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Head space question

 
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I hate it when someone says "Always cut that board to exactly 12 inches".   Well, as an engineer I'd say it's nearly impossible to make them exactly 12".  It's much better to say 12 inches plus or minus 1/16th".  Or at least 12" but no more than 12.25".

So head space is annoying.  Often it's 1/4".  So is that a minimum head space, a maximum head space or is it that if you're even a hair off, you'll die?  If I'm making pickles and I have enough to fill the last jar 90% and leave a big head space, is that a jar of death or is it just wasted space that more pickles could've fit into?

Inquiring minds want to know...

Edit: I'm talking about water and pressure canning
 
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minimizing headspace is minimizing oxygen. i think there’s a fair bit of wiggle room, but generally the less oxygen, the longer-keeping. in your example, i’d just use that jar first, no worries.
 
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This is where following the direction can help.

Headspace is allowing room for expansion of solids or bubbling-up of liquids. If the foods get on the seal they can ruin the seal.

Different foods react differently.

Peas and beans might swell which is different from how a fruit preserve would react.  And the same with something with a lot of liquid.

Since I always follow the directions I can never remember how much headspace or headroom for I use.  So I use the manual or the recipe.
 
Mike Haasl
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I suspect that for some foods the headspace is a minimum for a particular reason.  And for others it's a maximum for different reasons.  But that's just my suspicion.  
 
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I have a jar of sauerkraut with a bulging metal lid even though I’m burping it twice a day. I left half an inch but the pressure in lower layers has pushed the glass weight against the underside of the lid.

As an engineer / scientist, then why not set up multiple jars with different headspace as the only variable and see what happens?
 
Mike Haasl
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Because the test for success would be if I get sick or not

I'm pretty sure they'll seal, I'm more worried about safety...
 
Anne Miller
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Are we talking about fermenting or canning?  Did I miss something?

Mike said, " If I'm making pickles and I have enough to fill the last jar 90% and leave a big head space, is that a jar of death or is it just wasted space that more pickles could've fit into?



When canning too much headspace can cause a weak seal.  

Maybe add more liquid? If the jar seals, I feel you are okay.  If it doesn't seal put it in the fridge and enjoy.
 
Mike Haasl
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Sorry, I was talking water bath and pressure canning...

Anne, do you know why that is?  In my mind, hot food and hot air in the jar both shrink when they cool.  Air shrinks a lot as it cools, food perhaps not as much.  So I'm not sure why more head space (more air) in the jar would lead to weaker seals.  But I don't really know.
 
Edward Norton
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Mike Haasl wrote:Because the test for success would be if I get sick or not
I'm pretty sure they'll seal, I'm more worried about safety...



Good point and I wouldn’t want you to get sick. I use a basic ‘look, sniff, sample’ test for fermented stuff.

On the subject of exactness and seeing as you’re an American - how do you feel about recipes that require cups, especially in baking where exactness is often a requirement to success? As a Brit who cooks, I can work with both metric and imperial (freedom units?) preferring the former. But cups drive me nuts.
 
Mike Haasl
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Cups usually refer to measuring cups which are fairly consistent.  No issue for me.

It's just that hitting 1/4" head space is a pretty precise target.  If I knew that 1/2" to 1/4" was actually fine it would make things much easier...
 
Edward Norton
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I guess it helps when you grow your own food. I’m still writing shopping lists, so when I see a recipe that says four cups of chopped tomatoes, I have no idea how to buy the required amount of tomatoes. I have to start searching on the internet and wade through the spam sites before finding out the weight.

I just checked one of my recipe books on canning - it says leave 15mm gap. There’s your wiggle room.
 
Anne Miller
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Mike Haasl wrote:Sorry, I was talking water bath and pressure canning...

Anne, do you know why that is?  In my mind, hot food and hot air in the jar both shrink when they cool.  Air shrinks a lot as it cools, food perhaps not as much.  So I'm not sure why more head space (more air) in the jar would lead to weaker seals.  But I don't really know.



This is when the jars are in the water bath or the pressure canner and why sometimes people talk about food liquids coming out during the canning process.

