Hubbard Squash

It has been a good number of years since the last Hubbard squash harvest because we just never planted anymore. But we also had a good number of canned squash still in our pantry. The last time I canned it, I made it into a cooked puree and canned it in a pressure canner at high pressure for a long length of time. Since that time though, the USDA has since withdrawn their guidelines for canning pureed squash due to inconsistencies in preservation. I can attest, we saw some of those inconsistencies. Some jars looked nice and had plenty of moisture but others over time looked dry and eventually discolored on the top. We ate the nice looking stuff and all that was left was the dry, discolored looking squash which we tossed into the compost bin. 

Per new recommendations, I decided to try again but this time cubing the squash up raw and hot packing it into the jars. I cut up the squash above and it made 12 pints of cubed squash. Per recommendation, I canned it at 15 pounds for 55 minutes for pints and ended up with mixed results. Below are the good results. The squash cubes look beautiful sitting in plenty of liquid. But half of the jars ended up losing about half or more of their liquid. After searching, it is called siphoning in the canning world and happens. There are a number of causes for it. One cause is that I didn't follow the headspace criteria to the letter. It called for 1 inch of head space and I was probably pushing a half inch in some of the jars. Another is that I should hot bath my empty jars before filling. I usually do especially in water bath canning, but since this was going to be under pressure for a lengthy amount of time, I thought it unnecessary for killing bacteria. It turns out that is true but it is necessary to help reduce the amount of siphoning that happens. Another thing I learned is that I am supposed to let the canner pressure dissipate naturally and then after removing the lid, leave the jars in the water for another 10 minutes before removing. I was in a hurry to meet a timeline and so I aided removing the pressure by holding up the release valve and then removing the jars immediately.

So, I have a number of things to try differently to try and reduce the siphoning from happening because a 50% loss is quite discouraging. From what I have read, the siphoned pints are still good to eat but like my previous canned puree jars, will slowly dry out and discolor on top so are best eaten sooner rather than later. Pumpkin pies are in my future I guess. All this also probably explains what happened to those canned purees that I did eight years ago. They probably siphoned but because it was a puree, I just didn't notice until they started discoloring. 

What I still don't understand is why I haven't seen this on anything else? Either is is something specific to squash or most likely, it is just a function of time and pressure since I don't can anything else at such a pressure or length of time. I'm still learning after all these years.

Post Addendum: The next day after heating up the jars in hot water, I opened up the six pints and topped them off with more boiling water being careful not to exceed the headspace allowance. I put new lids on them and recanned them the full 55 minutes and then let the pressure gradually dissipate on its own. When I finally removed the lid, one jar spit up about a half tsp of water and then stopped. All still had full amounts of water to cover the squash and sealed. A few days later I did another batch using a fresh squash and also did not have any issues with siphoning. So I think head space is definitely something I need to be more aware of and also to not get in a hurry in getting the jars out of the canner.