I cannot find any explanation how the USDA derived the processing times for various pressure canning recopies.
My guess is they used a thermometer in middle of jar of food being tested to obtain a time value sufficient for temperature to reach above certain value for certain period.
Why are some processing times for some foods are 20 minutes while others over 1 hour. Is this entirely due to different rates of heat transfer ?

Regards,

Adam

Adam Seychell wrote:
> I cannot find any explanation how the USDA derived the processing times for various pressure canning recopies.
> My guess is they used a thermometer in middle of jar of food being tested to obtain a time value sufficient for temperature to reach above certain value for certain period.
> Why are some processing times for some foods are 20 minutes while others over 1 hour. Is this entirely due to different rates of heat transfer ?

can you give examples?

my guess is that it is a combination of factors
including acidity, the possibility of air gaps,
initial estimates of contamination chances, and
as you say heat transfer differences.


songbird

On 3/12/2017 7:30 AM, songbird wrote:
> Adam Seychell wrote:
>> I cannot find any explanation how the USDA derived the processing times for various pressure canning recopies.
>> My guess is they used a thermometer in middle of jar of food being tested to obtain a time value sufficient for temperature to reach above certain value for certain period.
>> Why are some processing times for some foods are 20 minutes while others over 1 hour. Is this entirely due to different rates of heat transfer ?
>
> can you give examples?
>
> my guess is that it is a combination of factors
> including acidity, the possibility of air gaps,
> initial estimates of contamination chances, and
> as you say heat transfer differences.
>
>
> songbird
>
Then there is the "mass" problem, some canned foods are thicker and
heavier, therefore more time is needed. Most of the things you need to
know are on the web, especially in the USDA files.

I'm old enough to remember when lots of home canned foods went bad
quickly because the person canning the food didn't use pressure canners
but just boiled the heck out of the canned food. Botulism is not your
friend.

We lost power around 10pm last night and just got it back around 8am
this morning. Overloaded electric substation, goes out frequently here.
It's nice to get heat again.

George

On Sunday, March 12, 2017 at 11:36:55 PM UTC+11, songbird wrote:
> Adam Seychell wrote:
> > I cannot find any explanation how the USDA derived the processing times for various pressure canning recopies.
> > My guess is they used a thermometer in middle of jar of food being tested to obtain a time value sufficient for temperature to reach above certain value for certain period.
> > Why are some processing times for some foods are 20 minutes while others over 1 hour. Is this entirely due to different rates of heat transfer ?
>
> can you give examples?
>
> my guess is that it is a combination of factors
> including acidity, the possibility of air gaps,
> initial estimates of contamination chances, and
> as you say heat transfer differences.
>
>
> songbird

I since found few articles with a more technical explaining of the methods.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4304559/
http://www.fao.org/docrep/010/ai407e/AI407E22.htm

It seems they are primarily interested in the "cold spot" during processing.. But as you say the acidity would be factor too. I was comparing processing times in the USDA home canning guide , and I generally see pattern of thicker low acid foods have significantly longer processing times. One contradicting bit of information in the Canning Guide is processing times for "Spinach and other greens" is 70 minutes, yet "BEANS, SNAP AND ITALIAN€”PIECES" is 20 minutes. Both are greens. Would this be due to poor convection heating inside a jar packed with leaves ?.

I just bought a pressure canner ignorant of the process. Thinking I could pressure can all my favorite meals and just have them there ready to grab when I am hungry. Man, I had no idea what I was up for and what I needed to learn. I found out the hard way why nobody pressure cans broccoli. No regrets, and looking forward to having my first home canned meal.

On Sun, 12 Mar 2017 10:04:40 -0500, George Shirley >
wrote:

> Botulism is not your
> friend.

Which is why Mom always boiled home-canned vegetables for fifteen
minutes, stirring to make sure all parts contacted oxygen.

