Prudent Food Storage

The wise store up choice food and olive oil, but fools gulp theirs down. - Proverbs 21:20

Section 3 Specific Equipment Questions
A. Storage Containers



A.5 MYLAR BAGS

The word "Mylar" is a trademark of the DuPont corporation for a special type of polyester film. Typically made in thin sheets, it has a high tensile strength and is used in a wide variety of industrial settings.


In food storage, particularly for the long term, it is commonly found as a laminate with Mylar as the top layer, a very thin aluminum foil in the middle and one or more other types of plastic films on the bottom acting as sealant plies. This laminate combination possesses a high resistance to the passage of oxygen, carbon dioxide, nitrogen, other gasses, water vapor, and light which is what makes it valuable for our purposes. Unfortunately, it has a poor puncture resistance so must be used as an interior liner for more puncture resistant containers rather than as a stand-alone package.


Food grade aluminized Mylar complies with US FDA requirements and is safe to be in contact with all food types except alcoholic.


For food use, Mylar is most commonly available as pre-made bags of various sizes. Flat sheets or rolls of the material might also be found from which bags could be fashioned as well.


When Mylar bags are used by the storage food industry they are generally for products sealed in plastic buckets. The reason for doing this is the High Density PolyEthylene (HDPE) from which the pails are made is somewhat porous to gasses. This means that small molecules, such as oxygen (O2), can slowly pass through the plastic and come into contact with the food inside. The problem is further compounded if oxygen absorbers are used, as the result of their absorbing action is to lower the air pressure inside the container unless it has first been carefully flushed with an inert gas such as nitrogen. How fast this migration activity will occur is a function of the specific plastic formulation, its wall thickness and the air pressure inside the container. In order to gain the maximum possible shelf life a second gas barrier, the Mylar bag, is used inside the pail.


Whether the use of these bags is necessary for your home packaged storage foods depends on how oxygen sensitive the food item is and how long you want it to stay at its best. If the container is made of a gas impervious material such as metal or glass then a second gas barrier inside is not needed. If it is HDPE or a plastic with similar properties and you want to get the longest possible storage life (say 10+ yrs for grain) then Mylar is a good idea. If you're going to use the grain in four to five years or less then it is not needed. Provided the oxygen has been purged from the container in the first place, either with a proper flushing technique, or by absorption, there will not have been sufficient O2 infiltration to seriously impact the food. Particularly oxygen sensitive foods such as dry milk powders that are to be kept in plastic containers for more than two years would benefit from the use of Mylar. Naturally, storage temperature and moisture content is going to play a major role as well.


There is also the question of the seal integrity of the outer container. If you are using thin walled plastic buckets in conjunction with oxygen absorbers the resulting drop in air pressure inside the pail may cause the walls to buckle. If this should occur, there would be a risk of losing seal integrity, particularly if the buckets are stacked two or more deep. If the food was packed in Mylar bags with the absorbers inside this would keep the vacuum from seriously stressing the container walls. Better still would be not to have the problem at all by either using containers of sufficient wall thickness or flushing with inert gas before sealing. Heavy wall thickness is one reason why the six gallon Super Pails have become so widespread. It should be noted that Mylar is not strongly resistant to insect penetration and not resistant at all to rodents. If mice chew through your buckets, they'll go right through the bags.


A.5.1 HOW DO I USE MYLAR BAGS?

Sealing food in Mylar bags is a straight-forward affair, but it may take a bit of practice to get it right, so purchase one or two more bags than you think you'll need in case you don't immediately get the hang of it.


  1. The bags typically sold by storage food dealers look rather large when you compare them to the five or six gallons buckets they are commonly used in. That extra material is necessary though if you are to have enough bag material left over after filling to be able to work with. Unless you are sure of what you are doing, don't trim off any material until after the sealing operation is completed.

  2. Place the bag inside the outer container and fill with the food product. Resist filling it all the way to the top. You need at least an inch or so below the bucket rim left open to get the lid to seat completely. If you'll be using desiccants and oxygen absorbers together place the desiccant on the bottom of the bag before filling.

  3. When the pail seems to be full, gently thump it on the floor a few times to pack the product and reduce air pockets. Add any makeup food necessary to bring level back to where it should be.

  4. Take the bag by the corners and pull out any slack in the material so that all sides can be pulled together evenly. Place your oxygen absorbers inside if you are going to use them. Now place a board over the top of the bucket and fold the bag end down over it keeping it straight and even. Place a piece of thin cotton fabric such as sheet or t-shirt material over the edge of the bag mouth. Using a clothes iron set on the cotton, wool or high setting run it over the cloth-covered Mylar about a half-inch from the edge for about twenty seconds or so until it seals. You'll probably have to do the bag in sections. Temperature settings on irons vary so experimenting on a left-over strip to find the right setting is a good idea.

  5. When you've done the entire bag allow it to cool then try to pull the mouth of the bag open. If moderate pressure doesn't open it, fold the bag down into the pail until you feel the trapped air pillowing up against the material and wait to see if it deflates. If it stays buoyant, your seal is good. You can seal on the bucket lid at this point or take the further step to vacuum or gas flush the bag.

Once a seal has been obtained the bags can be left as-is, vacuum sealed or gas flushed. To obtain the most efficient oxygen removal the bags can be first drawn down with a vacuum pump and then purged using an inert gas.


Vacuum Sealing Mylar Bags


Once you have obtained a good seal on the bag, pulling a vacuum on the contents is straight forward.


First you'll need something to make a vacuum with. This can be either a regular vacuum pump, a vacuum sealer such as the Tilia Food Saver or even the suction end of your household vacuum cleaner. The end to be inserted into the bag will need to be of fairly small diameter in order to keep the hole in the Mylar from being any larger than necessary. This means that if you use a vacuum cleaner you'll need to fashion some form of reduction fitting. One such that I've seen is a plastic film canister with a hole drilled in the bottom and a piece of plastic tubing epoxied in place.


