Canning 101: Tomato Float, Sauce Separation and Loss of Liquid

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Tomato canning season is here and so I’ve been getting a lot of questions from people who are canning their own tomatoes for the first time. They worry because their tomatoes are floating, their crushed tomatoes have separated or their jars have lost significant liquid in the canning process and now they’re not sure if their tomatoes are safe. Let’s take these three topics one by one and put your hearts at ease, shall we?

Tomato Float
Take a look at the jars on the left in the picture above. Those are the whole, peeled tomatoes that I canned last year. As you can see, the tomatoes are floating over a good inch of liquid and tomato sediment at the bottom of the jar. This one is absolutely no big deal.

Even the most seasoned canner is going to have some canned whole tomatoes that float. This is because there are air pockets inside those tomatoes and when you pack something with some internal trapped air in a liquid, it will float.

You can try to avoid float by using regular mouth jars (the shoulders of the jar help keep the fruit in place) and packing the jar as firmly as possible (without totally crushing the tomatoes). But really and truly, it’s no big deal.

Tomato Separation
Often, I will hear from people who are concerned because their crushed tomatoes have separated into a layer of liquid topped by a layer of solids. What happened here is that you heated your tomatoes for more than five minutes, let them cool and then heated them up again.

By doing this, you’ve broken down the pectin inside the tomatoes. In this situation, the pectin was there holding the structure of the cells together and once it goes, there’s nothing to maintain the integrity of the tomato flesh together and so pulp separates from the water.

I never worry about this one either. Just give the jar a good shake before using.

Liquid Loss
Back to the picture up at the top. Take a look at the quart jars on the right. You might notice that several of those jars lost a TON of liquid. I canned that particular batch in my pressure canner and during the cooling process, they siphoned like mad (that’s the official canning term for when liquid escapes).

Siphoning can be prevented by better bubbling of jars and a slower cooling process. However, even when you’re careful, it still happens sometimes. However, as long as your seals are good, jars with even significant liquid loss are still safe to eat.

You may experience some reduction of quality over time and when it happens to lighter colored foods (like peaches), the product that’s not submerged will begin to discolor. Put those jars at the front of the queue of jars to use and don’t worry about it.

Air Bubbles
Sometimes, you’ll preserve tomatoes and once the jars are sealed, you’ll notice that there are a few air pockets or bubbles in the finished product. As long as the lids remain sealed and those bubbles aren’t actively moving around on their own, the jars are fine. Once a jar is sealed, air pockets are only a problem if they seem to bubbling independently of you moving or tapping the jars, as that can be a sign of fermentation. Otherwise, all is well.

What other tomato questions do you guys have? Let’s hear it!

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272 Responses to Canning 101: Tomato Float, Sauce Separation and Loss of Liquid

  1. 151
    Heather H says:

    I have some canned tomatoes I’d like to use (canned this summer, but not by me). They didn’t appear to have bubbles when I picked them up, but once I sat them on the counter, I saw bubbles around the top of the liquid. I will be using the sauce in a meal that my one year old son will be eating, so I’m nervous as to whether the canned tomatoes are safe to use. Thanks in advance!

    • 151.1
      Marisa says:

      Surface bubbles aren’t an issue. It’s only trouble if the jars have been sitting still and untouched for some time and there are bubbles that are still moving.

      • Stacy says:

        I canned raw tomatoes according to the Ball canning recipe. When quartering the tomatoes I scooped out a lot of the clear gel with seeds. I packed the jars full and removed air bubbles. I pressure canned them to be safe. When they were done and I removed them from the canner (most seemed to have ‘popped or sealed already in the canner) and they were cooling on the counter, the jars were full, tomatoes on top and liquid on bottom. Pretty quickly, I noticed air bubble rising to the top of the jar. About 2 hours later, I noticed the liquid on the bottom, solid tomatoes in the middle and about an 1-2 inches of air on top. No more air bubbles are rising. Are they safe? How will I know if they are not? Thank you.

        • Marisa says:

          They are totally safe. You’ll know that they’re not safe if the seals break or if the jars have been sitting along for a while and there are actively moving bubbles rising towards the top.


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