I suspect that the researchers found "instant destruction on contact
with 100C oxygen, tell 'em to boil it five minutes to be sure." Then
the book writers said "five minutes will do it, tell 'em ten minutes
to be sure everybody does it for five". And Mom read "ten minutes"
and decided she'd better do it fifteen to be sure it got the full ten.

No wonder I didn't like green beans.

--
Joy Beeson
joy beeson at comcast dot net
http://wlweather.net/PAGEJOY/

On 3/13/2017 10:50 AM, Joy Beeson wrote:
> On Sun, 12 Mar 2017 10:04:40 -0500, George Shirley >
> wrote:
>
>> Botulism is not your
>> friend.
>
> Which is why Mom always boiled home-canned vegetables for fifteen
> minutes, stirring to make sure all parts contacted oxygen.
>
> I suspect that the researchers found "instant destruction on contact
> with 100C oxygen, tell 'em to boil it five minutes to be sure." Then
> the book writers said "five minutes will do it, tell 'em ten minutes
> to be sure everybody does it for five". And Mom read "ten minutes"
> and decided she'd better do it fifteen to be sure it got the full ten.
>
> No wonder I didn't like green beans.
>
The beans must have been cooked to mush with the fifteen minute boil and
stir and then the time in the pressure canner.

Our pressure canner was purchased in the mid-sixties and, with good
cleaning and new gaskets is till going strong. Thank you Sears and
Roebuck. <G>

George

Adam Seychell wrote:
> songbird wrote:
>> Adam Seychell wrote:

>> > I cannot find any explanation how the USDA derived the processing times for various pressure canning recopies.
>> > My guess is they used a thermometer in middle of jar of food being tested to obtain a time value sufficient for temperature to reach above certain value for certain period.
>> > Why are some processing times for some foods are 20 minutes while others over 1 hour. Is this entirely due to different rates of heat transfer ?
>>
>> can you give examples?
>>
>> my guess is that it is a combination of factors
>> including acidity, the possibility of air gaps,
>> initial estimates of contamination chances, and
>> as you say heat transfer differences.
>>
>>
>> songbird
>
> I since found few articles with a more technical explaining of the methods.
> https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4304559/
> http://www.fao.org/docrep/010/ai407e/AI407E22.htm
>
> It seems they are primarily interested in the "cold spot" during processing. But as you say the acidity would be factor too. I was comparing processing times in the USDA home canning guide , and I generally see pattern of thicker low acid foods have significantly longer processing times. One contradicting bit of information in the Canning Guide is processing times for "Spinach and other greens" is 70 minutes, yet "BEANS, SNAP AND ITALIAN€”PIECES" is 20 minutes. Both are greens. Would this be due to poor convection heating inside a jar packed with leaves ?.

yes. air bubbles and the huge surface area that is
possibly contaminated. leaves are very much open to
the air over both surfaces plus inside the leaf itself.
remember what leaves are, the reason they exist...
a bean pod in comparison is vastly more compact with
much less surface area and that makes it a lot less of
a contamination risk. not that it is zero, but much
less.

when it comes down to leafy greens i'll eat them fresh
or freshly steamed. i've never canned/processed any of
them for storage. beans i also eat fairly fresh or
lightly steamed. i don't like them cooked to mush.

have you considered drying them instead? dehydrated
kale is very popular these days and i like that texture
much more than mush. i'm not sure spinach would fare well
under such treatment.

the other thing to consider is just making sure there
is enough acid in there (pickled and sweet and sour) and
then you are much safer. i don't do pressure canning here.
nothing i want to put up is low acid nor would i want to
do low acid. botulism just isn't something i ever wish
to experience. like mushroom toxins the margin of error
is very low.


