My Journey Through Historical Culinary Science

Yesterday I did not know the melting point of food-grade paraffin wax. Today I can tell you that paraffin is a mixture of solid straight-chain hydrocarbons with a range of melting points from 120° to 150° F.   And just as there is a range in melting points, there is also a range in the specific gravity. Specific gravity for paraffin wax varies from 0.82 to 0.96. The variations arise from the degree of refining - the less refined, the higher the oil content, the lighter the wax, the lower the specific gravity.  This will become important later. 

"Melting points and specific gravities?" you ask.  The issue arose because there's been shortage of canning lids for the past two years. That's been common knowledge in some circles—the Preppers in online Zombie Apocalypse chat rooms have been trading notes on the phenomena for months. But the shortage got personal for me a little over a week ago when the muscadine vines were beginning to ripen and the hunt for jelly lids was on!

That's is when I remembered that my mom made grape jelly every September and sealed the jars with Gulf brand paraffin. Food-grade paraffin seals are a good, economical alternative for preserving jams and jellies that will be eaten within a year.  I recall the process pretty well, and I also have cook books dating to that era which I reviewed before writing this piece. Then I checked that knowledge against what shows up in DuckDuckGo searches in 2021. Oh, my goodness!

WARNING!  TIME TRAVELING IS INVOLVED! 

Some of the "modern science" search results warned against using paraffin claiming that the seals were unreliable, allowed mold to develop, and had short shelf-life.  But I believe that I figured out what they were doing wrong. They are ignoring the old physics of melting points and specific gravity when it came to reliability and mold growth, and as to the storage life, if the intent is to store your jelly until the next canning season comes around when you can make more, no problem, you'll be fine.  

The sites that did give instructions for sealing with paraffin were pretty insistent on using a candy thermometer to keep the wax from catching fire.  They warned to not let the melting wax get any hotter than 375ºF. That seemed crazy to me. Not the fire warning part, but the implication that 374º might be safe. 

And that is where my mental time traveling began. We never used a candy thermometer. We kept an eye on the pot. When one seals jelly like this every year, you develop a sense for melting the wax.  (Smoking wax is bad!) The paraffin will turn clear and be fully melted at much lower temperatures. Use a double boiler set-up that will help keep it below 250ºF. 

The main difference I found between today's instructions and the way my ancestors made paraffin seals was that, after pouring the hot jelly into sterilized jars, they let the jelly cool enough to begin to set up before either pouring or spooning on the melted paraffin.   

>> Jelly does not have to begin to set up solid before sealing it with paraffin! <<  

Waiting for it to begin to set only gives the jelly more time to be exposed to the air and become contaminated at lower temperature before sealing, and cooling first increases the possibility of an air bubble under the seal. The only real reason for waiting would be if you were unsure if the pectin level was high enough to cause the jelly to set at all.  And that's a whole 'nuther issue.

So this is where the science of specific gravity comes in.  Pure water with no dissolved salts has a specific gravity of 1. A specific gravity of less than one means the substance is lighter than water and will float on it; a specific gravity greater than one means the substance is heavier than the water and will sink. Jelly is heavy. Paraffin will float on jelly. (Also why, if the aforementioned smoking wax does catch fire, water won't help douse the flames; it floats them over to ignite the next flammable object.)

Here are the facts: Melted food grade paraffin does not mix with hot liquid jelly. You can pour melted paraffin into the jars of hot jelly and it will float to the top, making an air tight seal as it cools and solidifies.  Pour in enough paraffin to raise the surface level about one-third inch. That gives a comfortable margin for error when eyeballing the thickness. You want a quarter-inch minimum, but not so thick that the seal is hard to break when it's time to eat the jelly. 

Won't trace amounts of paraffin be trapped in the jelly? Probably, if you are measuring down to ppm. But if you are worried about that, you will also have to give up chocolate chip cookies and chocolate candy bars for life, because glossy chocolates and chocolate chunks that resist melting in your hand probably have paraffin added, and so do cosmetics and lip glosses.  Are you ready to give up your ChapStick® too?  

Do you need to add lids on top of the  paraffin seal?  It depends...   The jelly needs to be stored in a dark and reasonably cool place, below 90º at which point the paraffin may start to soften. Adding a metal or plastic lid adds another layer of safety in a couple areas. A lid eliminates problems of dust getting into the jelly when the seal is broken, because it is easier to wipe off a lid than it is to dust off wax. Lids would be important if the jelly is kept in a root cellar that critters might break into. Having a lid is useful after the jar is opened because the paraffin gets thrown away or otherwise recycled, but it is not reusable as a top for the remaining jelly. 

That's the practical part of the story, but it misses the fond memories part.  The fond memories part includes my mid-summer discovery of hard green balls growing on the vine and anticipating their ripening into grapes. It includes the heavy-duty scissors (where I'd watched the salesman cut a penny in two to prove their strength) that were used to harvest the grapes.  It included memories of the kitchen window that did not open, but had a 3½" high screened vent at the bottom (and a panel that would cover it in the winter), and how precious the feeble airflow was when boiling down the grapes on a hot stove. I remember straining the juice using an old cloth diaper that was rigged to hang from a cabinet handle and catch the dripping juice in a stoneware crock. Those kitchen cupboard handles would have looked equally at home on a 1950 Cadillac, but they were durable! I recall being amazed watching the paraffin float to the surface of the hot jelly. And One More Thing—  it was a very special privilege to be chosen to break the seal on the jelly!   It is so much cooler than unscrewing a jar.