The air in the jar needs to be forced out during the canning process so the jars will create a good seal, a vacuum.  Too much air can also cause discoloration of the food.

This has nothing to do with the cooling process unless there is a loose seal causing the jars to not seal.
 
Mike Haasl
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As I understand it, some air is pushed out of the jars when they boil in the canner (or get hotter in the pressure canner), but there is still air in there.  When the jars come out of the canner, the lids aren't sucked down yet since the contents (food and air) are hot.  As the contents cool, they shrink which causes the vacuum and makes the lids suck down.  

If that's correct, that's why I'm thinking a bit more air wouldn't hurt from a sealing point of view.  Discoloration could still be a very valid reason to not exceed the head space.
 
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Another engineer weighs in on the question.   As for the vacuum.  The is no guarantee that all of the air will be pushed out by the stream created in the headspace but most of it should be.  

As the fluids cool, so do the gases.  Ultimately the gases will condense back into a liquid.  The ultimate vacuum or gas pressure will be governed by the temperature and vapor pressure of the liquid (basically water with salts) and the amount of residual air (nitrogen 80% and oxygen 20%).  These are approximate numbers of course.  

I would imagine that a large headspace would have a reduced vacuum because percentage wise there is much more residual air in the jar.

Hope this helps rather than confuses.
 
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Canning is a combination of chemistry and physics. The chemistry of any given recipe can change the physics of the headspace. Anne 100% has the right of it. Follow each recipe, and yup - measure it. There are canning funnels with the various measurements conveniently marked on the bottom edge, with a cutout, so you don't have to guess or try to stick a mini ruler in there. Too much headspace, and you risk oxidation spilling the whole thing, even if you get a great seal. Too little headspace, and you run the risk, as Anne said, of bubble up, seepage, and even exploded jars - all of which risk all your efforts and sometimes, your life. So, especially when you're first learning, it's wisest to use well trusted recipe sources, and follow them closely especially the headspace recommendations.

Once you get a strong grasp of it all, and which foods do what, you can often change them a bit, playing with spices, sweetness, etc. But, that, imho, is not a good idea for beginners.

(I have this one: https://www.williams-sonoma.com/products/progressive-funnel/?catalogId=79&sku=9607698&cm_ven=PLA&cm_cat=Google&cm_pla=Outdoor%20%3E%20Canning%20%26%20Preserving&adlclid=766c45bae2be14d5f3ef24c625ee9926&msclkid=766c45bae2be14d5f3ef24c625ee9926)
 
Anne Miller
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Thanks, Carla for the explanation.

I understand chemistry as it was a favorite subject.

I think Mike wants the physics part of the equation and the problem is I never took physics and can't explain that part of the equation.

Mike's question was a good example of something I bet most canners would like to know.
 
Mike Haasl
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Thanks for the added information Carla!  I guess I just figure there is likely a range of head spaces that are ok.  Like when it says 1/4" it really means that 3/16 to 5/16 is actually ok.  It would just be nice to know that.  Or if when they say 1/4" they really mean 1/4 to 3/8".  

I do measure with step edged stick so it's easy to get it very close.  I'm just not sure how close is close enough.  The missus has been known to take about a quarter teaspoon of soup out of a pint jar to get the head space right.  Is that being overly nitpickey?  Does a 1" head space need to be exactly 1" or is a mm high or low ok?  Or 2 mm?   Sorry for the metric units but I didn't want to leave anyone out...
 
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Mike Haasl wrote:The missus has been known to take about a quarter teaspoon of soup out of a pint jar to get the head space right.  Is that being overly nitpickey?  Does a 1" head space need to be exactly 1" or is a mm high or low ok?  Or 2 mm?   Sorry for the metric units but I didn't want to leave anyone out...



