What is the difference between Dry Canning and Dry Packing?

While there are many well-intended people out there, sadly there is so much confusion circulating the internet, I decided to clear things up a bit…

For starters, the bulletin released a couple years ago by the El Dorado County UC Master Food Preserver Program is one of these “well intended” announcements. Sadly, bulletins like this distort reality by comingling terms and misrepresenting facts, which fuels the divide amongst canners.

Let’s break it down…

For starters, there is a gross misunderstanding of what dry packing truly is within the realm of home canning. Dry packing has been used since home canning began. This method of filling jars is nothing new to home canning and it certainly is not unsafe, or we would not have successfully used this familiar jar packing method for so long.

What is the dry packing method?

As explained in my blog, Dry Packed Potatoes Canning Recipe, the method of dry packing food in jars is merely eliminating the instructional step of covering said food with water. We are simply raw packing the food into jars without water, filling each jar to the required headspace, then processing the filled jars for a specified length of time in a pressure canner, or water bather.

For example, we do this when packing jars full of raw, uncooked meat, poultry, and fish. Many of us simply call it “raw packing” however, I redefined this method of jar packing as “dry packing” to differentiate it from the standard norm. This differentiation isn’t new, it has merely just been given its own terminology. Doing so doesn’t suddenly make this method of jar packing unsafe.

Where is the confusion coming from?

It is obvious the term dry packing has somehow been confused and comingled with the unsafe practice of “dry canning”. Confusing two totally different methods of food preservation, comingling of terminology, wielding fear as a weapon, and telling home canners they are not smart enough to understand science and math, opened a dangerous floodgate of misinformation, disrespecting home canners and recipe creators across the globe.

So let me end the confusion here and now…dry packing food in jars is NOT the same as dry canning in an oven.

What is “Dry Canning” and How did it get its Start?

“Dry canning was a short-lived concept of using a residential oven to process food in jars for long-term storage.”
-Diane Devereaux, The Canning Diva®

Believe it or not, using a residential oven to preserve food in jars became popular around the turn of the 20th century in 1905. Not because it was a proven food preservation method, but because it was a way to keep your kitchen clean with less prep time all the while keeping the color of the fruit brighter and the fruit’s integrity intact.

While this oversimplified logic to achieve the same outcome as water bathing was applied, these individuals did not understand or consider the composition of a glass canning jar. Failing to take into account how a glass jar would respond to a dry heat environment was a huge mistake. Dry heat from an oven cavity is substantially hotter than wet heat used in a water bather or a pressure canner. The outcome of using an oven’s dry heat to process glass canning jars was explosive. Literally.

In 1908 there were documented cases of people getting terribly burned by exploding fruit in jars. And here you thought pressure canners were dangerous. Ultimately, the use of residential ovens for canning raw ingredients in jars was deemed unsafe due to the glass not being able to withstand a dry heat environment causing explosions. In some cases, the glass exploding inside the oven cavity led to the oven’s glass door shattering all over the individual’s kitchen. Point blank, glass canning jars are not built for preserving foods using hot dry heat generated from an oven.

By 1945 countless American articles and radio advertisements warned people about the dangerous results from such explosions. Many people suffered severe burns, loss of eyesight, received serious cuts and other serious injuries not to mention the damage to their ovens and their homes.

Acknowledging the Difference

But this misuse of canning jars is not what we are doing when we are dry packing food when home canning. We are not using dry heat from an oven to process these recipes. We are using wet heat just like all our home canning recipes. So, regardless if we dry pack raw chicken, potatoes, or fish into a jar, without adding water, we are still using wet heat to process each jar of food.

Further, we are not preserving dried food in jars either! The unfounded notion that without adding water to the jar its contents are without moisture is just as ridiculous as it is untrue. There most certainly is moisture in the foods being dry packed and preserved, we aren’t canning beef jerky for crying out loud. There is moisture in the food which is why you will often see water droplets inside the top of the jar after processing. It is also why you see a collection of water and food particulates at the bottom of the jar after processing.

It is obvious the interior contents of the jar are not without moisture debunking the rumor the heat during processing failed to penetrate the food because it was “dry”. Yes, you can have complete thermal transfer of heat throughout every fiber of the meat, vegetable, poultry, or fish without added water.

Dry Heat, Wet Heat and Glass

While many are misrepresenting dry packing as using “dry heat”, the reality couldn’t be further from truth. In its simplest form, using wet heat to cook and process food in jars is accomplished because there is hot water and/or hot steam in the canner vessel and moisture within the fiber of the food.

Dry heat used in cooking is hot dry air without any moisture. It does not mean the food itself is without moisture, just the heat used is dry and without moisture. We typically cook using dry heat and the heat source is situated either above or below the food.

The most common use of dry heat is cooking on a stovetop. The heat source is below the food. Another common use of dry heat is using a conventional oven to bake, roast, or broil. In an oven, the heating element can be above or below the food and the dry heat can be circulated throughout the oven cavity with a fan or ventilation system.

At no time during the water bathing or pressure canning process are we using dry heat to process food in jars. The only occurrence of dry heat when pressure canning would be if the pressure canner ran dry during operation. Meaning, the canner expelled all of its water from within the vessel. This is why we do not vent our pressure canner for longer than 10 minutes.

For those of you who are new to pressure canning, when a pressure canner runs dry the glass jars usually shatter, and the food is always burnt. Why? Because the environment changed from wet heat to dry heat, glass canning jars cannot handle dry heat nor its vast increase in temperature compared to wet heat.

Annealed versus Tempered Glass

Dry heat is hotter than wet heat. This why an oven heat is so much harder on glass canning jars compared to wet heat when water bathing or pressure canning. It is for this reason a glass canning jar cannot be considered, or used, as bakeware.

Many of us cook and bake with glass bakeware in our home ovens. To accomplish this safely we use glass bakeware products like Pyrex which are created from tempered glass designed to withstand higher temperatures and temperature differentials. Essentially, tempered glass has been strengthened to be upwards of five times stronger than untreated, standard glass.

Despite what many believe, a glass canning jar is NOT made from tempered glass. A glass canning jar is made from annealed glass. Annealed glass is simply standard glass. While it is strengthened to make it durable, it is not created equal to tempered glass, therefore it will stress crack when exposed to high heat.

Don’t believe me? The most well-known jar manufacturer states so very clearly:

“We do not recommend baking in any size or shape of Ball or Kerr canning jars. The glass used for Ball and Kerr canning jars is not tempered for oven use and is not meant to be used as bakeware. The jars are safe to use for home canning recipes, cold or room temperature food storage, cold beverages, and crafting.”

This information can be found on their FAQ of their website under: Can I use the jars in the oven for baking?

The Difference is Clear

You can clearly see the vast difference between dry canning and dry packing. It is amazing to me that an entity who has been elevated to an authority-like status could be so intentionally misleading, inaccurate, and divisive.

At the end of the day, I believe I said it best in my BBC World View interview on The Food Chain podcast this past January 2024:

“I don’t want to see this divide. If there is one thing, we can all come together on, it should be food.” -Diane Devereaux, The Canning Diva®

If an extension office, or Master Canner, is so adamant that dry packing potatoes is “unsafe”, why don’t they test it themselves? Instead of writing misleading bulletins aimed at confusing and dividing the home canning community, just put the entire topic to bed once and for all and test it.

In the meantime, I will continue to advance this time-honored craft forward by being innovative and by expanding upon existing science and math to create delicious safe recipes for home canners across the globe.

Have a blessed canning season and keep on keepin’ on!

Happy Canning!
Diane, The Canning Diva®