Canning

Can I can bread or cake in a jar?

These products are not recommended for canning; choose recipes that you can freeze. In fact, most of these products are not really "canned." The directions call for baking in the jar and then closing with a canning lid. Many recipes for quick breads and cakes are low-acid and have the potential for supporting the growth of a bacteria like Clostridium botulinum if it is present inside the closed jar. One university's research showed a high potential for problems. You will see these products made commercially; however, additives, preservatives and processing controls not available for home recipes are used. Canning jar manufacturers also don't endorse baking in their canning jars.

How do I can oil with herbs? Can I can pesto?

Herbs and oils are both low-acid and together could support the growth of the disease-causing Clostridium botulinum bacteria. Oils may be flavored with herbs if they are made up for fresh use, stored in the refrigerator and used within 2 to 3 days. There are no canning recommendations. Fresh herbs must be washed well and dried completely before storing in the oil. The very best sanitation and personal hygiene practices must be used. Pesto is an uncooked seasoning mixture of herbs, usually including fresh basil, and some oil. It may be frozen for long term storage; there are no home canning recommendations.

Is it safe to jar already canned food?

Often people think that they can save money by buying larger containers of canned food, transferring the contents (or leftovers from the first use) to smaller jars and re-processing it. Others wonder if this is a way to save leftovers from any size can for a longer time than they will keep in the refrigerator.

There are several problems with these practices:
(1) We have no safe tested processes to do this. In some cases, the way the heat is distributed throughout the jar during canning will be very different if you start with already canned/cooked food than with fresh. Excessively softened foods will pack more tightly into a jar, or arrange themselves differently and the process time recommended for fresh foods will not be enough for the already canned foods. Underprocessing can lead to foodborne illness or at the very least, spoilage and loss of product. You definitely could not just transfer the food and "seal" the jar. You would need some heat treatment known to destroy any organisms transferred with the food.

(2) The expense and time of recanning foods far exceed the cost savings of bulk or large-quantity packaged foods. To re-can food, you now add the expense of a jar and lid as well as the energy to re-can the food.

(3) Most likely the quality of the food will be greatly reduced in canning the food for a second time. The heat of canning does cause loss of some nutrients, and a second round of canning will further reduce the nutritional value. Textural changes from heating will be added to those already produced.

Without tested processes for re-canning foods, there is no way to know how to reduce the canning process and the default (although not a recommendation) is to process for the full time and temperature as if starting from scratch. When you consider you are not even saving money and resources, it does not seem worth the loss of food quality to practice this re-canning of commercially canned food. Our recommendation is to not plan to do this.

Should I use directions for canning butter at home that I see on the Internet?

Indeed, there are some directions for 'canning' butter in circulation on the Internet. Most of what we have seen are not really canning, as they do not have Boiling Water or Pressure Canning processes applied to the filled jar. Jars are preheated, the butter is melted down and poured into the jars, and the lids are put on the jars. Some directions say to put the jars in the refrigerator as they re-harden, but to keep shaking them at regular intervals to keep the separating butter better mixed as it hardens. This is merely storing butter in canning jars, not ‘canning’. True home canning is when the food is heated enough to destroy or sufficiently acid enough to prevent growth of all spores of Clostridium botulinum (that causes botulism) and other pathogens during room temperature storage on the shelf.

Additionally, when you consider the economics of the process (energy costs involved with heating, cost of jars and lids, etc.), even if the butter is bought on sale, it may not be economically viable to prepare butter to store for years in this manner. Good quality butter is readily available at all times, if butter is needed for fresh use. If the concern is about emergency food supplies, there are dry forms of butter that can be purchased and stored, oils that can be used in an emergency, or commercially canned butter in tins (although we have only seen this for sale from other countries). Melted and re-hardened butter may not function the same as original butter in many types of baking anyway.

There are a few issues with the common directions circulating on the Internet at this time (Spring 2006):

1. Physical safety and food quality: In the provided directions, the jars are preheated in an oven (dry-heat), which is not recommended for canning jars. Manufacturers of canning jars do not recommend baking or oven canning in the jars. It is very risky with regard to causing jar breakage. There is no guarantee that the jars heated in this dry manner are sufficiently heated to sterilize them, as we do not have data on sterilizing jar surfaces by this dry-heating method.
2. The butter is not really being 'canned'; it is simply being melted and put in canning jars, and covered with lids. Due to some heat present from the hot melted butters and preheated jars, some degree of vacuum is pulled on the lids to develop a seal. It rarely is as strong a vacuum as you obtain in jars sealed through heat processing. The practice in these 'canned' butter directions is referred to as 'open-kettle' canning in our terminology, which is really no canning at all, since the jar (with product in it) is not being heat processed before storage.
3. Although mostly fat, butter is a low-acid food. Meat, vegetables, butter, cream, etc. are low-acid products that will support the outgrowth of C. botulinum and toxin formation in a sealed jar at room temperature. Low-acid products have to be pressure-canned by tested processes to be kept in a sealed jar at room temperature. It is not clear what the botulism risk is from such a high-fat product, but to store a low-acid moist food in a sealed jar at room temperature requires processing to destroy spores. A normal salted butter has about 16-17% water, some salt, protein, vitamins and minerals. Some butter-like spreads have varying amounts of water in them. We have no kind of database in the home canning/food processing arena to know what the microbiological concerns would be in a butter stored at room temperature in a sealed jar. In the absence of that, given that it is low-acid and that fats can protect spores from heat if they are in the product during a canning process, we cannot recommend storing butter produced by these methods under vacuum sealed conditions at room temperature.
4. Some other directions do call for 'canning' the filled jars of butter in a dry oven. This also is not 'canning'. There is not sufficient, research-based documentation to support that 'canning' any food in a dry oven as described on this web page or any page that proposes oven canning is even sufficient heating to destroy bacteria of concern, let alone enough to produce a proper seal with today's home canning lids.
   
   In conclusion, with no testing having been conducted to validate these methods, we would NOT recommend or endorse them as a safe home-canning process, let alone for storing butter at room temperature for an extended period. We do know that the methods given for preheating empty jars, or even filled jars, in a dry oven are not recommended by the jar manufacturers or by us for any food. Aside from the physical safety and quality issues, and the fact that it is not canning at all, if there happened to be spores of certain bacteria in there, these procedures will not destroy those spores for safe room temperature storage.

Can I can shelled nutmeats?

We no longer recommend canning a dry pack of shelled nutmeats at home. The previous canning process from the University of Georgia was a way to create a vacuum-sealed jar , but  there is no documentation for any microbial sterilization that might have been taking place. More recent research has shown that some species of Salmonella are tolerant of drier (low water activity) conditions, and based on this information, canning nutmeats in a dry pack could be potentially hazardous using the directions we previously had if any condensation or moisture pockets formed inside the jar.  There is not a substitute canning process for preserving dry packs of nutmeats at this time. There are other options for vacuum sealing of dry meats for either room or freezer storage, using small appliances which pull air out of packages before sealing.