I don't think I've ever gotten *quite* that picky. I've removed or added a teaspoon, or so, because I have previously had seepage, and I've had stuff get funky from oxidation, and once, even discovered mold, because of too much headspace. I'd run just a tad short of enough to fill the last jar, and thought, "oh, it's only about an 1/8th of an inch...". So, while I'd go 1/16" (a millimeter or two), I personally would not feel comfortable with much more variance than that. I've done less canning, in the last 20yrs, than I had, in the 20, before that, but still do a fair share, each year, and that number is picking up, again, so I only recently bought that funnel, too make it easier to get it right.

Anne, I thought your explanation was great! Honestly, I love this thread, and think everyone has brought a lot to the table! Thank you, Ed & Ralph! Mike, this is definitely asomething we all need to be mindful of, and something most people don't really understand, especially when they're just starting out!
 
Anne Miller
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Something I thought of while reading Carla's reply is that any air bubbles that are not removed will add headspace.

Experience canners may know this though in case someone who is newer at this may not.

What I have found is one of the best tools to remove air bubbles is a chopstick, as in Chinese food.
 
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A chopstick is one of my wife's favorite canning tools also and she's does it often.  Cans that is.  All kinds of foods, water bath and pressure.

He comment the other day was that she has never had a seal fail with water bath canning but routinely has a 5% or so failure rate with pressure canning.  A nother interesting statistic is that the smaller single level (for quarts at least) canner we have never has a jar crack.  On the larger double level canner which holds 14 or perhaps 16 what jars we have had several jars crack which is so disheartening.

As she said even after all these years I am still learning.
 
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I'm not an expert, and I don't have any hard facts, but every pressure canning recipe I've ever used calls for 1" headspace.  I think a major factor in headspace guidelines is how much bubbling is expected in the jar while it's being processed--pressure canned jars bubble violently, sometimes for an hour or two after coming out of the canner.  Jams and jellies don't really do much of that, so less space is needed to accommodate the bubbling.

As for the scenario of last jar, not enough liquid, it might make the food unsafe (especially in pressure canning).  Air is an insulator and food surrounded by air won't get as hot as food surrounded by liquid, so the harmful stuff might not be destroyed on foods not submerged in liquid.  It'll probably be okay, but there's still a chance it might not be.

I'm not super exacting with headspace.  I eyeball it using the threading of the jars.  I can be off by 1/8" sometimes and it's never been a problem.  My jellies sometimes end up having almost 1/2" headspace because I'm a messy canner and I don't want to miss anything I might have slopped on the rim.  Ensuring the seal is more important to me than the possibility of a little extra oxidation.  Sometimes I'll can half-jars of jellies and jams and just use them first, within a couple months.  I haven't had any issues with that so far (knock wood), but they're high acid foods with lots of sugar, so not as dangerous as like, green beans or meat.
 
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S Tonin wrote:

As for the scenario of last jar, not enough liquid, it might make the food unsafe (especially in pressure canning).  Air is an insulator and food surrounded by air won't get as hot as food surrounded by liquid, so the harmful stuff might not be destroyed on foods not submerged in liquid.  It'll probably be okay, but there's still a chance it might not be.



Air is not an insulator in all circumstances.  When it is confined to a small space and is not subject to convection currents and is dry, yes it is a decent insulator.  However when it is in the presence of superheated steam and violently bubbling liquid it does not insulate.  That said the heat transfer rate is significantly less than liquid.  This is why you can survive for a long time at below freezing temperatures outside even with little clothing but will die of hypo thermia in 10 +/-  minutes in 40 degree water.  My suspicion is that if it is in the canner for the specified period of time there is little risk of survival of the nasties in the drier part of the jar.
 
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Edward Norton wrote:I have a jar of sauerkraut with a bulging metal lid even though I’m burping it twice a day. I left half an inch but the pressure in lower layers has pushed the glass weight against the underside of the lid.

As an engineer / scientist, then why not set up multiple jars with different headspace as the only variable and see what happens?


For sauerkraut, and other lactic acid fermentations, it doesn't matter. The only thing that's important is: the solid stuff has to stay under the liquid. That's why it has something on it to press it down. But if the kraut and the liquid fill only half the jar (or even less), that isn't a problem.
This is totally different with 'canned' stuff (we here call it 'wecked', because we use the jars of the Weck brand)
 
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