Commercial Canning and How It Shaped Home Canning Practices

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I hath gone down a rabbit hole.  

What started with reading about commercial botulism outbreaks in the 1900’s when commercial canning was relatively new snowballed into researching the differences between commercial canning, also known as retort canning, and what we do at home.  Which led me to learning that these commercial botulism outbreaks paved the way for what we known now as modern home canning techniques.  In the 1930’s, home canners didn’t really have many guidelines outside of passed down knowledge (that wasn’t being shared anymore because canned food in stores is way easier) and they were trying to mimic what they were seeing from commercial canneries and experiencing lots of food lost to spoilage and occasional botulism.  Access to information and data was hard to come across.  In response to these things, the USDA got involved, with Bulletin number 930 and the formation of the NCHFP (National Center for Home Food Preservation) decades later on to help distribute this information and data in one place for people to access.  In 1946, home canning became a necessity for war time.  Most of this blog post is going to be talking about low-acid foods and pressure canning low acids foods (not high-acid foods) and how the times came to be, along with the rabbit hole I went down to find this information.  What I say is merely for educational and thought provoking purposes and should be read at your own discretion.  I’m an opinionated little troll.

A very common comment I get on reels and recipes I share, especially if they’re “rebel” canning, meaning untested and uNnApPrOvEd, is that we cannot mimic exactly what commercial processing plants do.  It is parroted by the canning Karen’s and Denise’s over and over and over again in a baseless and unscientific manner.  They hear it from someone else, so it’s definitely true.  BUT when you start looking into it, you’ll understand that we don’t really WANT to mimic those commercial processes but we definitely CAN process exactly what they do in a home environment.  We just have to adjust our processing times.  I think they’d probably croak if they actually read about how our home canning times and processes came to be and how they’re pretty well overprocessed based on scientific studies using completely unattainable levels of food contamination in our homes.  It’s really not that serious and I’m not going to get the botulism because I can something Ball didn’t tell me I was allowed to.  Most of the approved canning recipes come from having something pretty on the shelf that isn’t easy for human stupidity and error to ruin and cause issues and tastes mostly okay.  It has NOTHING to do with any of these sites or groups providing canning recipes testing these “rebel” recipes and finding them to “grow botulism.”  Promise.  And I’ll show you in the coming paragraphs.

But first.

Retort Canning

This explanation is going to be vague and quick because I’m not going into the operational mechanisms of a retort canner, because they are quite different than our home pressure canners, BUT that does not mean we cannot can exactly what they do in our homes.  

There are 5 main types of retort canners, including still, rotary, and agitation.  Rotary means it rotates the food as it heats and agitation shakes the cans or jars as they heat to lead to quicker heating and thermal process during the canning phase.  These retorts heat up VERY quickly and keep the cans from buckling and exploding due to pressure controls, bring the food to the temperature of lethality for around 3 minutes and then can cool them down almost immediately.  They do this by using compressed air in the chamber to keep the cans from buckling, jars from siphoning, and thermal shock breakage to maintain pressure while flooding the chamber with cold water.  This cools the jars in mere minutes as opposed to an hour of cooling time in our pressure canners at home.  

Cans or bags are tested with thermocouples to verify the center of the food reaches the point of lethality (240-250F) during the processing times.  Retorts can cook at a higher temperature using higher pressures which simply means reduced processing times.  In home canning, and even commercial canning, we rely on 3 things: time, temperature, and acidity.  All of these things are taken into account when developing processing times and proving commercial sterility with food.

Retort canners also are able to process hundreds up to several thousands of jars in one go and work very quickly by heating and cooling fast so that massive amounts of product can be processed each day.  What home canner needs to be working and canning that much, that fast?  I mean… when I was picking bushels of green beans every day for weeks this summer, maybe it would have been nice!  LOL

These are the main differences between what a retort canner can do versus what our tiny pressure canners can do at home.  This shows that we can ABSOLUTELY can what they do, our processes just have to be a little different.  Our home pressure canners rely on that cool down time to be used as part of the thermal death time as opposed to the commercial canners using precise times as the thermal death value and then cooling immediately.  Our jars work as thermal batteries to hold heat in as they cool, so most times they get a little hotter as they start cooling.

