Jar lids play a vital role in home canning. In addition to ensuring that the preserved food stays in the jar, they also keep that food sterile after the jar has been processed by keeping nasties from re-entering the jar.
Over the course of time, several lid systems (technically referred to as “closure” systems) have been tried. Though many look “nifty”, only a few have passed science-based lab-testing for assured food safety.
A lid closure system must perform the function of creating an effective, lasting, reliable vacuum seal that allows a way for you to confirm it is sealed after canning, and is remaining sealed during storage.
- 1 Mason jar lids
- 2 Standard North American Mason Jar Mouth Sizes
- 3 Mason jar lid (two-piece lid system) size comparison
- 4 The USDA position on lids
- 5 Why do USDA and NCHFP like two-piece lids?
- 6 Lids on tops of new jar packs
- 7 How do the “flat metal with rubber rings on them” lids work?
- 8 The metal disc lids are one-time use only
- 9 No longer any need to boil the Mason jar lids, or even warm them
- 10 Can you re-use prepared but unused Mason jar lids?
- 11 With the metal canning lids, a ping is usually indicative of a seal. But don’t count on it.
- 12 When metal Mason jar canning lids buckle
- 13 Lids have to vent air during processing
- 14 Lids coming off in storage
- 15 A sealed lid on a jar does not necessarily equal safety
- 16 If you move your sealed Mason jars to a different altitude, will they come unsealed?
- 17 Is it safe to decorate canning jar lids?
- 18 What is the shelf-life of the unused lids?
- 19 The great canning jar lid shortage of 1975
- 20 Further reading
- 21 In other words
- 22 Lid Related Topics
Mason jar lids
When referring to the two-piece lids that go on (a) Mason jars in North America, (b) Kilner preserving jars in the UK, (c) Agee / Perfit jars in New Zealand, (d) Leifheit preserving jars in Germany, and (3) Le Parfait Familia Wiss jars in France, people generally loosely refer to both pieces — the flat metal part and the ring band — collectively as the “lid.”
The two-piece metal Mason jar lid system is also referred to as a “self-sealing lid.”
The lid of a Mason jar is actually just the flat part
In actual canning talk, (as well as in practice), the lid proper is actually just the flat metal disc by itself. The screw-on ring band only has a very temporary purpose: to hold and press down the flat metal part during processing until a seal of the lid is effected.
The misconception goes way back. In 1986, Nancy Hudson, a former extension agent in Greene County, Ohio, explained:
Many consumers are under the misconception that the ring band maintains the seal. Reality is the vacuum within the jar causes the jar to seal. The ring band has no function once the jar is removed from the canner and allowed to cool.”1
Who makes Mason jar lids?
You can also buy no-name ones in large sleeve quantities of a couple hundred at a time (from places such as Lehman’s and Cane Creek Market in Tennessee, who both ship.) Walmart also sells its own brand of metal jar lid closures under the name of “Mainstays.”
What are Mason jar lids made of?
This may vary by manufacturer. As far as Jarden’s three main lids go — Ball, Bernardin and Kerr, which are identical — they are made of thin steel:
Jessica Piper, from the Ball company which makes lids, says that “[the lids are] a tin-plated steel..” 2
How does a Mason jar lid work?
Putting Food By says,
This metal lid called ‘dome’ or ‘self-sealing’ or ‘snap’ by the individual makers, but of one basic design—is a flat metal disc with its edge flanged to seat accurately on the rim of the jar’s mouth; the underside of the flange has a rubber-like sealing compound; the center surface next to the food is enameled, often white.” 3
When a metal lid has effected a seal, it will curve down in the centre, and there will be no up and down movement in the lid when you press on the lid with your finger. The vacuum seal inside the jar sucks the lid down, creating the seal. (Technically, because air has been pushed out of the jar, the pressure inside the jar is less, so the greater pressure of the air outside the jar is pressing and holding the lid down.) Another word for this type of seal is “hermetic”. It means completely air tight.
Who created the modern Mason jar lid?
The metal lid with attached rubber ring on the underside was created by the Kerr company in 1915; Ball only switched to that format in 1934. 4
Standard North American Mason Jar Mouth Sizes
There are two standard Mason jar lid sizes: 70 mm (2 3⁄4 in) referred to as “regular mouth” lids and 86 mm (3 3⁄8 in) referred to as “wide-mouth” lids. If you are thinking purely in metric, it’s probably cleaner to just think 70 and 85 mm.
Note that the width of the lid / jar mouth size is independent of the volume of the jar: there is no correlation.
