually in plastic containers of different sizes. The quality of edible fat depends on three factors: the type of raw material employed; the storage time and temperature of the raw material before rendering, and the type of rendering equipment used.  It is not recommended to home can butter for emergency storage.

 

 Rancidity is a chemical reaction of fats and oils that produces off-flavors and off-odors.  Fats and oils go rancid because of two chemical processes; hydrolytic rancidity and oxidative rancidity.  Hydrolytic rancidity occurs when the fat (triglyceride) is broken up into free fatty acids and glycerol by the presence of water.  The presence of the enzyme lipoprotein lipase (LPL) quickens this process. The unfavorable odor and flavor are the results of tasting individual short chain fatty acids instead of the whole triglyceride.  Dairy products are mostly affected by hydrolytic rancidity.[i]i Keeping fats and oils cold slows down the hydrolytic rancidity process, but even freezing does not stop the quality deterioration completely. (Nutrition and Dietetics 2007 8th edition. Margaret McWilliams)

 

Oxidative rancidity occurs in fats and oils that contain unsaturated fatty acids; mostly because unsaturated fats are less stable than saturated fats.  Oxidation produces an accumulation of aldehydes and ketones, which are compounds that are also responsible for the unfavorable flavors and odors.  Heat, light, oxygen, and metal ions encourage (speed up) oxidative rancidity. [ii] To prevent oxidative rancidity, products should be kept cool and covered or sealed from air.  Do not combine new and old fats.ii 

 

Packaging

Solid fats are often sold in cans or plastic versions looking like cans.  Oils are most often sold in plastic bottles.   Oils are rarely sold in glass containers anymore.  Metal cans are the most resistant to long term oxygen transfer (transmission of oxygen through the material over time).  Plastics are not that resistant to oxygen transfer and will allow significant oxygen levels into the container in 1-2 years. 

 

Storage Conditions

 All fat or oil foods experience deterioration even when handled and stored under ideal conditions. Store oils away from oxygen (air) as best possible.  Storing oils at a temperature below room temperature reduces the rate of oxidation and slows the development of rancid flavors.  Freezing oils or fats will not cause the container to explode out.  Fats and oils will actually contract a little when frozen.

 

Nutrition and Allergies

 Lipids (fats and oils) perform many life-supporting functions in each cell of our body. They are part of every cell membrane and every organ and tissue. Fats add a lot of the flavor to the foods that many of us are used to and savor and they also serve as a great energy source that provides 9 calories for every gram of fat consumed.  A few vitamins only dissolve in lipids. 

 

In a normal diet (non-emergency situation) there are healthier choices for fat intact.  Polyunsaturated and monounsaturated fats are less likely to cause heart disease compared to saturated fat.  Polyunsaturated and monounsaturated trans-fats also have health concerns.  However, during an emergency situation long term heart disease will take a back seat to immediate concerns for survival.

 

There are no known allergies associated with fats or oils.  Some may think that soybean oil would be an allergy, however commercially processed soybean vegetable oil contains no protein and therefore it is not allergenic.

 

 

Shelf Life [vi],[vii],[viii]

All fat or oil products experience deterioration even when handled and stored under ideal conditions. Oils that do not require heating to remain liquid resist deterioration more than the higher melting products. Most shortening and other similar products will maintain an acceptable flavor and oxidative stability for two or three weeks in melted form with adequate controls.

Type of Fat/Oil

Refrigerator

Freezer

Pantry

Butter, opened

2-3 weeks

--

--

Butter, unopened

1-2 months

9 months

--

Vegetable oil, opened

--

--

1-3 months

Vegetable oil, unopened

--

--

6 months

Salad oil, opened

--

--

2 months

Salad oil, unopened

--

--

3 months

Margarine, opened

1 month

--

--

Margarine, unopened

4-5 months

1 year

--

Peanut butter, opened

6 months

--

2-3 months

Peanut butter, unopened

--

--

6-9 months

Vegetable shortening

6-9 months

--

3 months

Olive oil*

--

--

1-2 weeks

*Olive oil can become rancid quickly at room temperature, but it develops fat crystals in the refrigerator.  However, olive oil can be stored in the refrigerator and allowed to thaw.[ix]

 

Use from Storage

Fats and oils can be used as is directly from storage.  Once a container is opened and contacts air the shelf life will drop.  Therefore, opened containers should be used relatively quickly.  Rancid fats or oils cannot be made palatable.  Few recipes could possibly add enough strong ingredients to distract the human palate.  Simply discard rancid oils and replace them.

 

References:

 


[i] fshn.ifas.ufl.edu/faculty/mrmarshall//fos4311/labs/Laboratory%208.doc

[ii] http://www.cfs.purdue.edu/class/f&n202/pdf_full/Fats_and_oils.pdf

[iii] Kilcast D, Subramaniam P. (2000). The Stability and shelf life of food. Cambridge, England: Woodhead Publishing Limited; 2000

[iv] McWilliams M. (2007). Nutrition and Dietetics 8th edition. Pearson Education Inc; 2006

[v] http://www.mayoclinic.com/health/fat/NU00262

[vi] Boyer R, McKinney J. "Food Storage Guidelines for Consumers." Virginia Cooperative Extension (2009): n. pag. Web. 7 Dec 2009

[vii] Assistant Professor Franco Milani, Department of Food Science, University of Wisconsin Land O’ Lakes consumer help line: 1-800-328-4155

[viii] Cupboard Storage Chart." K-State Research and Extension n. pag. Web. 23 Dec 2009. <http://www.ksre.ksu.edu/humannutrition/hrap/storage/cupstor.htm>.

[ix] McWilliams M. (2007). Nutrition and Dietetics 8th edition. Pearson Education Inc; 2006

[x] http://www.cfs.purdue.edu/class/f&n202/pdf_full/Fats_and_oils.pdf

  • Kilcast D and Subramaniam P. 2000. The Stability and Shelf-Life of Foods. Boca Raton, FL: Woodhead Publishing and CRC Press, LLC. P 279, 303.
  • O’Brien R. Fats and Oils. 2004. Boca Raton, FL: CRC Press, LLC. P 1, 144
  • Hui Y. 2006. Handbook of Food Science , Technology, and Engineering. Volume 4. Boca Raton, FL: Boca Raton, FL: CRC Press, LLC. P 155.
  • Haas E and Levin B. 2006. Staying Healthy With Nutrition. Berkley, CA: Celestial Arts. P 74
  • Erickson D. 1990. Edible Fats and Oils Processing: Basic Principles and Modern Practices. The American Oil Chemists Society. P 31.

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