Why Do Tomato Seeds Turn Black When Canned?

Canning tomatoes is a long process, so it can be frustrating to see the seeds have turned black when you open the jar. However, that doesn’t always mean that you need to throw out the food since black seeds aren’t always a sign it’s spoiled.

Tomato seeds turn black when canned because they react with minerals in the water used to can them. Iron, in particular, can cause discoloration in tomato seeds. As long as you sealed the jar correctly, the tomatoes shouldn’t have gone bad. You’ll need to check for signs of spoilage in the food.

In this article, I covered everything about why your tomato seeds might turn black during canning. Black tomato seeds usually aren’t a sign that your food went bad, but it’s always good to check before you eat them. Here’s what you need to know.

Common Reasons Tomato Seeds Turn Black After Canning

There are a few reasons tomato seeds turn black after you can them. Although, it’s worth mentioning that you probably don’t have to worry if you notice this happening. There are two leading causes why the seeds turn black, and neither means the food went bad or is dangerous to eat.

Below, I’ll break down the common causes of black seeds in canned tomatoes.

The Tomatoes Were Overripe

First, it’s not uncommon for tomatoes to naturally have one or two black seeds. You may not have seen them while canning and just noticed them now. If this is the case, you don’t need to worry. All it means is the tomatoes you used were overripe.

Overripe tomatoes make dark seeds, which means they’re ready to germinate. The seeds turn dark and start to sprout in the tomato. It’s a natural process in many fruits; eating the seeds won’t hurt you. Since you cooked the tomato before canning it, then gave it an air-tight seal, there shouldn’t be any bacteria growing on the seeds.

If you’re growing your own tomatoes, it’s possible you accidentally let them overripen. Overripe tomatoes are safe to eat unless they feel mushy or smell bad, so you should still be able to eat them without issues.

Overripe tomatoes usually only have a few dark seeds. So not all of the ones you canned will be black, even if you put many tomatoes in a single container. If most of the seeds are black, then it’s probably from a different cause.

The Seeds Reacted to Minerals in Your Water

It’s also possible that the tomato seeds reacted to the minerals in your water. When canning food, you need to wash the produce first. However, depending on where you get your water, there may be minerals in it. 

These minerals can interact with the seeds and cause them to turn black if the water remains in the can for a long time. Iron is the mineral most likely to discolor the seeds, so if you have hard water at home, this is most likely the cause.

The iron in the water shouldn’t hurt you, so the tomatoes should still be safe to eat. If this happens, then more of the seeds will be black.

Are Tomatoes With Black Seeds Safe To Eat?

Tomatoes with black seeds are safe to eat. You’ll want to check the canned tomatoes carefully. If only the seeds are black, it’s OK to eat. However, you don’t want to eat canned tomatoes where the fruit is black, which indicates spoilage.

So, black tomato seeds are safe to eat most of the time. Usually, they turn black when exposed to minerals, or the tomatoes were overripe when you canned them. These causes aren’t harmful to us.

Although, the seeds can also turn black if mold grows on them or bacteria attack the surrounding fruit, which would be harmful to you to eat.

Because of this, you’ll want to make sure that you can recognize rotten tomatoes. While canning your food can make it last much longer, it will go bad if you don’t seal the container properly. In those cases, there will be other signs that the tomatoes aren’t safe to eat, such as a foul smell.

It is dangerous to eat spoiled food, so you should throw out any canned tomatoes you’re unsure of.

Signs Your Homemade Canned Tomatoes Are Spoiled

If you notice spoilage in your homemade canned tomatoes, you’ll want to throw them away. 

Here’s what you should look for:

  • The tomatoes’ flesh is discolored, not just the seeds. 
  • The jar smells strange when you open it.
  • You can’t remember when you canned the tomatoes.
  • The lid is bulging or leaking.
  • The container is cracked.
  • The tomatoes look cloudy.
  • There are signs of mold on the tomatoes.