The wide-mouth North American lids from Jarden (Ball, Bernardin, Golden Harvest and Kerr), as well as the re-usable wide-mouth lids from Tattler, fit 85 mm Agee and Perfit jars in New Zealand, Leifheit preserving jars in Germany, and appear to fit Kilner preserving jars as well.
Mason jar lid (two-piece lid system) size comparison
- Agee Australian: 80mm
- Agee NZ: 86mm
- Ball: 70mm / 86mm
- Bernardin: 70mm / 86mm
- Frutta del Prato (70 mm – some jars)
- GEM: 78mm
- Kerr: 70mm / 86mm
- Kilner DualPurpose: 83mm / 85mm
- Kilner Rayware: 70mm
- Le Parfait Familia Wiss: 82mm / 100mm / 110mm
- Leifheit: 85mm
- Perfit seal: 86mm
- Quattro Staggioni: 56 mm / 70mm / 86mm
Source: http://www.seco.com.au/sustainable_living/viewtopic.php?t=715#p4575. Accessed June 2015.
86 mm and 85 mm lids are interchangeable. Some sources say that 86 mm lids should also work on jars indicated as having 82 mm and 83 mm mouths, but we have not had occasion to test this (as of July 2015.)
If you have older Agee jars and are looking for the 80 mm lids for them, some people suggest looking at either 78 mm GEM lids from Bernardin, or 82 mm lids from Le Parfait Familia Wiss. We have not been in a position to evaluate this for ourselves.
The USDA position on lids
No actual brand or type of lid closure is officially approved by the USDA (United States Department of Agriculture) or the NCHFP (National Center for Home Food Preservation.)
There are, however, types of jar closures that they pro-actively recommend against. Note that in canning lingo, “recommended against” is expressed by the phrase, “”not recommended.”
A USDA Extension agent, Patti Griffith at the University of Wyoming, sums up the USDA’s position:
Jars requiring a zinc cap and jar rubber or jars requiring a glass lid, wire bail, and jar rubber have not been recommended since 1989 because there is no definitive way to determine if a vacuum seal is formed.” 5
Why do USDA and NCHFP like two-piece lids?
Even though the USDA doesn’t actually approve any closure system, the current USDA recommendations are based on a two-piece metal lid system, with a flat metal lid and a ring band to hold that lid in place during processing.
The two-piece lid system:
- Is easy for people to understand how to use;
- Has a documented and research-based, lab-tested track record of sealing reliably;
- People can easily tell if the lids sealed the jars (grasp edges of flat lid with ring off and try to lift.) 6
The USDA / NCHFP don’t yet have enough experience with some alternative lid systems to endorse them the way they have the two-piece metal lids:
That doesn’t mean you won’t have success with other lids. What you will see in the USDA guide is: this is the best choice. It doesn’t say it is the only choice or the only safe choice, it merely says this is the best choice, and that’s because that’s what we have the most experience with. We are actually here at this center just starting a student study to kinda look and get more experience with the plastic reusable lids in the marketplace.” 7
In a 2013 webinar, Elizabeth Andress, director of the National Center for Home Food Preservation, seemed to — intellectually at least — keep the door ajar for other lid possibilities: “Then you prepare your canning lids and ring bands or rubber rings whichever lid style you are using by the manufacturers instructions.” 8
The USDA’s beef with glass lids and rubber rings is not that they are unsafe per se, but rather, it’s that they think it’s a performance issue: that it fails to seal too often. “Both glass and zinc caps use flat rubber rings for sealing jars, but too often fail to seal properly.” 9
That’s not just unfounded opinion, either. Remember that the USDA’s home canning division (under various names) has been there for as long as home canning has been going on, and they’ve seen it all. Here’s an observation from them in 1940 about spoilage from the older closure systems in use at that time:
They found considerable food spoiled because women had used worn or cracked rubber rings on their jars, or bent covers that meant leakage and a chance for spoilage to get in.” ((USDA Radio service. Housekeeper’s Chat. 30 April 1940. Page 2.))
Lids on tops of new jar packs
Ball, Bernardin, Kerr, Leifheit, Kilner, and a few others ship their jars with the two-piece lids already in place on top of the jars. (The exception is Le Parfait, with its brilliant solution of simply shipping the lids upside down on the jars to prevent this.)
