It's important to know that not all foods are suitable or safe for canning in a water bath canner or even a pressure canner. Chia-based jams are a good example.
Used in lieu of pectin, chia acts as a natural thickener. Because, unlike most commercial pectins, it doesn’t require sugar to set, it’s an effective way to make low-sugar jams that still have a thicker texture. (It could be argued that these are not in fact jams, but more akin to puddings.)
However, I’ve seen examples of recipes in blog posts that call for chia and include water bath canning instructions. This is not advisable, for a few reasons. Here’s what you need to know.
Why You Shouldn't Use Chia in Canning Recipes
There are three major factors when it comes to recipes being safe for water bath canning. The first is acidity. Foods with a pH of 4.6 or lower, which is to say higher in acid, prevent the growth of c. botulinum, which in turn can produce the deadly botulism toxin. Most fruits are naturally high in acid, which is why they are safe to can on their own and in jam. However, chia is a low-acid ingredient, and so by adding it you are raising the pH level, potentially creating unsafe conditions.
The second factor is water activity (aw), which is defined on a scale of 0 (bone dry) to 1 (pure water). The good news is that c. botulinum generally cannot exist in an aw lower than 0.93.
However, other pathogens such as staphylococcus aureus can exist in environments with an aw of 0.86.
The third is viscosity, or density. As the viscosity increases, the jam becomes denser, and it is harder for temperatures in the jar to consistently reach the level of lethality for those bacteria during the water bath canning process.
More liquid jams, by contrast, heat more evenly. This is also why it is unsafe to can low-acid purees and butters like pumpkin butter.
Chia is an imprecise additive. When you add it, the water in the fruit gelatinizes the seed, which absorbs water, increasing viscosity; the acidity level is also lowered. But there is insufficient information on exactly how dense the jam becomes, what the water activity is, and what the acidity level comes to. Consequently, it is not safe to can jams made with chia in the home, by any method.
It’s worth noting that the same is true for nearly all starches. Grains and flours should not be added to jams, pie fillings or other foods prior to canning. The sole exception to this is Clear Jel, a corn starch derivative, commonly used for canned pie fillings. The National Center for Home Food Preservation (NCHFP) endorses the use of Clear Jel in tested recipes.
Another way to create a set for low-sugar jams is to use Pomona’s Pectin, an alternative type of pectin powder that reacts with calcium water solution to thicken in the way that standard pectin does, yet does not require sugar to create the set.
Thanks to Master Food Preserver Ernest Miller of Rancho La Merced Provisions for assistance on this story.