According to the CDC, botulism from canned food is a severe illness. If you’re unsure of your canned tomatoes, throwing them away is always better than risking your health. Never taste the tomatoes first to tell if they went bad— even a small amount of contaminated food is hazardous.

How Long Do Canned Tomatoes Stay Good?

According to the USDA, canned tomatoes can stay suitable for up to 18 months if you can them carefully. They’re a high-acid food, so they don’t last quite as long as other foods with less acid.

Overall, you need to record the dates you canned your food on the containers or somewhere you won’t forget to check. If more than 18 months have passed since you canned the tomatoes, and you’re questioning if they’re still safe to eat, throw them out.

How To Prevent Canned Tomato Seeds From Turning Black

Black seeds in your canned tomatoes usually aren’t a problem. However, you can still prevent the seeds from changing.

You’ll need first to ensure you don’t use overripe tomatoes. It’s easy to identify overripe tomatoes since they start to wrinkle and feel a bit soft. Perfectly ripe tomatoes are firm, have a strong earthy smell, and are a pleasant red color— not orange or green. They shouldn’t have black seeds at this stage.

Then, you’ll want to use a source of water that doesn’t contain minerals, such as distilled water, during the canning process. Many people enjoy cooking and canning their food using distilled water. Since there are no minerals in this type of water, it can also make the food taste better.

In short, you can prevent the tomato seeds from turning black by addressing the two main problems that cause discoloration. Of course, the best way to avoid this would be to remove the seeds entirely before you can the tomatoes.

(PAA) Do You Take the Seeds Out of Tomatoes When Canning?

You can take the seeds out of tomatoes when canning them. Many people do this because they don’t like the texture of the seeds in their food. For example, you probably wouldn’t want seeds in your homemade tomato sauce. It’s easier to remove the seeds before canning, too.

First, you need to remove the tomato skins to reduce the likelihood that bacteria will get into the canned food.

Follow these steps to peel the tomato and get the seeds out:

  1. Fill a large container with cold ice water.
  2. Boil a pot of water on your stove.
  3. While waiting for the pot of water to boil, cut the top of the tomatoes into a cross shape.
  4. Gently set the tomatoes in the boiling water for about 30 seconds using a ladle or other tool. Remove them when you see the skin peeling around the cut you made.
  5. Move the tomatoes to the ice water and let them sit until they cool about two or three minutes.
  6. Drain the cold water and dry off the tomatoes with a paper towel.
  7. Peel the skins and cut the tomatoes into sections.
  8. Remove the center of the tomatoes with your hands or scoop them out with a spoon.

If you’ve had issues with your canned tomato seeds turning black in the past, you can always remove them next time. Most people remove the seeds because they don’t like the texture they add to recipes, but you don’t always need to.

Overall, it’s up to you if you want to deal with removing the seeds from your tomatoes. However, you must always peel the skins off to sanitize your canned food.

What Color Should Tomato Seeds Be Before Canning?

Typically, most tomato seeds are a light yellow color. They can also be yellow-green or slightly darker and don’t turn black until the tomato becomes overripe. Even then, only a few of the seeds darken.

The tomatoes you use for canning should have seeds that are light yellow since it means that the tomatoes are healthy and safe to eat.

Final Thoughts

To summarize, there are two main reasons why tomato seeds turn black when canned. The most common reason is that the tomatoes were overripe when you canned them. Secondly, the seeds might’ve reacted to minerals in your home’s water, causing them to darken.

If either of these situations happens, the tomatoes are still safe for you to eat. However, just in case, you’ll want to know more about recognizing spoiled canned tomatoes since the fruit can turn black when they go bad.

Alexander Picot

Alexander Picot is the principal creator of TheGrowingLeaf.com, a website dedicated to gardening tips. Inspired by his mother’s love of gardening, Alex has a passion for taking care of plants and turning backyards into feel-good places and loves to share his experience with the rest of the world.

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