Jessica Piper, spokesperson for Ball, says:
When you buy a new case of jars, that have the lids on them, a lot of people notice that the lids might have an indentation on them, are they safe to use, should they use them any differently? We implemented a packaging change ten years ago, maybe even longer, to this simple half pack, corrugated with the plastic seal with the bands already on the jars…. and we did a lot of testing before we even brought it to market, so we’ve been getting this question for a long time, and you know the lids themselves will sometimes ‘seal’ because of the temperature changes so you may actually have bought a case of jars at your grocery store and been driving them home in the heat of the summer and hear ping, ping, ping…simply because of the temperature change and because you do get a low-vacuum seal on those jars which can cause a bit of a ring impression. So the lids are indeed safe to use.. they have not gone through the actual canning process for that duration in a hot water bath or in a pressure canner, they have not gone through that.” 10
[even if the indentation is really deep, it doesn’t matter] because they haven’t gone through the processing method, so our quality assurance lab has done an extensive amount of testing on our lids…” 11
I’ll also highlight too, while I’m thinking about it, lids on new jars, if they are stuck or a little difficult to get off, don’t worry, they are safe to use, simply wash in hot soapy water…” 12
How do the “flat metal with rubber rings on them” lids work?
The USDA says,
The common self-sealing lid consists of a flat metal lid held in place by a metal screw band during processing. The flat lid is crimped around its bottom edge to form a trough, which is filled with a colored gasket compound. When jars are processed, the lid gasket softens and flows slightly to cover the jar-sealing surface, yet allows air to escape from the jar. The gasket then forms an airtight seal as the jar cools.” 13
The U.S. Department of the Treasury even weighs in:
The common self-sealing lid consists of a flat metal lid held in place by a metal screw band during processing. The flat lid is crimped around its bottom edge to form a trough, which is filled with a colored gasket compound.” 14
The metal disc lids are one-time use only
Jessica Piper of Ball says,
[why are the lids one-time use] The one-time use, after they have gone through the processing method, you get a really tight vacuum seal…once it’s gone through that, we can’t guarantee it’s going to work if you were to attempt to use it again, which is why it’s a one-time use lid, you really got a good impression and it went through all that heat processing, so we don’t recommend [using the lid again.]” 15
No longer any need to boil the Mason jar lids, or even warm them
Pre-warming Mason jar lids was recommended up until around the 1970s for the sake of the material used in the gasket ring on the underside of the lids. After the 1970s, the material used to make that gasket ring was changed and boiling or even heating no longer had any effect one way or the other. However, it was hard to change canning advice floating around out there.
Jessica Piper of Ball says,
The pre-warming was recommended for that red gasket. A long time ago, they were made of latex. So back in those days, you did have to pre-warm that latex to soften it up to get a good seal but with the plastisol, which is that red ring that you see now, there’s no longer a need for pre-warming, and that was something we changed all the way back in 1969. The plastisol itself has had zero changes for decades upon decades upon decades.” 16
In fact, they recommend AGAINST boiling the lids:
However we have always recommended that you do not boil your lids. Boiling can over soften that compound and cause lid failures or your seals to not seal at all. 17
Just wash the lids first to get any factory dust off them:
Wash lids in hot soapy water and set aside until ready to use….. When we initially posted that little tidbit on Facebook a while back, we had some consumers mentioning that they were washing their lids and bands in the dishwasher, I do want to state you should probably stay away from that, just simply hand wash, because it can be a little too abrasive and too hot in your dishwasher and cause those lids to rust or corrode.” 18
Ball was telling people in writing to go ahead and heat lids as recently as the 36th edition of the Blue Book in 2013:
Home canning lids with sealing compound must be heated for 10 minutes before using to help lids achieve a vacuum seal. Place lids in water to cover and bring water to a simmer (180 F / 80 C), keeping lids in simmering water until ready for use. Remove lids one at a time for caning. Lids can be heated in a saucepan on a cook-top. Or, in a slow cooker that has a temperature control that can maintain 180 F / 80 C. Note: Overheating lids by boiling can result in seal failure.”19
For more on this topic, see: Sterilizing canning lids and jars.
Can you re-use prepared but unused Mason jar lids?
There is no need to boil or even warm lids before use, but some people still do, and wonder: if they didn’t end up needing them for this round of canning, can they use them in the future instead?
If you heated metal lids in water, but didn’t end up needing them or using them, you can let them dry, and use them for your next batch of canning.” 20
Jessica Piper, Ball spokesperson, says:
If you do choose to simmer [the lids], people sometimes worry if they can use them again now that they’ve simmered them. Absolutely. You can still use those again. You’ll just want to make sure they are thoroughly dried [before] they are stored. 21
With the metal canning lids, a ping is usually indicative of a seal. But don’t count on it.
