Here's what you need to know about canning tomatoes this season

Here are some common conditions that can occur when canning tomatoes and ways to prevent from Iowa State University Extension and Outreach.

Floating tomatoes (tomatoes or tomato pieces at the top of the jar, liquid at the bottom) may be a visual disappointment but does not affect the safety of the product. Floating is more likely with whole or quartered tomatoes and with a raw pack.

Float can be minimized by choosing fresh, firm tomatoes, reducing the amount of liquid in the jar (replacing with product), packing the jar as firmly as possible without crushing the tomatoes, and removing air bubbles. Canning crushed tomatoes and/or using a hot pack often eliminates the problem.

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Separation: Sometimes crushed or puréed (juice) tomatoes will separate in the jar into tomato solids and liquid. Separation is another visually disappointing issue that does not affect safety. When tomatoes are cut or crushed before heating, exposure to the air activates a natural enzyme that breaks down pectin, which causes the liquids and solids to separate.  Heating tomatoes immediately after they are cut or crushed to 180 F inactivates this enzyme.

Loss of liquid does not cause food to spoil, though the food above the liquid may darken. If at least half of the liquid is lost, refrigerate the jar(s) and use within 2 to 3 days. Jars with milder liquid loss should be used first.  Penn State Extension advises that the causes of liquid loss during processing of tomatoes or other fruits and vegetables is raw pack, rapid fluctuation of temperature in the canner, and removing the jars too quickly after processing. Improper headspace and loose bands are other sources of liquid loss.  Food expands during processing and if a jar is overfilled there is insufficient room for the expansion.  When this happens, water will push out to make room for expansion. If canning ring bands are too loose, liquid will escape and may also cause seal failure. Removing air bubbles from the jar prior to lidding helps to lessen liquid loss.

Air Bubbles:  Removing air prior to processing is an important step in canning. Air trapped in jars can interfere with the jar’s ability to drive out the extra air in the top causing too much headspace, floating, loss of liquid, and a poor or no seal. Additionally, too much air space results in canned product above the canning liquid which can lead to discoloration and the development of off-flavors. A heat resistant plastic or silicone knife or spatula handle works well.  Do not use anything metal to remove air as this may cause hairline cracks in the jar.  Simply run the tool around the edges of the jar, gently shifting the food, so that trapped air is released. More liquid may need to be added to ensure proper head space.

After processing, tiny air bubbles may be noticed.  If these bubbles are inactive, they are harmless. But if the bubbles are actively fizzing up to the top of the jar when opened, the product may be fermenting or contaminated and should not be used and properly discarded.

For more information on home canning, go to the Cornell Cooperative Extension of Herkimer County website at https://bit.ly/CCEHerkFoodPreservation.

Linda Robbins, CDN, is assistant director and nutrition educator for Cornell Cooperative Extension of Herkimer County. 

This article originally appeared on Times Telegram: Tips for canning homegrown tomatoes