Commercial Sterility

This means the food processed in a commercial facility has been processed and the end product is free from all microorganisms that cause spoilage and food borne illness without the need for refrigeration.  This is assumed the canned food is stored in normal conditions where they are typically stored, which I assume to be room temperature and away from extreme temperatures (think freezing or burning hot). Ideally 50-75 degrees Fahrenheit.  The process used to achieve commercial sterility take into account heat resistant spores that could possibly survive the process but they will not “grow” in these normal storage conditions.  Basically all times are surrounded around the botulinum kill, which is the temperature and time needed to inactivate the botulism spore.  It is found to be the most thermal resistant one of all and can be very deadly if a spore finds itself in an anaerobic environment (home canned food, store brand cans & foods alike).

Clostridium Botulinum

Since with both commercial canning and home canning, inactivating botulism seems to be the center focus, I’ll add a blurb on that here.  There are three forms of clostridium botulinum, only one of which can cause you harm.  First you have the bacteria, found in soil and in our environment that is completely harmless.  Second, you have the spore, also harmless UNLESS it finds itself in an anaerobic environment.  Then, and only then, can it POTENTIALLY (meaning not ALWAYS) produce the toxin, which is neurotoxic when consumed and can cause severe illness, paralysis, and death.  The good thing is, it’s pretty simple to wash your food to prevent clostridium botulinum from even getting in your jars.  And if you’re still worried after canning, the toxin is EXTREMELY heat sensitive since it’s not got that thick coating a spore has, and can easily be inactivated by boiling for 5-10 minutes.

Thermal Death

After finding the standards for commercial sterility, I came across thermal death.  What the heck does that mean?  I found that commercial sterility uses a thermal death calculation which finds out how long a certain food has to be at a certain temperature to destroy all spoilage and foodborne illness causing microorganisms.  Each cootie that can cause spoiling (and illness) have different thermal death times.  So, they had to find the one with the highest temperature and longest time requirement, which would be clostridium botulinum.  Thermal death involves heating food (in commercial settings) to 240-250F and held at that temperature for certain times.  This requires some math and careful calculations to figure the times and temps needed based on time, temperature, and acidity of each food, along with size and type of container and density of the packing and water content. 

For low acid foods in commercial canning, they have to be proven to have at least a 12-log reduction in clostridium botulinum spores.  This basically means that for every 1 trillion spores, only one can survive.  Yeah, safeguards and processes can be interrupted and done incorrectly, leading to botulism outbreaks, but these processes are pretty airtight keeping any botulinum toxin formation to basically 0.  But, you do occasionally hear of the outbreak, so I’m definitely not claiming store brand canned food is safer.  Cause it ain’t.  

For thermal death to occur, 4 things need to happen:

• protein denaturation
• enzyme inactivation
• cell membrane damage
• DNA damage

These things keep food spoilage and foodborne illness causing microorganisms from surviving and/or reproducing inside those jars or cans, which increase the shelf stability time dramatically in foods, and thus we can consider them commercially sterile.  Keep in mind, commercially sterile is not absolute sterility.  Not everything is inactivated, killed, or denatured in these processes.  But what they can assume is the ones that survive the thermal processing aren’t going to reproduce or reactivate in normal storage conditions (dark, room temperature).

Here’s where the nerd stuff comes into play… feel free to skip.

When calculating thermal death times and figuring out processing times for commercial (and home canned) food, they use different values to depend on the time, temperature, and acidity to make the food commercially sterile.  All of these have been culminated into what is known now as the botulinum cook standard, which is how commercial sterility is reached in commercially canned foods.  There are lots of harmful bacteria that can infect our food, but they use the one that’s the most heat resistant, see also Clostridium botulinum, and that will be your main driver for the calculations.  Also, why it’s called the botulinum cook.

D-Value

D-value is the decimal reduction time.  Yeah, that sounds fancy but it’s simply the time required to destroy 90% of all the spores.  For example, to take a group at one log cycle means to decrease the population of the microorganisms by ten fold.  So, say you have 1,000,000 cooties and you treat them with one D-value, you will then have 100,000 cooties.  There is a different d-value for all microorganisms, including salmonella, listeria, and botulinum.  Doesn’t that sound like a nightmare word problem from grade school.  Definitely should have used apples instead of cooties.