> I just bought a pressure canner ignorant of the process. Thinking I could pressure can all my favorite meals and just have them there ready to grab when I am hungry. Man, I had no idea what I was up for and what I needed to learn. I found out the hard way why nobody pressure cans broccoli. No regrets, and looking forward to having my first home canned meal.




songbird

On 3/13/2017 1:59 PM, songbird wrote:
> Adam Seychell wrote:
>> songbird wrote:
>>> Adam Seychell wrote:
>
>>>> I cannot find any explanation how the USDA derived the processing times for various pressure canning recopies.
>>>> My guess is they used a thermometer in middle of jar of food being tested to obtain a time value sufficient for temperature to reach above certain value for certain period.
>>>> Why are some processing times for some foods are 20 minutes while others over 1 hour. Is this entirely due to different rates of heat transfer ?
>>>
>>> can you give examples?
>>>
>>> my guess is that it is a combination of factors
>>> including acidity, the possibility of air gaps,
>>> initial estimates of contamination chances, and
>>> as you say heat transfer differences.
>>>
>>>
>>> songbird
>>
>> I since found few articles with a more technical explaining of the methods.
>> https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4304559/
>> http://www.fao.org/docrep/010/ai407e/AI407E22.htm
>>
>> It seems they are primarily interested in the "cold spot" during processing. But as you say the acidity would be factor too. I was comparing processing times in the USDA home canning guide , and I generally see pattern of thicker low acid foods have significantly longer processing times. One contradicting bit of information in the Canning Guide is processing times for "Spinach and other greens" is 70 minutes, yet "BEANS, SNAP AND ITALIAN€”PIECES" is 20 minutes. Both are greens. Would this be due to poor convection heating inside a jar packed with leaves ?.
>
> yes. air bubbles and the huge surface area that is
> possibly contaminated. leaves are very much open to
> the air over both surfaces plus inside the leaf itself.
> remember what leaves are, the reason they exist...
> a bean pod in comparison is vastly more compact with
> much less surface area and that makes it a lot less of
> a contamination risk. not that it is zero, but much
> less.
>
> when it comes down to leafy greens i'll eat them fresh
> or freshly steamed. i've never canned/processed any of
> them for storage. beans i also eat fairly fresh or
> lightly steamed. i don't like them cooked to mush.
>
> have you considered drying them instead? dehydrated
> kale is very popular these days and i like that texture
> much more than mush. i'm not sure spinach would fare well
> under such treatment.
>
> the other thing to consider is just making sure there
> is enough acid in there (pickled and sweet and sour) and
> then you are much safer. i don't do pressure canning here.
> nothing i want to put up is low acid nor would i want to
> do low acid. botulism just isn't something i ever wish
> to experience. like mushroom toxins the margin of error
> is very low.
>
>
>> I just bought a pressure canner ignorant of the process. Thinking I could pressure can all my favorite meals and just have them there ready to grab when I am hungry. Man, I had no idea what I was up for and what I needed to learn. I found out the hard way why nobody pressure cans broccoli. No regrets, and looking forward to having my first home canned meal.
>
>
>
>
> songbird
>
I find it more convenient to semi-cook greens and then vacuum bag and
freeze. Have held them two or three years in the freezer and they're
still good.

George

On Mon, 13 Mar 2017 12:37:24 -0500, George Shirley >
wrote:

> The beans must have been cooked to mush with the fifteen minute boil and
> stir and then the time in the pressure canner.

The fifteen-minute boil was after you *open* the cans, in case there
is toxin in them.

All cooking before canning ever does is make more stuff fit into the
can.

--
Joy Beeson
joy beeson at comcast dot net
http://wlweather.net/PAGEJOY/

On 3/13/2017 8:30 PM, Joy Beeson wrote:
> On Mon, 13 Mar 2017 12:37:24 -0500, George Shirley >
> wrote:
>
>> The beans must have been cooked to mush with the fifteen minute boil and
>> stir and then the time in the pressure canner.
>
> The fifteen-minute boil was after you *open* the cans, in case there
> is toxin in them.
>
> All cooking before canning ever does is make more stuff fit into the
> can.
>
I've never had a problem with pressure canned jars going bad unless a
lid wasn't put on properly. How, exactly, can a properly canned jar get
toxin in it?