Liquid Loss in Jars When Canning: Siphoning Explained

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An extremely common message I get on social media is pictures of jars that have a lower level of liquid after canning than they did before. Plus a picture of the canner with some of the food or liquid in the bottom. What did I do wrong? Is the food still safe to eat? Can I store it? Do I need to reprocess it?

I’m going to take all these questions that may be swirling around in your mind as someone new to home food preservation and canning, explain what happened, how to prevent it, or just roll with it and go. Liquid loss in jars isn’t the end of the world, and here’s why.

Liquid loss in jars after canning is also known as siphoning. At the end of the day, siphoning is not a big deal if your jars still seal and have half of the liquid. If they lose more than that, I would assume there was some major error in your part and you should probably just pop that jar in the fridge and eat it soon.

Siphoning is a very normal and frequent occurrence that can happen to anyone. It is basically caused by rapid heating or cooling and the expansion of the jar contents leads to leaking out of the jar from too quick of pressure and temperature changes. Normally the expansion is when air escapes from the jar, but if you’re heating too violently, then you’re making the food come out, too! That’s the simple version of it and if you’d like to scientific answer to that, by all means do your research because I’m not going there. I really just want to show you how to troubleshoot what may be causing it and give you some possible solutions.

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Siphoning generally has 4 main causes:

Too rapid heating phase
Too rapid cool down time
Tightly overpacked jars
Not enough headspace

Too Rapid Heating Phase

This is the booger that gets you if you raw pack or cold pack. If you add your food contents to your jar cold or at room temperature and then heat up your pressure canner at full tilt rocket fuel, you’re obviously going to get some siphoning because the water outside the jars is heating up a whole bunch faster than the inside of the jars. Things get angry and complain when you do that, and if you didn’t bust any jars, you will absolutely have siphoning. I run into this when I cold pack food and use my electric pressure canner. I can’t tell the electric pressure canner to heat the jars a bit slower than normal since it has one singular setting, so I usually have a little bit of siphoning from doing this. To mitigate this, slow down your heating process or heat your food and hot pack it into jars.

Too Rapid Cooling Phase

Ever opened your pressure canner and pulled jars out and they started sputtering and spitting, especially things like chicken stock? That’s siphoning and it’s caused by changing the outside temperature way too fast with your jars. Or have you ever pulled jars out of the boiling water bath and they spit and leaked and lava-ed food everywhere? That’s also siphoning and it’s because the jars went from a high temperature to a lower temperature much too quickly. To help with this, try to do the cooling phase is stages so there is less sudden changes in temperature. I’ll give examples of how I do it below.

Pressure canning:

After processing time is complete, allow pressure canner to completely depressurize.
Once depressurized, unlock lid and cock it slightly so some steam escapes for 10-15 minutes.
Then, remove lid and allow jars to sit inside the canner with the lid off for another 15 minutes.
Remove jars to a heat proof surface and allow to cool

Water bath canning:

After canning process time is complete, shut off heat and remove lid from canning pot. Allow jars to sit in hot water for 5-10 minutes.
After 10 minutes, remove jars from canner and set aside to cool.

By giving the jars some extra minutes in the canner, you can allow them to adjust a little bit gentler to the temperature changes.

Tightly Overpacked Jars

Yes, you can over pack your jars. If the contents are packed too tightly in there, once they’re heated and expanding in the jar, they’ll push on the lid and push the extra liquid out. You want to make sure you’re only packing jars medium aggressively and not MMA punching the food into them. Calllllm. Caaaaaalllllmmmmmmmm. This is especially important when pressure canning low acid foods, like meats and beans and such, because these swell and grow under the pressure built within the canner and if you’ve overpacked them, you may have more than just siphoning. You may have lids blowing off and that is just and unbelievable mess to clean up when it’s all said and done. Don’t do this.

Not Enough Headspace

I know lots get caught up on correct headspace, and I explain that here. Headspace is really necessary just to leave enough room in the jar between the food and the lid for expansion. If you are filling every jar to the tippy top and then pressure canning them from 90 minutes… you in trouble. That’s why the headspace rules exist. As long as you leave enough, you’ll be fine. Headspace is definitely more important with pressure canning, too, because of that pressure the food goes under and being at a much higher temperature surpassing boiling.

Generally, for pressure canning ANYTHING, usually low-acid foods, you should be leaving 1 inch headspace. I know there’s guidelines to be able to pressure can high acid foods like applesauce and tomato juice and tomato sauce, and I’m telling you, leave that extra headspace and don’t use the 1/2 inch guideline. The lids will blow off or they’ll siphon and it’s a MESS. So just stick to 1 inch headspace if you’re pressure canning and you’ll be fine!

Other less common but possible causes of loss of liquid from your canning jars are over processing and too high of pressure or inconsistent pressure in your pressure canner. These two issues are the easiest to prevent and correct if your jars siphon.

The biggest issue with siphoning with home canning is when you’re canning meat or something with meat in it. Meat has fat in it and fat is greasy and if that gets between the jar rim and the lid, and can cause the lid seal to fail. That’s a huge bummer. But it is also very preventable by using the practices above. If you are raw packing meat, heat it slowly and cool it gently. Don’t be in such a huge rush to yank your jars out of the canner. I know it’s hard, and I’m just as guilty, especially when you’re trying to pack 2-3 or more canner loads into one day. Rushing is what gets me every time and I normally pay for it dearly with failed seals, false seal, and siphoning. Siphoning seems to be the biggest cause of lid seal failure, not the lid manufacturer itself.

Here’s a simple guideline of my workflow for canning hot pack food and also raw pack (cold pack) food into clean jars.

Hot Pack

Hot jars > hot food > hot liquid
Hot water in the pressure canner or the water bath canner
Heat on medium high and can as normal

Cold Pack

Room temperature jars > room temperature food > warm liquid (I would never fill jars with cold or frozen food for canning. That’s just asking for jars to break.)
Warm water in the pressure canner or the water bath canner
Heat on medium low and can as normal (this takes a bit longer to heat up since you need to allow the contents of the jar to heat up with the canner)

I once was canning zuppa toscana and has a big hunk of kale siphon out and get stuck half out of the lid and half in the jar and the lid still sealed!! Food particles between the lid normally affect the seal but that one didn’t. I still didn’t put that on the shelf because I didn’t trust, but I cackled a little. Totally went against everything I preach about siphoning and canning LOL.

Simply try to heat your canner a little more gently if you aren’t hot packing everything and cool everything down a little more slow. We need to practice patience and slow living. Ok?! I’m talking to myself here more than anyone else.