You Asked It!

Tag: Food Preservation

Preserving Unripe Tomatoes

tomatoesAs fall approaches, those end of season unripe tomatoes are still usable. Be sure to pick them before a frost or freeze if canning them.

Unripe, or green, tomatoes can be preserved just like ripe tomatoes. So when canning them they still require acidification. Here are some ideas to can green tomatoes.

Don’t want to can them, or it is after a frost or freeze? Then freeze them for later use.



Fall Canning Tips

At this writing, the calendar still says summer, but there is a fall feel. Gardens may still be producing, so here are some end-of-season tips for food preservation.

Done canning? Store your equipment with care for next season.


Pressure Canning Done Right

During this pandemic, more gardens were planted and now they are producing some great crops! So when those tomatoes all ripen at the same time, what can you do? Preserve them!

Pressure canning is used to preserve vegetables and meat, including many tomato products. Vegetables and meat are low acid foods and require pressure canning to destroy C. botulinum, the pathogen that causes botulism.

It is critical to follow the directions in using pressure canners. Always read the instruction manual for your canner. Do a practice run with water in the canner to learn how to use it and how it works with your stove. Check your stove manufacturer to be sure canning is recommended. Some glass top stoves are not suitable for canners as they can crack under the weight of a heavy canner.

Learn more about safe pressure canning in the How-to Guide to Pressure Canning. It is also available in Spanish.

Take Time to Vent!

When using a pressure canner, it is very important to vent the air out of the canner before pressurizing. Air trapped in a pressure canner lowers the temperature obtained for a given pressure (for example, 10 or 15 pounds pressure) and results in underprocessing. To be safe, USDA recommends that ALL pressure canners must be vented 10 minutes before they are pressurized.

To vent a canner, leave the vent pipe (steam vent) uncovered (or manually open the petcock on some older models) after you fill the canner and lock the canner lid in place. Heat the canner on high until the water boils and generates steam that can be seen escaping through the open vent pipe or petcock. When a visible funnel-shape of steam is continuously escaping the canner, set a timer for 10 minutes. After 10 minutes of continuous steam, you can close the petcock or place the counterweight or weighted gauge over the vent pipe to begin pressurizing the canner.


The Importance of Headspace in Canning

Leaving the specified amount of headspace in a jar is important to assure a vacuum seal. If too little headspace is allowed, the food may expand and bubble out when air is forced out from under the lid during processing. The bubbling food may leave a deposit on the rim of the jar or the seal of the lid and prevent the jar from sealing properly. If too much headspace is allowed, the food at the top is likely to discolor. Also, the jar may not seal properly because there will not be enough processing time to drive all the air out of the jar.

The amount of headspace depends on how much the food moves or swells inside the jar during the canning process. In the case of spaghetti sauce, there is a lot of food material and more viscosity or thickness compared to a tomato juice. So the food pulp/pieces are going to shift or swell more than a juice, therefore they need more room. Also, how the heat moves through the jar, by convection or conduction, can influence the amount of headspace needed.

Reliable recipes will specify the amount of headspace needed for that product. In general, jams and jellies are 1/4 inch; pickles, fruits, some tomato products are 1/2 inch; and plain vegetables and meats are at least one inch.


Canning Tomatoes and Added Acid

In short, it is not a suggestion, but a requirement to add acid to home canned tomatoes. This is for water bath AND pressure canned tomatoes. Why you ask?

Tomatoes that are acidified for canning are done so to prevent botulism poisoning and other bacterial concerns by a combination of acid and heat. The prevention control in vegetables, meat and other naturally low-acid foods is by heat alone.

Tomatoes can have a natural pH above 4.6 (at least up to 4.8).  But rather than develop a pressure-only process as if they were all low-acid, since they are so close to 4.6, USDA decided instead to recommend adding a small amount of acid so they can be treated as a food with a pH less than 4.6 for home canning.  Therefore, they are suitable for boiling water canning when the acid is added.  (The commercial industry often also adds citric acid to tomatoes to be able to give them a less severe heat treatment than would be needed for botulism and other bacterial controls.)

Sources: and


The Search for Canning Supplies

Gardens popped up in a lot of new locations this year since everyone had more time at home and many garden supply stores sold out of plants and seeds. Now that gardens are producing, food preservation supplies are disappearing off store shelves.

Canning lids are few and far between. But remember, do not reuse canning lids! Do not use old, dented, or deformed lids, or lids with gaps or other defects in the sealing gasket. When jars are processed, the lid gasket softens and flows slightly to cover the jar-sealing surface, yet allows air to escape from the jar. The gasket then forms an airtight seal as the jar cools. Gaskets in unused lids work well for at least 5 years from date of manufacture. The gasket compound in older unused lids may fail to seal on jars.


Canning Tomatoes: Don’t Forget the Acid!

Tomatoes may have that tasty zing that makes them tart and tasty. But in reality, they are not as acidic as they seem, especially when canning tomatoes.

Tomatoes have a pH value around 4.6 which makes them unsafe to can by themselves, with many varieties above 4.6. All tomatoes must be acidified with either citric acid, bottled lemon juice, or vinegar with 5% acidity in both water bath and pressure canning processing.

Without this added acid, tomatoes will likely ferment and spoil. Learn more in Preserve it Fresh, Preserve it Safe: Tomatoes.


Why Do Home Canned Foods Lose Liquid?

The headspace for most tomato products should be 1/2 inch.

As with any problems when cooking, there are many reasons to answer a question.  For pressure canning, here are some reasons for the question above:

  • Improper headspace to allow for food expansion.
  • Pressure canner was not exhausted for 10 minutes before pressurizing.
  • Pressure too high.
  • Unsteady heat source caused pressure fluctuation.
  • Removing pressure regulator before pressure dropped completely.
  • Rapid temperature changes or drafts blowing on the canner.
  • Lids not applied correctly.
  • Raw pack was used instead of hot pack.
  • Did not leave canner closed for 10 minutes after pressure dropped completely.

Source: and


Are White-Fleshed Peaches Safe to Can?

There is evidence that some varieties of white-flesh peaches are higher in pH (i.e., lower in acid) than traditional yellow varieties. The natural pH of some white peaches can exceed 4.6, making them a low-acid food for canning purposes. At this time there is no low-acid pressure process available for white-flesh peaches nor a researched acidification procedure for safe boiling water canning.

Freezing is the recommended method of preserving white-flesh peaches.

For instructions on freezing peaches, see Preserving Peaches at

Source: Dr. Elizabeth Andress, University of Georgia Extension