There used to be just a couple of books about how to can and preserve food on the market, but the last few years have just seen an explosion of new ones. On the one hand, this is great – as an avid cookbook collector and active canner, I just love flipping through new books and finding new things to try. On the other hand, this can be troublesome. Canning isn’t exactly like cooking – food safety is critical, so you’ve got to have an understanding of the basic science of why some methods work and others don’t. And unfortunately, there are some books floating around that are rife with misinformation.
So how to tell the good ones from the bad ones? First off, you want to educate yourself on the current guidelines for food preservation as laid out by the USDA-affiliated National Center for Home Food Preservation as well as Ball – probably the two most reliable resources out there. They both research and test recipes under strict conditions and their recommendations are as good as gold. Once you understand the basics of what you should and shouldn’t do, it’ll be fairly easy to determine if a book is going to produce goods that are safe to consume.
The basic no-no’s in canning are pretty simple and straightforward –
– You cannot process dairy products (milk, cheese, cream, butter, etc.). Dairy is a low-acid product and it can go rancid when stored at room temperature, increasing the likelihood of nasties like botulism and e coli.
– You should not use dry heat (like an oven) to “can” anything – only moist heat in the form of a water bath canner or pressure canner should be used. Jars are much more prone to crack or even explode in the oven.
– You cannot “can” baked goods. First off, baked goods are likely low acid, which can open the door to rapid spoilage. Secondly, they’re so dense that it would be difficult for heat to fully penetrate the product, killing any nasties. And you should never use jars in a dry heat environment anyway, as mentioned above.
– You cannot use a larger jar size than what is specified in the recipe. Canning recipes have been tested for adequate processing time for the density of the food product in a given size of jar – if you were to increase the jar size for a recipe you would have no way of knowing if the heat got all the way to the center for long enough in order to sterilize the contents.
– “Open kettle” canning is not a safe method for food preservation. This antiquated process is simply the practice of putting hot foods into hot canning jars and flipping them over, so the warmth of the food in the jar creates a mild vacuum seal. Since the seal is weaker than what would be achieved with water bath or pressure canning and the contents have not been processed at high enough temperature, spoilage can occur.
When you pick up a new canning book, don’t just skip straight to the recipes. Read through the introductory chapter(s) first to see what kinds of practices the author advocates. If they’re in line with the USDA/Ball guidelines then you’re in good company and you should feel confident with the recipes. If they’re not in line – put the book down. I recently flipped through a new canning book that was downright scary in it’s recommendations – despite what the author thinks, “why not” is not a good reason to mess around with food safety. Beware of the books that try to tell you that violating the above best practices are no big deal. You can’t taste, smell, or see botulism – better to know that you’re following established guidelines so you’ve got no doubt in your mind about the safety of your home canned goods.