Canning

Safety Precautions

Canning is a time honored, proven way of preserving a harvest or hunt for a very long time. In the course of a day one can “put up” enough tomatoes (or other item) to last until the next year’s harvest. However, to prevent illness or injury during the process, all instructions must be followed completely. There are no shortcuts when preserving food, no matter which method is used.

Let’s start with a brief description of how and why canning preserves food. To preserve food, microbial growth and enzymatic changes must be halted or eliminated altogether. In canning, food is brought to a boil for a specified period of time to sterilize it.

It is then packed into sterile jars, and sealed with sterile lids. Stopping here would keep the food edible for only a short period of time. You might be asking how, if everything has been properly sterilized, any microbe would exist to spoil what you have so carefully prepared. What is in the jars? Your carefully prepared food is there, yes; but also there is air – non-sterile air, to be exact. How do we get rid of the air?

If the food is acid enough, it can be processed in an open water bath. Boiling does not kill the spores of the botulism bacteria (Ciostridium botuiinum); however, the high acid prevents these spores from growing.  The hot, sealed jars are set on a rack and placed in a kettle of boiling water for a set period of time.

The water must be kept at a brisk boil the entire processing time. Should the water fall below the boiling point, it must be brought back up to boiling and the processing time started over. Also the level of the boiling water must be kept at least an inch deeper than the height of the jars (do not mix jar sizes in the batch).

This process is sufficient for driving the air out of the jars. After the processing time is complete, the jars are removed from the water, the rings or lids tightened as needed, and set on wire racks to cool. Almost immediately you will hear that satisfying “pop” of the lids concaving, showing that a vacuum has indeed been created in the jars. After the jars have cooled, test each one by pressing on the center of the lid. If it flexes when you push down, it is not sealed. Any jar not vacuum sealed must be reprocessed or refrigerated and eaten within a few days.

Pressure canning is necessary for foods that do not contain a high enough acid to prohibit the growth of botulism spores. While the temperature of boiling water (212oF) is not high enough to kill this bacteria’s spores, pressure canners can increase the temperature to 240oF, holding it there long enough to kill them completely.

 

Whether your recipe calls for the food to be hot or cold, it must be packed loosely, and boiling water poured into the jar to eliminate air pockets. Jars are never filled to the brim.

Food swells during processing. If it oozes out of the jar, it can prevent the lid from sealing securely to the jar. If the jar is not packed with enough food and water, too much air filled space is left and the air is not completely exhausted during the processing time. Either event will allow spoilage to occur. This space is called “headspace”. The amount needed is specified in each recipe and needs to be adhered to. Use a ruler to ensure you have it correctly.

Work surfaces, tools, utensils, and equipment must all be clean (and in some cases they must be sterile) and in good condition. If pressure canning, the lid’s gasket (rubber seal) and rubber safety valve cover must be of the correct size (check for stretching or shrinking), have no cracks, and must be inserted into the lid and seated correctly. Follow the instructions provided by the manufacturer.

Pressure canners are sturdy vessels made of cast aluminum or stainless steel. They can last multiple lifetimes if properly cared for. If you received your pressure canner without instructions, as can happen with hand-me-downs, you can usually find them on line. Begin this search by looking for a website for the manufacturer. It might take a little digging to find, but most are there. If not, there are websites devoted to only instruction and owner’s manuals available in PDF formats, usually for no cost.

Should you need to replace the gasket, these are readily available in most places that sell the cooker. If you have difficulty finding the one you need, they can be ordered on line. These items are inexpensive, at the time of this writing they are generally around $10 (US).

They are frequently sold in a kit that includes the rubber stopper for the safety valve. This is because if the safety valve has been blown, both it and the gasket need to be replaced before using the canner again. Also, find out the reason it blew out and avoid making that mistake again. After interviewing several canners, and in my own experience as well, I have never heard tell of a “blow out”. But I was always reminded to follow instructions carefully.

Jars must be manufactured for the canning process. These jars are properly tempered for the extremes in temperature and pressure they will be placed under. Never use old peanut butter or commercial jelly jars. Your jars should be free of cracks and chips. If using rings and lids, the rings should be round and screw onto the jars easily. Lids, with a rubber-like seal embossed onto it, are meant to be used only once.

Never reuse last year’s lids. Lids should not be dented. Remember, you are trying to produce not only an air-tight, water-tight seal, but also a vacuum in the jar. The seal must be sturdy enough to maintain this vacuum. If using jars with rubber rings and bails clamping the lid into place, these too must be in good condition. The ring must have no cracks and must be of the correct size, covering the entire rim of the jar.

Separate lids and seals nearly disappeared from the marketplace; however they are now making a comeback. If using these, careful inspection should be made of each item to be sure it is in serviceable condition. Also coming back are screw-on lids that require no separate ring. But like the flat lids, they are embossed with a seal. While very handy to use at the time, they are not reusable.

Recipes are also to be followed carefully. Although some seasonings can be adjusted to taste, salt, sugar, vinegar, or alcohol should be measured accurately. These are the anti-microbial elements that ensure your end product is safe for consumption.

Altitude Adjustments

It is always possible to find a regional cookbook that has already figured in altitude adjustments, but this is highly unusual. Every book I have seen assumes you are at or near sea level. Why is this important? Because altitude affects the temperature at which water boils. If you live below 1,000 feet above sea level, you have no corrections to make to the process.

If you live between 1,000 and 2,000 feet above sea level, you need to begin making adjustments. There is no need to adjust pressure canning yet; but if water bath canning an adjustment is needed. When above 2,000 feet adjustments need to be made in pressure canning. Use the table below if you live above 1,000 feet. If you live above 10,000 feet, consult with your local extension office.

Pressure canning requires no change in processing time but does require changes in the amount of pressure held so that the temperature inside the canner reaches 240oF. This temperature is what kills the botulism bacteria. More information about this can be found in the Pressure Canning Details.