Stay with me here.

Z-Value

The z-value indicates an organism’s thermal death sensitivity to temperature increase.  So, basically as we change the temperature, how quickly does d-value change.  The most common z-value ranges are 5-10 degrees C with clostridium botulinum sitting on top at 10 degrees C.  This means that if they increase the processing temperature by 10 degrees C, they can decrease the processing time by 90%.

F-Value

F-value is the amount of minutes at 250 degrees F (121.1 degrees C) that achieves a specified reduction of spores which produces commercial sterility.  The most common reference is F0 (250 degrees F) with a z-value of 10 degrees C, known as the botulinum cook, with a minimum of 3 minutes for low acid foods.  This ensures the destruction of clostridium botulinum in low acid foods.  You don’t need this for high acid, since botulism does not thrive in an environment with a pH of 4.6 or less.

As I was reading through these values and learning about the math and equations involved along with the thermal death graph of each microorganism that can cause food spoilage or illness, there’s definitive line that tells you at what temperature and what time commercial sterility can occur.  The problem being, at lower temperatures, longer times are required, but commercially that uses tons of energy, precious time, and can render less than desirable products in the end.  Commercially canned food companies want a food you will enjoy eating most of all.  If it’s gross, you’re not going to buy it.  This is why they can use these values and equations to find just how long the food needs to sit at 240-250 degrees F before they can extremely quickly cool it down.  Which is much different than home canning, where we’re slowly heating, hitting that temperature for a certain amount of time, and then SLOWLY cooling, allowing the thermal process to extend into the cooling time because our glass jars act like thermal batteries and hold the heat in far longer than the cans (which was shown and proven in the Bulletin 930 as well because they used both canning jars AND tin cans).  Commercial=less time, high heat, nearly instant cooling period.  Home Canning=more time, lower heat, longer cooling period.  If the z-value tells you anything, it’s that commercial processes can massively increase the temperature to make the f-value much, much quicker.  

Water Bath Processing Low Acid Food:  Where did 240 degrees F come from?!

If you actually read Bulletin 930 from 1946 put out by the USDA, these scientists work in developing and testing different canning times under poor storage conditions and it is absolutely fascinating.  But what you can take from it and the very mathematical equations they used, is that we can rely on time and temperature to ensure our food is processed and safe.  There is no one and done magical processing time that is the only one that works.  This is why when people tout (especially Master Food Preservers) that low acid foods MUST BE pressure canned and brought to 240 degrees F to inactivate botulism and nothing else works, they are extremely inaccurate in their claims, have no scientific thought to their title, and are just regurgitating the things they were told and/or taught.  What you will see in that bulletin is that they PROVED lethality occurs with time and temperature, not temperature alone.  Yeah, pressure canning is faster in some cases, but the audacity to tell folks that water bathing low acid food is unsafe and you’ll get the botulism is an insane take, especially if you’re going to say because ScIeNcE.  Because the science actually proves you wrong on this one.

I’ll get more into that, but first I want to hit on the high points of USDA Bulletin 930, because ya girl read the whole thing and I’m giving you the TL;DR take aways.

USDA Bulletin 930

I started just reading the initial summary of the findings in this white paper and was already throwing things.  The basis of their science was to can jars that had not been inoculated and then inoculate jars with large amounts of microorganisms.  This is the same methods as is used in commercial canning technique development.  They did immediately acknowledge that basing home canning times off of the same calculations of that of commercial canning were leading to very overprocessed and unpalatable food because no one had taken into account the extended cooling period our home canners have, in which the thermal process continues to occur.  Our glass canning jars actually insulate the food more than the cans used commercially that cool way more rapidly…. which I think is extremely important to note.  The canning times for home canners were arbitrarily derived from those that were used commercially leading to failures for those trying to can at home, and not really because of botulism, but because the food they were preserving was gross and they were frustrated.  People wanted help because their food was really gross and these guys set out to pave the way to trying to understand clostridium botulinum in home canning (especially since prior to this there were some pretty gnarly commercial outbreaks and deaths… looking at you California black olives) and to help folks out.  There were sporadically about 10-12 cases of botulism every year attributed to home canning and the cases were described as carelessness and faulty technique.  They didn’t do this because half the population died of botulism canning in their homes; they did it because the food was GROSS.  What happened in the end was they overshot temperatures and times for processing due to an anticipated margin of error in home canning and for an extreme measure of safety.  Then the USDA and NCHFP took hold of this, said GOOD ENOUGH, and came up with the rule that 240F or you die of botulism.  Which isn’t even close to what they said in this bulletin.