The National Center for Home Food Preservation says that a ping means you have a seal:
When the two-piece metal lid system is used: Listen for “pop.” As jars cool, listen for a popping sound. This indicates that jars are sealing.” 22
Jessica Piper of Ball, however, says that’s not always the case:
[Customer would like to know why does she sometimes not hear a ping] As exciting as the ping is, it doesn’t necessarily means your lids are sealed. Sometimes you’ll hear that, sometimes you don’t, you don’t want to use the ping as a factor for knowing if your lids have sealed or not. They can actually, believe it or not, seal and unseal and seal and unseal a couple of times while they are cooling on your counter, just depending on the temperature, that has happened here before too. So the ping is not a clear sign. So don’t get discouraged if you don’t hear it. That has nothing to do with the lid’s capability to seal.” 23
In fact, your lids may even sometimes “ping” or appear to seal before you get the jar into the canner:
What should I do if the lids seal before I get the jars into the canner for processing? If lids seal (‘pop’) before jars go into the canner, the jars must still undergo the normal processing required for that product. A ‘seal’ that forms before processing is very weak and the exhausting of air and a complete vacuum has not occurred. Processing will allow the formation of a complete vacuum which is necessary to insure a proper seal. To help eliminate the problem of a seal forming before processing, work as rapidly as possible to get filled jars into the boiling-water canner or steam pressure canner. Be sure to fill and cap only one jar at a time. ”24
When metal Mason jar canning lids buckle
Jessica Piper of Ball covers this topic:
[What happens when the lids crinkle, why does that happen?] Buckling. Two different factors that can cause buckling. … if you are pressure canning, and you bring the pressure back down to zero too quickly, that can cause the lids to buckle, too much pressure, the pressure change, the lids are actually designed to buckle when the pressure gets too great versus the glass breaking… so that’s a good thing, you want it to buckle, because now you know that there is something wrong in your process, and when your lids do buckle, you actually have to reprocess, you have two hours to reprocess. Something else that can cause that is improper headspace….headspace is quite important for the food expansion inside of your jar, as well as making sure you get the right vacuum, and a good strong vacuum…. you want to make sure that you remove your air bubbles, again if the headspace is incorrect, and if you don’t remove air bubbles, that also can affect your headspace, your total headspace, so that can cause the lid to buckle too, there’s no room for your food to expand, and there’s pressure building up in there. And boiling your lids can actually be part of the problem because if you oversoften that compound it will adhere to your lid [Ed: jar?] too soon [Ed: before proper venting happens?] and pressure will build up … and lastly, if your band is too tight. So the whole purpose of the band is to simply act as a place holder, you put your lid on your jar, and then you adjust your band to fingertip tight, so if you do it too tightly, again you get too much pressure, that lid is going to buckle to try to release that pressure, so the lid should be able to hover a little bit over your jar to allow all the gases, oxygen to evacuate and then when it comes out of the canner and you get that change in temperature it’s going to seal… So those are a couple factors [in buckling]: headspace, removing air bubbles, boiling lids, bring down your pressure too quickly, are all four very common reasons for lids to buckle.” 25
Linda Ziedrich adds,
Overtightening the ring could cause the lid to buckle or the jar to break…” 26
Lids have to vent air during processing
Oxidation causes food to spoil or degrade in various ways, either in appearance or in nutrient value or both. It’s important that, during processing, a lid allow aid to escape from the jar:
Canning lids that are applied correctly allow oxygen inside the jar to escape during the canning process, before the jar seals.” 27
Lids coming off in storage
Jessica Piper of Ball gives an explanation of lids coming off of home canned goods in jars in storage:
…consumers will call us because they’re like, oh, the lids came unsealed. Your lids are, you know, they came unsealed. Well, one of the questions we’ll ask is, how long after you removed them from the canner did they come unsealed? And they’re like, oh, a week, three months or, you know, it varies. And that’s – I mean, that’s a pretty clear sign right there that there was a miss in the process, and they’ve made a beautiful buffet of food for these microorganisms, bacteria to grow on. And they create gases as they’re eating away, and that’s what’s going to pop the lid off.” 28
Kerr in 1948 also pointed out another possible cause: damaged jars.