Cut a hole into the Mylar bag on a corner, making the opening only just large enough to admit the vacuum probe. Insert the nozzle and using a sponge, or something similar, push down on the material over the probe to make a seal. Now draw down a vacuum on the bag. When it's drawn down as much as possible, run a hot iron diagonally across the cut corner resealing the bag.


Gas Flushing Mylar Bags


Flushing with inert gas works essentially like vacuum sealing except that you're putting more gas into the bag rather than taking it out. You'll want to keep the entry hole small, but don't make a seal around it as above. Beyond that, follow the directions as given in Section III.B.2 - CO2 and Nitrogen. When you feel that the bag has been sufficiently flushed, run the iron across the corner as above to seal.


Flushing with dry ice can also be done, but it is important to wait until the frozen carbon dioxide has completely sublimated into gas before making the final seal otherwise the bag will burst like an overfilled balloon.




Updated: 9/18/96; 4/16/97; 7/21/97; 10/20/97; 9/15/98; 11/02/99; 12/01/03


Copyright © 1996, 1997, 1998, 1999, 2003. Alan T. Hagan. All rights reserved.


Excluding contributions attributed to specific individuals or organizations all material in this work is copyrighted to Alan T. Hagan with all rights reserved. This work may be copied and distributed for free as long as the entire text, mine and the contributor's names and this copyright notice remain intact, unless my prior express permission has been obtained. This FAQ may not be distributed for financial gain, included in commercial collections or compilations, or included as a part of the content of any web site without prior, express permission from the author.


DISCLAIMER: Safe and effective food storage requires attention to detail, proper equipment and ingredients. The author makes no warranties and assumes no responsibility for errors or omissions in this text, or damages resulting from the use or misuse of information contained herein. This FAQ is not intended for, nor should it be used in, any commercial food applications.


Placement of or access to this work on this or any other site does not necessarily mean the author espouses or adopts any political, philosophical or metaphysical concepts that may also be expressed wherever this work appears.



Table of Contents


Acknowledgements & Foreword


Section 1 - Shelf Lives


  1. Time, Temperature, Moisture, Oxygen and Light

Section 2 - Foods


  1. Common Storage Foods

A. Grains & legumes


  1. Grains & Grain Products
  2. Legumes
  3. Availability of Grains and Legumes
  4. Storing Grains and Legumes

B. Dairy Products


  1. Dry Milks
  2. Canned Fluid Milks and Creams
  3. Butter
  4. Cheese

C. Eggs


  1. Dry Eggs

D. Sugar, Honey and Other Sweeteners


  1. Granulated Sugars
  2. Honey
  3. Cane Syrups
  4. Corn Syrup
  5. Maple Syrup

E. Fats and Oils


  1. Buying & Storing Oils and Fats
  2. Extending Shelf Life By Adding Anti-Oxidants

F. Cooking Adjuncts


  1. Baking Powder
  2. Baking Soda
  3. Herbs & Spices
  4. Salt
  5. Vinegar
  6. Yeast

G. Infant Formula


  1. Alternatives to Breastfeeding
  2. Selecting and Feeding An Infant Formula
  3. Storing Infant Formulas and Baby Foods

H. MREs - Meals, Ready to Eat


  1. U.S. Military MREs
  2. U.S. Civilian MREs
  3. British/Canadian MREs
  4. Other Self-Heating Ready To Eat Type Products

I. Ration Bars


  1. Ration Bars

Section 3 - Specific Equipment Questions


A. Storage Containers


  1. What is Food Grade Packaging?
  2. Plastic Packaging
  3. Metal Cans
  4. Glass Jars
  5. Mylar Bags
  6. Reusing or Recycling Packaging

B. CO2 and Nitrogen


  1. Dry Ice
  2. Compressed Nitrogen

C. Vacuum Sealing


  1. Vacuum Sealing Considerations

D. Freeze Treating


  1. Freeze Treating

E. Oxygen Absorbers


  1. What Is an Oxygen Absorber?
  2. How Are Oxygen Absorbers Used?

F. Moisture in Packaging and Food Storage


  1. Why Moisture is Important
  2. What Is A Desiccant?
  3. Types of Desiccants
  4. How Do I Use Desiccants?
  5. Where Do I Find Desiccants?

G. Diatomaceous Earth


  1. What is Diatomaceous Earth?
  2. Where Do I Find DE and What Type Should I Buy?
  3. How Do I Use DE in Food Storage?

Section 4 - Spoilage


A. Insect Infestations


  1. Pests of Stored Grains, Legumes and Dry Foodstuffs
  2. Control of Insect Infestations

B. Molds in Foods


  1. Minimizing Molds
  2. Molds in Canned Goods
  3. Molds in Grains and Legumes

C. Bacterial Spoilage


  1. Botulism

D. Enzymatic Action in Food Spoilage


  1. Enzymatic Action

Section 5 - Shelf Lives


A. Food Product Dates


  1. "Best Used By", "Use By" and Other Food Product Dates

B. Closed Dating


  1. Closed Dating Codes Used by Some Food Manufacturers

C. Shelf Lives


  1. Shelf Lives of Some Common Storage Foods

Section 6 - Resources


A. Books


  1. Books

B. Pamphlets


  1. Pamphlets

C. Electronic-online


  1. Information sources
  2. Software sources

D. Organizations


  1. The Church of Jesus Christ of Latter Day Saints - LDS Family Cannery Guidelines

E. Food and Equipment Suppliers


  1. Mail Ordering Storage Foods What You Should Know
  2. Addresses of Suppliers

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