Let’s get into it!

The Technique

Processing times were computed according to heat penetration data of certain meats and vegetables they had.  They also considered the heat resistance data they had on Cameron’s putrefactive anaerobe number 3679.  What’s that you ask?  Oh, it’s an anaerobe that was originally isolated from a can of spoiled corn that was described as “morphologically similar” to Clostridium botulinum but also “probably not identical.”  These spores are more heat resistant than Clostridium botulinum… almost twice as much.  READ THAT AGAIN.  The anaerobe they used to test the botulinum cook or kill (z-value) was just shy of twice as heat resistant as compared to Clostridium botulinum.  So this entire bulletin and study was based on ensuring the time and temperature rendered no active number 3679 in any jars. And to top it off, they actually don’t really understand what this anaerobe is at all but it does not produce a toxin that harms humans; it just rapidly reproduces in an anerobic environment and farts so much your jar seal fails.  So, I guess I understand why they opted to use the “similar guy” as opposed to playing around with botulinum… that would make me uneasy too.  But, also, OVERBOARD much as this PA 3679 very far exceeds any heat resistance we will see from C. botulinum.

Just to give you some numerical visuals of of comparisons between PA 3679 and Clostridium botulinum, the D-value for asparagus for: 

• PA 3679 0.515
• C. botulinum 0.05

For milk, the D-value is:

• PA 3679 1.29
• C. botulinum 0.07

Canning times were calculated by relating time and temperature on the thermal death curve.  They were plotted according to a logarithmic scale by using the time required in minutes to destroy the organism against the temperature required on a linear scale.  The lethal rate was found by the ratio of time in minutes required to destroy, in this case, C. botulinum at 250F to time required to destroy at any other given temperature.  This plotted curve SHOWS that water bath canning and thermal lethality is absolutely possible.  Z-values are low at 200F but increase very rapidly once they approach 250F, but it doesn’t mean there’s no lethality at 200F.  You just need more time at that temperature.  These calculations were made by very simple equations and it was fascinating to look at the graphs and their work.  I know I sound very critical of this study, but it isn’t as much the bulletin and the information they gave, so much as how the USDA and NCHFP cherry picked some of the information without telling the whole truth and ran with it, leaving people to blindly sheep and believe things and think that everything else will cause instantaneous death outside of their recommendations.  That’s all.  Oh yeah, the NCHFP (your home food preservation website) that provides you with research-tested recipes did NONE of the work themselves.  The NCHFP was formed to simply distribute data and recipes already tested and collected, not do a dang thing past that.  In all honesty, this bulletin was groundbreaking and amazing work, aside from the overshot safety measures they gave, but I can’t say I blame them.  You want the safest product and the safest method and you gotta assume everyone is dirty and stupid.  I get it.

They compared shorter processing times and found that they were subject to more margin of error when applied to the lethality curve and then transposed on the cooling curve.  (I you don’t understand any of this, I’d recommend reading the bulletin and studying the graphics they gave, they’re fascinating!)  The area between these two curves was measured and used to calculate the margin of safety.  On these curves, it found that the home canned food in jars remains constant and sometimes even increases before cooling and after the processing time is complete.  This period had never been accounted for prior, which was leading to very overprocessed food.  Since this wasn’t a thing, people tended to err on the side of longer processing times to give themselves a greater margin of safety.

All these “tested” recipes are run through these curves and equations to ensure safety.  I am quite certain that Mr. Ball and others are not inoculating each and every jar of new recipes they come up with in recent years to ensure your safety.  No.  They’re running them through ole Mr. Ball’s equations and calling it good based on calculated density and acidity.  When I see people post about using only tested recipes because they were tested by inoculation in a lab, my eyes roll right on out of my head.  YOU KNOW for a fact they’re not testing any high acid foods, and I guaran-dang-tee they’re basing their times and safety off these very equations and curves and graphs according to known densities of ingredients and calling it a safe recipe.

