Hope that got your attention. Actually I'm referring to using paraffin to seal your jams and jellies. It's been done forever, I know, and you may be thinking, "It was good enough for grandma, it's good enough for me." And you may very well be right. However, the Practical Preserver is all about safety, so hear me out and then make up your own mind. I promise not to sulk.
Back in the day, jams and jellies and other fruit spreads were generally stored in very cool conditions - an unheated back porch, the basement (or cellar if you grew up back East), or in some other dark, cool place. Today, homes are heated to the max. We've got coils embedded in our cement garage floors to keep our cars nice and toasty warm throughout the winter. Not too many of us even have a back porch, and if we do, it's probably not designed with food storage in mind. You most likely will be storing your preserves in the pantry right off the kitchen. Warm. Comfy. But not if you're a preserve. And especially if you're a preserve sealed with paraffin.
So much for the background. Molds and fungi grow beautifully in warm conditions. Once these spoilers get growing, they can penetrate all the way down to the bottom of the jar. Yes, I know that folks used to just scoop and scrape off the mold and use the preserve, but it's an iffy idea. You're preserving food to nurture your family, so feeding them mold or fungus isn't a spiffy idea.
One final convincer: Making preserves is a fun family activity, but heating paraffin so you can pour it on top of the jam or jelly is literally playing with fire. It can give you a nasty burn and can also catch on fire in the blink of an eye.
So, there you have it. Best practice is to use lids and rings and ensure a tight, safe seal.