…cracks in jars which permit slow release of seal.” 29
A sealed lid on a jar does not necessarily equal safety
Does a sealed lid on a jar mean it’s safe? We’ll let Washington State University Extension Service handle this answer:
Absolutely not. The sealed lid on a canning jar simply keeps the food safe. Safety of the contents depends on having a recipe that was developed and tested for canning, accompanied by a processing time in either the boiling water canner or pressure canner, which provides the heat necessary to create a shelf stable product. Processing times for foods are determined by scientists under laboratory conditions.
There are several critical measurements done in the laboratory, including water activity, pH, and the rate of heat penetration. All are factors used to determine the thermal death time curve (TDT) for each product. This data is used to establish a processing time for the food. The sealing of the lid simply indicates the oxygen has been vented out of the canning jar and a vacuum seal has been created. In other words, the processing makes it safe, the seal simply keeps it safe.”30
If you move your sealed Mason jars to a different altitude, will they come unsealed?
(A) I’m moving out West and I’ll be taking many home-canned foods with me. Will I have any problems with jar seals when I move them to a higher elevation? (A) As long as foods were properly canned and a good vacuum was achieved, you should not have any problems. If jars have a weak vacuum, they can lose their seal if moved to a higher elevation. If this occurs, discard the food. Source: Pennsylvania State University Workshop on Home Food Preservation, May 1987.31
Is it safe to decorate canning jar lids?
Jessica Piper, spokesperson for Ball, says yes, it is fine to decorate lids:
“[Is it safe to decorate the lid for gift giving?] Sure, but you want to make sure that after you process, you allow your jar to completely cool, so 12 to 24 hours after removing from your canner, that’s when you are going to want to check your seal….and make sure your jars are clean, at that point you can certainly add labels to the jar, to the lid, a lot of people like to use permanent marker on there, that’s fine.. the reason I say to wait your 24 hours is because you don’t want to fiddle with the lid while it still could be cooling and that could actually affect your seal and cause it to unseal… I would just be very conscious of not knocking your jar around a whole lot or fidging with it too much but putting a bow on there.. you certainly can do those things..” 32
What is the shelf-life of the unused lids?
As a reminder, “lids” here refers to the flat metal discs with the rubber gasket ring on the underside. It does not refer to the canning rings.
Jessica Pipe from Ball says,
We recommend using the lids within a year of purchase, although you can still use them 3 to 5 years later. ”33
The lids don’t really have a shelf life per se…. whatever’s the oldest, use that first… Again, we recommend within a year, but if you have some that are 3 to 5 years, you’re going to be okay.” 34
The USDA says,
Gaskets in unused lids work well for at least 5 years from date of manufacture. The gasket compound in older unused lids may fail to seal on jars.” 35
In 1948, Kerr lids had an indefinite shelf life before use — as far as Kerr’s advice went, anyway:
Will Kerr Mason Lids purchased one year be safe to use in the next year’s canning? The sealing composition in the lids does not deteriorate rapidly and if the lids are stored in a cool, dry place they will keep in good condition.” 36
Note that the shelf life of when to use the lids by has nothing to do with the shelf-life of the lid after use. Jessica Piper says:
The lids themselves, the shelf-life for when to use them, that has nothing to do with the year’s shelf life of how long they’re good once you’ve actually preserved with them.” 37
Once sealed on a jar, the seal of a lid should in theory be good for decades, if not centuries.
The great canning jar lid shortage of 1975
In America, in 1975, there was the great canning jars metal lids shortage.
Canning lid shortage
To the Editor: Why are there no canning lids available in Wisconsin? The companies that make the lids knew after last year they had to make more for 1975. Still there are none around. When I inquire at the stores they say they have none. The companies are sending them south because their food comes in first. Well, fine they had all winter to send south. I have a large garden and asparagus, rhubarb and, soon strawberries will be in. My peas are blooming now. What am I to do? I usually can about 500 jars and fill two freezers. I have been fighting this food battle all my life, but this is the first time I am unable to do anything about it. What the stores are doing now is getting the ladies all upset because the lids are not in while they raise the prices of vinegar, salt, sugar, spices and other canning supplies. This is sure the year of the Big Rip Off.” [ MARY BERGLES, Route 2, Franksville. Racine County, Wisconsin. In: Racine Journal Times June 23, 1975. Letters to the Editor. Page 8. ]
Around-The-Clock Production Doesn’t Ease Jar Lid Shortage
Ball Corp., one of the nation’s leading producers of home food preservation supplies, says it is continuing to manufacture replacement lids for home canning on an around-the-clock basis, seven days a week, at its Muncie, Ind. factory. Despite this production schedule, in effect since Jan. 2 of this year, the company is not able to meet the continuing nationwide demand for its products. John W. Fisher, president of the firm says, ‘An investigation is currently under way, with auditors checking the production records of the firm, to determine if reports of employee theft from production lines of the firm are true and influencing the nationwide shortage. Home canners bought more of the company’s production during the first quarter of this year than ever before in the 90-year history of the corporation.