Methodology

To get these numbers, they obtained heat penetration data on quite a few different ingredients, like pork, beef, chicken, asparagus, lima beans, snap beans, beets, carrots, corn, okra, peas, pumpkin, spinach, summer squash, and sweet potatoes.  They were in various jar sizes of pints and quarts and also tin cans.  All preparation and packing of jars and cans was done as close as possible to what processing methods would be done at home.  They didn’t want everything lab sterile, but just clean for best results of this study.  All ingredients were hot packed, meaning they were heated and pre-cooked prior to filling jars and cans.  Thermocouples were used and placed in the calculated center of the food that is considered the slowest to heat.  Anything that was raw pack was placed in hot water of 170 degrees F prior to canning until the center of the food read 170F.  This just ensured everything was exactly the same to get rid of that variable of start temperature.  Hot pack jars went straight into the canner.  Thermocouples were also placed in jars that were in the center of the canner and on a couple sides in different layers inside the pressure canner.  Once the canner hit 212F, they let it exhaust steam for 10 minutes before adding the weight.  After adding the weight, they started the processing time and the time from start to when the center of the food reached 240F was documented.  The canner was then cooled to precisely 212F and jars were removed to cool.  From this, heat penetration data was obtained for each ingredients.

Inoculation

The the inoculated packs began.  First up, chunked pork.  Wire bail jars with a glass lid and a rubber gasket were used in testing.  Pints of vegetables were canned with metal closures.  The results of these inoculation experiments were applied to meats and vegetables in other sizes of jars and types of jars as well.  PA 3679 (that we talked about earlier) was used as the inoculant.  It was, and maybe is, widely used by canning labs as the test organism to show C. boutlinum cook.  Remember, at 250 degrees F, this anaerobe shows heat resistance of just less than twice that of C. botulinum’s resistance in identical situations.  The only thing these two different clostridiums have in common is a similar slope on the thermal-death-time curve.  PA 3679 grows very rapidly in meats and vegetables that have been canned, as it’s anaerobic, and will rapidly give off gas production, causing a bulging lid or failed seal pretty quickly.  One thing they did do was to make sure to kill off any vegetative cells of PA 3679 prior to canning and then verify the heat resistance of the spores, which is the same thing some are concerned about with C. botulinum… those spores “waking up” inside our jars and producing the toxin.  

Jars of meat in quarts were inoculated with approximately 30,000 spores of PA 3679 and jars of vegetables in pints were inoculated with 10,000 spores.  A needle was used to inject these spores into the very center of the food (the slowest and last to heat).  They made “packs” with each ingredient with at least 24 inoculated jars and 12 control jars (un-adulterated).  

Process for Meats

The previous processing times for pork was 120 minutes at 250F (the USDA recommended process time) which was reduced to 80 minutes at 250F.  Further testing in this bulletin led to reducing the process temperature to 240F now that they took into account the cooling period.  Jars of meat were inoculated and controls were kept as well in packs as mentioned above and were processed for 60, 80, 90, and 100 minutes respectively.  After processing and verifying the jars had a good seal, they were then stored in horrible conditions and actually incubated at 98.6 degrees F for 90 days, checking daily for spoilage. 

The results?  All spoilage of inoculated jars occurred at 60 and 80 minutes, but no inoculated jars processed for 90 and 100 minutes spoiled.  All spoilage occurred within 1 month of processing and none occurred after in the additional year and a half of incubation.  It is important to note that no control jars spoiled.

​Process for Vegetables

From there, they calculated times for different vegetables based on an algebraic equation that was then graphed to find the intersection.  A vertical line was also added at 2.6 times the standard to show the lower limit of error (to account for margin of error).  This is called the line of regression and the regression equation is as follows:

yr (process value) = a (constant vertically) + b (slope of the line)x

yr=a+bx

x=processing time

Again, in the testing of vegetables in pint jars, no control jars spoiled, even in asparagus that was processed for as little as 7 minutes.  Processing times were calculated from these findings and rounded up to the nearest 5 or 10.

