Pressure Canning Problems: Siphoning (Missing Liquid)

When it comes to pressure canning people often share two related problems:

  1. Jars enter the canner full of liquid and when processing finishes you are surprised to see how much liquid is missing.  The outside of the jars are a little dirty and it appears that liquid has siphoned from inside, out.
  2. Related to question 1; is it ok to still eat preserved (and pressure canned) food that is missing a lot of liquid?

People often ask question 2 without resolving question 1 first.  I say this because I was one of them – I was so focused on what to do with the ‘problem jars’ after processing that I missed getting to the root of the problem and preventing them all together.

And, while I have the occasional jar that siphons, it’s an extreme rarity.  So, let’s start there..

How to Reduce/ Virtually Eliminate Siphoning While Canning (and Pressure Canning)

I used to suffer from siphoning on a routine basis.  It happened almost every time I pressure canned and quite often when I made pickles and other water bath preserves. I was getting frustrated with my results when this happened:

  • The timer went off in my kitchen and I turned the heat off.
  • I carefully moved the canner from the electric element (where it sat) and moved it to a cool element to cool it faster.
  • I wasted a few minutes and, being impatient, I put a steam-resistant oven mitt on and, against all warnings (do not do this), I removed the weight on the top of the canner.  This let the pressure out quicker so I could open it sooner.
  • I waited a while until I could open the canner.  I tried a few times to open it so I wouldn’t lose any time (I have no idea why I was in such a rush).
  • I grabbed my tongs, pulled the jars out and sat them on a rack.  I watched the jars closely and was amused to see the liquid still boiling inside.
  • I walked away.  Everything seemed fine.
  • I checked my jars a few hours later.  The counter was wet and the jars had siphoned.

Let’s be clear: don’t do the above.  I messed up for your benefit!

I wasn’t certain but I had my first theory: rapidly cooling the jars forces air lout of the jars at a faster rate than naturally cooling and this increased pressure pulls the liquid out.  I don’t know if my theory is scientifically correct – but letting the jars cool naturally has all but solved my siphoning problems!

When waterbath canning I simply turn the heat off and let the jars remain in the waterbath for a few minutes to slightly lower the temperature.  5 or 10 minutes is generally enough.  Then proceed as you normally would.

When pressure canning, I turn the element off and walk away.  I don’t open the canner until it easily opens on it’s own.

Is it safe to eat Preserved food that’s siphoned (missing liquid)?

I often worry when answering questions on safety here; and I tend to avoid them like the plague.  I’ve also written on why you probably shouldn’t blindly trust me or other food bloggers without assessing the risk for yourself.

And, the good news here, is that you don’t have to trust me!  Check out these guidelines from the University of Minnesota Extension Office:

Loss of liquid does not mean that the food is unsafe to eat. However, food above the liquid may discolor during storage.  Use those jars first. If the loss of liquid is excessive (i.e. at least half of the liquid is lost), refrigerate the jar(s) and use within 2-3 days.
The extension office publishes a wonderful newsletter (linked above) – it has some amazing information on pressure canning and more information on troubleshooting siphoning!

Closing

What questions do you have about pressure canning?  We’ll be sharing more about it this week as well as featuring a big round-up on pressure canning in the weekly newsletter this weekend (you can sign up here).  Thank you to Casey for inspiring this article on our Facebook page!

 

Comments

  1. Rodney R says:

    The physics behind what is happening can, most probably, be explained as follows: The boiling point of water is determined by the pressure it is subjected to. At sea level (14.7 psia) water boils at 212 F (100 C). When the water is placed into the pressure canner and turned on with a plan to maintain a pressure of 10 psig (24.7 psia), the water begins to boil at 212. After the water begins to boil, steam venting and the weight is set or petcock closed the pressure from water expanding and turning to steam causes the pressure to increase. If the pressure is maintained at 10 psig the temperature will be 240 F (per Keenan and Keyes, Thermodynamic Properties of Steam). At the end of the processing time the temperature of the liquid in the jars will also be 240 F. Because the pressure in the canner is at 10 psig the entire system is balanced so the pressure inside and outside the jars is the same. Removing the heat will cause the pressure to slowly drop both outside and inside the jars provided the weight is not removed or Petcock opened. If the jars are taken out of the pressurized environment by opening the petcock, removing the weight or just opening the whole thing up prior to reaching 212 F they will begin an active rolling boil and the pressure in the jars will be higher than the pressure outside the jars. It is basically boiling over and some liquid will come out. Once the temperature of the jars falls below 212 F the lids should reseat themselves as they would in water bath canning. Just like water bath canning lids that don’t get sucked down are not to be trusted.

    • Rodney,

      This may be my all-time favorite comment ever. THANK YOU!

      I recently reada quite from someone (I think they claimed it was Einstein) that essentially said, “If you can’t explain something simply then you don’t understand it.”

      Your explanation totally makes sense and was easy to follow, despite my lack of understanding of Physics. Fantastic – thank you! :)

  2. Rodney R says:

    You Welcome and THANK YOU for all of your work on WellPreserved. It has taught us a lot. Looking forward to reading many more posts.

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