The firm is presently shipping five replacement caps or lids for each lid which is shipped with a complete jar and cap unit, according to a company spokesman. Ball home production will not be greater than it was in 1974 because of the apparent plentiful supply of jars already in consumers’ homes or available in the marketplace. According to Fisher, at the beginning of 1973 there were only two manufacturers of the complete canning unit (jar, lid, and ring). This year there are six other manufacturers which have the complete unit for sale and still the supplies are not meeting demands. [ Beckley, West Virginia: Post Herald and Register. 3 August 1975. Page 20. ]
It was this shortage that, reputedly, inspired the creation of Tattler re-usable lids around that time as an alternative.
The lid shortage impacted Canada as well, and outraged home canners in Canada had the most senior people in government investigating the issue. See: the Great Canadian Lid Shortage of 1975.
Penn State Extension. How to Ensure a Good Seal. 16 August 2012. Accesssed January 2015 .
In other words
Words for the two-piece lid system in other languages.
- Lid: couvercle (French), Ersatzdeckel (German) Deksels (Dutch)
- Canning ring: bague de serrange (French), Schaubringe (German), schroefringen (Dutch)
Hudson, Nancy. New research gives tips on using jars and lids. Xenia, Ohio: Daily Gazette. 7 April 1986. Page 6. ↩
Hertzberg, Ruth; Greene, Janet; Vaughan, Beatrice (2010-05-25). Putting Food By: Fifth Edition (p. 65). Penguin Publishing Group. Kindle Edition. ↩
Accessed July 2015 at http://www.freshpreserving.com/sites/all/themes/freshpreserving/library/TimelineOfLidTechnology.pdf ↩
Griffith, Patti. The time is ripe for summer melons. University of Wyoming Cooperative Extension Service. From series “Canner’s Corner: Enjoying Summer’s Bounty.” Issue Two. MP-119-2. Accessed March 2015 at http://www.wyomingextension.org/agpubs/pubs/MP119_2.pdf ↩
Andress, Elizabeth. “History, Science and Current Practice in Home Food Preservation.” Webinar. 27 February 2013. 1:14:00. Accessed January 2015. ↩
United States Department of Agriculture (USDA). Complete guide to home canning. Agriculture information bulletin No. 539. 2015. Page 1-10. ↩
United States Department of Agriculture (USDA). Complete guide to home canning. Agriculture information bulletin No. 539. 2015. Page 1-15. ↩
Ball Blue Book Guide to Preserving. Daleville, Indiana: Hearthmark LLC. Edition 36. 2013. Page 11.)
It’s only in 2014 that their written advice in the Blue Book (37th edition) changed:
Wash lids and bands in hot, soapy water. Do not use abrasive materials or cleansers that might scratch or damage the coatings applied to the lids and bands. Rinse them under hot water. Dry lids and bands and set aside until they are needed.” ((Ball Blue Book. Muncie, Indiana: Healthmark LLC / Jarden Home Brands. Edition 37. 2014. Page 12. ↩
National Center for Home Food Preservation Self-Study course. Module 2. “General Canning: Post-processing Checks” ↩
Missouri State Extension. MSU “Hot Lines” #81-9. Accessed August 2017 at http://missourifamilies.org/quick/foodsafetyqa/qafs108.htm ↩
Ziedrich, Linda. The Joy of Pickling. Boston, Massachusetts: The Harvard Common Press. 2009. Page 25. ↩
National Center for Home Food Preservation Self-Study course. Module 1. “Introduction to Food Preservation: Major Causes of Food Spoilage” ↩
Washington State University Extension Service. WSU Extension Q&A. Kennewick, Washington: Tri-City Herald. 31 July 2016. Accessed October 2016 at http://www.tri-cityherald.com/living/home-garden/article92516402.html ↩
University of Missouri Extension. Accessed May 2017 at http://missourifamilies.org/quick/foodsafetyqa/qafs16.htm ↩
Jessica Piper. Video: Canning Lids 101. 17:54. Accessed March 2015 at http://ball.yourbrandlive.com/c/lids/. ↩
United States Department of Agriculture (USDA). Complete guide to home canning. Agriculture information bulletin No. 539. 2015. Page 1-15. ↩