​Takeaways and Findings

In their discussion they said that these processes are fine for home canned foods as long as every particle of food has been raised to a lethal temperature and held for a sufficient length of time to kill the most resistant spoilage organism present.  In this case, thousands of times more spores than anything we would naturally come in to contact with in our kitchens and an organism just short of 2 times the heat resistance as Clostridium botulinum.  Nothing about water bathing low acid foods is illegal or will cause you to die.  Nothing.  Just… time and temperature and you’ll be fine along with properly heating your food prior to consumption.  But also, we are massively overprocessing our food in the name of safety when the existence of their testing is unnatural and lab manipulated.  We will NEVER come into contact with that much botulism in the very center of our jars in our lives.  And yet, meat times are 90 minutes for quart jars, when the control jars grew nothing even at 60 minutes.  I honestly wonder what the “real” times could be.

I understand why though.  They wanted to create the best and safest techniques and it makes sense. Fool proof.  Err toward processing times longer than needed for safety.  Using the lowest value is a possibility, but they calculated too much variable and unknown with those.  But the best thing they did here was prove that the thermal process and thermal death can be calculated and is not just a 240 degrees F internal temperature and done.  

My favorite part?  In the discussion they wrote we have good reason to believe PA no. 3679 definitely had greater resistance than anything commonly encountered by home canners.  The number of spores was in great excess to the normally expected natural load.  BUT they did this along with the center placement to ensure maximum probability of survival to ensure they could definitively give a safe recommendation.  Many of the old times from the USDA were adjusted and home canning is now what it is today.  There’s really been nothing done since except a few studies here and there checking out the atmospheric steam canning and showing water bath canning low acid food is fine (although none of those studies have been picked up by the NCHFP and will never be).

What do we take from this?

You can choose that.  I found it fascinating to see actually where our times for canning came from and how they tested and adjusted them.  The work they did on bulletin 930 was seriously so cool and so interesting.  I think if we can take anything, it’s that our food is very much overprocessed in the name of safety so quit being afraid of your jars of food; the finished product ain’t gonna unalive you.. they made sure of that.  But also, maybe these folks being critical of people that don’t can exactly the way they do could not be as supported as they are.  So many people think it’s tested or the highway, and that just isn’t so.  We can can anything they can commercially; it’s not that their equipment is superior to ours, it’s that it’s different than ours.  I don’t have any need for canning 20,000 jars in one day and commercially, using my tiny All American would put them out of business in a hurry.  Different doesn’t mean you die.  

Take this as encouragement, drop the fear of botulism, and start canning.  Use a pressure canner, a water bath canner, a steam canner, I DON’T CARE.  Just be smart about food safety and trust the process.  And if you’re worried, boil your food for 5-10 minutes prior to consuming.  That’s all it takes.  The home canning process isn’t hard!  Don’t make it that way either!  Home canning allows you to eat food you raised or grew that you know is the best quality unlike the trash they sell you at the store.  Think 3D printed meat from a certain soup company…..  And if you don’t grow your own foods, support a farmer that grows their own fresh produce and keep our money and health out of the pockets and hands of big corporations… commercial products can have botulism in them too.

Happy canning!

Links & References for Further Reading

https://www.nal.usda.gov/exhibits/ipd/canning/items/show/85

https://canningdiva.com/the-240-myth-botulism-heat-resistance-and-the-misunderstood-pressure-only-mandate/: Commercial Canning and How It Shaped Home Canning Practices https://agriculture.institute/food-microbiology-cpo/understanding-commercial-sterility-food-products/: Commercial Canning and How It Shaped Home Canning Practices https://www.afdo.org/resources/canning-laws-and-guidance/: Commercial Canning and How It Shaped Home Canning Practices https://canningdiva.com/wp-content/uploads/2025/06/2025.06.27-01.33-canningdiva-685df4d495585.pdf: Commercial Canning and How It Shaped Home Canning Practices https://www.retorts.com/white-papers/commercial-sterilization-defined/: Commercial Canning and How It Shaped Home Canning Practices https://pmc.ncbi.nlm.nih.gov/articles/PMC10916645/: Commercial Canning and How It Shaped Home Canning Practices https://www.meatsandsausages.com/canning-equipment/canners-pressure-retorts: Commercial Canning and How It Shaped Home Canning Practices