When canning, it becomes a vital element to save time and ensure you fully utilize you canner space with each batch. That is why it can be a question many canners face when working with smaller jar sizes, can I stack them?
This is often called Double-decking or double-stacking in canning manuals. Double-decking is the practice of running a canner with two layers of jars in it, one on top and one on the bottom, with a platform of some sort in between.
You just need some kind of ventilated metal platform between the two layers. Don’t stack jars directly on top of each other. The purpose of the platform is to stabilize the top row of jars, so that they don’t tilt over or fall over on their sides. That would interfere with the sealing, and possibly allow the jars to bang about inside the pot. The purpose of the platform being “ventilated”, as in having holes or perforations or spaces in it, is to allow boiling hot water, or steam, to move freely throughout the pot.
As a general rule you will always want to double check your canner manual, but here are some facts and tips about double-decking in a canner.
Double-Decking for Water-Bath Canning
Whether double-decking is endorsed or not for water bath canning depends on who you ask.
The National Center for Home Food Preservation says that double-decking is fine for both water-bath canning and pressure canning:
“Can two layers of jars be processed in a canner at one time? Yes, two layers can be processed at one time, in either the boiling water bath or pressure canner. Place a small wire rack between the layers so water or steam will circulate around each jar. Make certain that the water covers the top of the jars by 1 inch [ 2 ½ cm] in a boiling water bath canner. The pressure canner should have 2 to 3 inches [ 5 to 7 ½ cm] of water in the bottom.”
NCHFP. Canning FAQ #8. Accessed November 2022.
The University of Missouri Extension says yes as well:
Q. Can I process two layers of jars in a canner at one time? A. Yes, you can process two layers at one time, in either the boiling water bath or pressure canner. Place a small wire rack between the layers so water or steam will circulate around each jar. Make sure the water covers the tops of all jars by 1 inch in a boiling water bath canner. The pressure canner should have 2–3 inches of water in the bottom.”
Home Canning: Questions and Answers. Mississippi State University Extension. Publication 993 (POD-01-16). 2016. Page 5. Accessed November 2022 at https://extension.msstate.edu/sites/default/files/publications/publications/p0993_0.pdf
The University of Wisconsin Extension Service, however, recommends against double-decking for water-bath canning:
“We don’t recommend stacking jars in a boiling water canner because the water movement may tip the jars.”
Presto answers this question on its FAQ page in the canner use section, question 3:
“For some canner models, it may be necessary to double-deck pint or half-pint jars to reach the maximum capacity of your canner. It is recommended that you stagger the jars by placing one jar on top of two. The canning rack which accompanied your Pressure Canner must be placed on the bottom of the canner to prevent jar breakage. It is not necessary to use a rack between the layers of jars. However, if you wish to do so, go to Parts & Service and search for your canner’s accessories to order a rack.”
Source:https://www.gopresto.com/content/s/canning-faq#:~:text=It%20is%20recommended%20that%20you,between%20the%20layers%20of%20jars.
HealthyCanning.com tested the capacity of the Presto 23 quart (with cold tap water and empty jars half-liter / US pint with lids but without actually canning), and weight consideration aside, if it is standard height half-liter (US pint) mason jars that you are stacking, then no, the Presto 23 quart pot is not tall enough for water bathing double-decked jars of that standard height profile size without the water boiling over constantly onto the stove — and that is one of the tallest pots that the average home canner is likely to have, anyway. So, it’s a non-starter.
DOUBLE-DECKING IN WATER-BATHING DOES NOT AFFECT PROCESSING TIME
Double-decking for water-bathing would affect the amount of water needed, clearly. But it would not affect the processing time. You still need to follow the recommended processing time for your tested recipe: no more, no less.
DOUBLE-DECKING FOR PRESSURE CANNING
All authorities endorse the practice for pressure canning. It’s considered a safe practice, and even safe, cautious canners routinely do it. There is no issue with it as far as food product safety or quality goes.
The main point most make though when double-decking is to stagger the jars between the layers and utilize a rack each time.
The reason you need to stagger the jars is to distribute the weight. You don’t want too much weight in one spot preventing air from escaping out of the lids in jars below during processing.
For pressure canning, there are many different unofficial double-decking and even triple-decking configurations that people do in Presto canners.
DOUBLE-DECKING IN PRESSURE-CANNING DOES NOT AFFECT PROCESSING TIME
Double-decking for pressure canning does not affect the water required or the processing time. You still put in the amount of water recommended by the canner maker — no more, no less. And, you still need to follow the recommended processing time for your tested recipe, no more, no less.
| Capacity in US jars | Capacity in metric jars |
|---|---|
| Regular Mouth 12 x US ½ pint regular-mouth jars 10 x US 1 pint regular-mouth jars 7 x US 1 quart regular-mouth jars Wide Mouth 8 x US ½ pint wide-mouth jars 8 x US 1 pint wide-mouth jars 7 x US 1 quart wide-mouth jars | Regular Mouth 13 x 250 ml regular-mouth jars 9 x 500 ml regular-mouth jars 7 x 1 litre regular-mouth jars Wide Mouth 8 x 250 ml wide-mouth jars 8 x 500 ml wide-mouth jars 7 x 1 litre wide-mouth jars |
[Ed: it actually holds 14 of the Kerr style jam jar half-pints in each layer.]
DOUBLE-DECKING FOR STEAM CANNING: NO
It is physically possible to stack some low-profile jars in the Victorio multi-canner steam canner in a stable and secure manner, using a perforated divider plate from a pressure canner.
But, is it safe in processing terms to do so? There has not been any studies to see the effectiveness of the steam flow for it to be recommended at this time.
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