The moisture content of the grain or legume you want to put by has a major impact on how long you will be able to keep it in storage and still remain nutritious and edible. Some of the available literature states that grain with a moisture content as high as 13% can be safely put up, but there is a risk to keeping it at that level that should be understood.
The outside of every kernel of grain and bean you buy or grow hosts thousands of fungi spores and bacteria. This is all perfectly natural and is not a reason for alarm. The problem lies in that at moisture levels between 13.5% to 15% some fungal species are able to grow and reproduce. Aerobic bacteria (needing free oxygen to survive) require moisture in the 20% range. If you have grain with a moisture content as high as 13% you are perilously close to having enough moisture to enable mold growth which could lead to the spoilage and loss of your product. For this reason, I suggest you keep all grains and legumes to a moisture content of no more than 10%. An exception to this is raw peanuts which are particularly susceptible to an Aspergillus mold growth that produces aflatoxin (a type of mycotoxin) and should be stored with an 8% moisture content or less.
If you do not have a clue as to what the moisture level of your grain is here are several methods to determine it. The first method is quick, simple and will usually give you a close enough idea to work with of how much moisture there is in your grain or legume. The last two require a great deal more time and effort, but give much more precise results.
The quick and dirty method requires nothing more than crushing a kernel of grain or bean between two solid objects like a hammer and a brick. You don't have to hit it like you're driving spikes, just give it a sharp rap. If the grain shatters nicely into powdery debris or many small bits then the moisture level ought to be in about the right range and you can package as-is. If the kernel only mashes flat or only reluctantly breaks into pieces it probably has too much moisture. If you're not sure of what you're seeing try drying a small amount overnight at only a warm temperature (100º Fahrenheit) such as you'd get from the pilot light in a gas oven. The next day take another sample from the same container and rinse in warm water for a few seconds, wipe dry on a towel and let sit for about ten minutes. Now try the crush test on both samples. One should give you a good result and the other should be much different. Any seed with a high fat content such as soybeans and peanuts will not work well with this method.
THE OTHER METHODS
The more highly precise moisture content measurements require more time and equipment. It is possible though to make determinations with just home equipment that will be of real use for our purposes.
You'll need some way to measure weight with a fair degree of accuracy. The better the scale you use, the more reliability you'll have in your determinations. Provided that it will weigh accurately to the half-ounce or less, any scale that can be calibrated with a known check weight will do. Even postal scales can be made to serve if they are carefully calibrated against a known weight. Many individuals interested in starting storage programs may have grain weight scales used in ammunition reloading that might serve well.
Also necessary is a thermometer capable of withstanding and accurately measuring oven temperatures. As many bakers can tell you, home oven thermostats are often notoriously inaccurate so it is better to rely on a decent thermometer. Most kitchen supply stores can supply one that is oven safe and will accurately measure to the degree Fahrenheit or Celsius.
Proper technique calls for preheating the oven for a half- hour or more before starting the dehydrating process so that it will be of a uniform heat throughout. The sample pan should be placed on the middle rack as close to the vertical and horizontal center of the oven as possible. The bulb or dial of the thermometer should be placed next to the pan.
This method is for measuring moisture content in whole grains and legumes. Grain flours or meals, milk powders and any other finely textured foods should use method two detailed below.
To be done prior to measuring -- choose a shallow heat resistant container that has a close fitting lid. Clean it thoroughly and dry it completely in your oven for 10-15 minutes. Allow it to cool and then weigh it carefully. This will give you the tare weight or what your container weighs empty.
Depending on how your scale is calibrated you can use a smaller sample size than what is indicated below. Using the twenty-ounce sample mentioned in the following text will allow for fairly accurate readings with the average postal scale. A scale that will measure to the gram could use as small a sample as 20 grams. A powder scale could use even less, but the smaller your sample size becomes the more finicky care you must take not to allow error to creep in. Keep your sample size large enough to easily work with.
Allowing for the weight of the sample pan, measure out a weighed twenty-ounce representative sample of the grain or legumes in question. Ideally, you should mix the entire lot thoroughly immediately before removing the sample, but if this is not possible then take it from the middle center of the container. It is important that you use care in this measurement since it will affect all following determinations.
Put the sample in the container making sure it is not more than an inch deep. Place it in the oven with the lid off and allow to heat. Below is a table giving the oven temperatures and times per grain or legume type:
------------------------------------------------------ Oven Temperature Oven Time Seed Deg. F C Hours Barley 266 130 20 Beans 217 103 72 Corn 217 103 72 Oats 266 130 22 Rye 266 130 16 Sorghum, millet 266 130 18 Soybeans, peanuts 217 103 72 Wheat, rice 266 130 19
When the dehydration period is over place the close fitting lid on the sample pan and allow to cool in the oven with the door closed. Remove the pan and carefully weigh it.
A one ounce loss in weight indicates your grain has a roughly five percent moisture content, 2 ounces indicates that it has a 10% moisture content, etc., etc. You might even be able to cut it as fine as a half-ounce loss, but I wouldn't try to take it further than that.
Obviously, this is only a rough measure, but it works and can be done with postal or dietetic scales that are available virtually everywhere. As I mentioned above, if you have a scale with a finer calibration it is possible to use a smaller sample size and achieve the same result.
This method is much faster to use than the first, but greater care must be taken to prevent error. It can be used to determine moisture contents of whole grains and legumes, flours, meals and various food powders.
The same equipment as was used in Method Two will be required here as well as a low-RPM grain mill or some other device that can reduce a quantity of the grain to a meal consistency with only minimal heating of the sample. If the food to be tested is already at a meal consistency or finer then it can be used as-is.
Grind a quantity of product from which you want to measure the moisture content. Take care to grind the sample slowly enough to keep friction heat build up to a minimum (should not be more than mildly warm) or else moisture will be lost due to heat evaporation before it can be weighed.
Immediately upon finishing the grinding, weigh out your sample so as to minimize unmeasured moisture loss.
Place the sample in the oven and dehydrate in the manner used in Method One for a period of two hours at a temperature setting of 275º F (135º C). When the heating period is finished cover with the tight-fitting lid and allow to cool in the oven. Remove and weigh carefully. Moisture determination is the same as above.
If anyone has a better way of measuring moisture levels which can be done without a lab or special equipment I'd surely like to hear it.
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Copyright © 1996, 1997, 1998, 1999. Alan T. Hagan. All rights reserved.
Excluding contributions attributed to specific individuals all material in this work is copyrighted to Alan T. Hagan and all rights are reserved. This work may be copied and distributed freely as long as the entire text, my 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.
Revised: 1 Dec 99