If you are new to canning, you might already know that it isn’t always a straightforward process. Canning requires exactness in measurements, particularly in leaving proper headspace. Understanding each part of the process will ensure that you correctly preserve your food items.
Headspace in canning is the amount of empty space left between the food in the jar and the bottom of the lid, allowing for proper sealing and preservation. When the jar is heated up during processing, the food will expand, creating a vacuum seal. Foods require different amounts of headspace.
There are different methods on how to measure headspace and how much headspace should be left in a jar, but here you will find a comprehensive guide for all of your headspace concerns.
Purpose of Headspace in Canning
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The main purpose of headspace is so that the jars seal properly during processing. If the jars do not seal properly, the food will not be preserved and will spoil.
Processing is the most important part of canning, and if proper headspace is not used, the process will not work. After jars are filled and topped with a metal lid and the outer band, jars are either boiled, steamed, or placed in a pressure canner. During processing, the food is heated up to destroy microorganisms that would cause the food to spoil. As heat is applied, the food expands, and internal pressure within the jar changes. Extra air in the jar escapes through the lid. Because the atmosphere outside the jar is higher pressure than inside the jar, this pulls down the lid onto the jar, forming a vacuum seal.
If there is not enough headspace left in a jar, the food will not have room to expand and could bubble up around the seal of the lid. This excess food around the seal will prevent it from closing completely. Too much headspace in a jar could also result in a false seal because there will not be enough time processing to get all of the air out of the jar, or the air in the jar could cause food discoloration.
How to Check for Headspace in Canning
Headspace is measured in height by inches or centimeters, so a ruler can work to measure headspace, but it can be tricky to be exact.
One canning headspace measuring tool is a plastic stick that often comes with most canning kits, like the Ball Bubble Remover & Head Space Tool on Amazon. This tool has several ridges that look like steps. Each ridge or “step” represents 1/4 inch increments all the way from 1/4 inch to 1 inch. To use the tool, you place the correct ridge on the lip of the jar. The bottom of the tool should just meet the top of the food contents.
Another headspace measure tool is a plastic canning funnel that latches on the mouth of the jar, like this Prepworks by Progressive Canning Funnel for Regular and Wide Mouth Jars that costs about $9 on Amazon. The edge of the funnel indicates the different measurements. Simply place the funnel inside the jar, then fill it with food until it reaches the appropriate mark.
If you don’t have a headspace measuring tool, you can use the threads or the lines that run along the top part (called the finish) of the jar. It is important to note that this method isn’t the most accurate and is the equivalent of “eyeballing” it. The first thread that is closest to the mouth of the jar is the 1/4 inch mark. The middle thread represents the 1/2 inch mark. Just below the last thread is the 1-inch mark.
How Full Should Canning Jars Be?
For any type of food that is canned, some amount of headspace is necessary. When canning, you will never fill the jars so full that the food is touching the lid.
While it is generally acceptable to follow the headspace listed on a recipe, if the measurement goes against the information on the table shown below, it might be worth adjusting.
|Jar Contents||Headspace Required|
|Low acid foods, vegetables, meats, and mixtures of low and high acid foods||1 to 1.25 inches|
|High-acid foods (pickles, relishes, condiments), fruits, and tomatoes||1/2 inch|
|Juice, jams, jellies, and soft spreads||1/4 inch|
Freezing is another canning option for no-cook items that can keep without being heated and vacuum sealed. You will also need to leave headspace in jars when freezing so that the food doesn’t expand and crack the jar. This table shows headspace recommendations for frozen goods.
|Type of Pack||Wide-mouth jar||Regular-mouth jar|
|Liquid Pack*||1/2 inch (pint), 1 inch (quart)||3/4 inch (pint), 1.5 inches (quart)|
|Dry pack**||1/2 inch (pint and quart)||1/2 inch (pint and quart)|
|Juices||1/2 inch (pint), 1 inch (quart)||1.5 inches (pint and quart)|
**Fruit or vegetable packed without added sugar or liquid.
If you still aren’t sure exactly how much headspace would be required for the type of food you are canning, then you can increase the headspace a little more. When in doubt, round up rather than down.
Altitude Adjustments in Canning
Canning instructions are based on sea-level altitudes, but if you live in a high-altitude location, you will need to make adjustments to your headspace and processing times.
Pro Tip: For more information on altitude adjustments in canning, check out my article, How Altitude Impacts Canning | How to Adapt Canning Recipes Based on Your Altitude
For every 2000 feet above sea level, the pressure in the canner must be increased by one pound of pressure. Additional time would not be needed in a pressure canner if the pressure amount is adjusted. For every 1000 feet above sea level, you will need to increase the headroom by 1/8 inch, but not to exceed 1.75 inches for quarts, 1 inch for pints, and 3/4 inches for 1/2 pints. (Source)
Canning can be tricky, but the results are so worth it! There is nothing like having summer peaches in the dead of winter or delicious homemade salsa for taco night. It is a great way to reduce waste, and it is a great feeling to be able to make and process your own food.
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Here are some of my favorite canning tools
Thank you for reading this article. I hope you found it helpful as you strive to stock your pantry with delicious home-canned food! Here are some tools that I use as a canner that I’m hoping you’ll also find helpful. These are affiliate links, so if you do decide to use any of them, I’ll earn a commission. Please know that these are the tools that I actually use and recommend and believe in 100%!
Nesco Smart Canner: You can see that many of the posts on my site show me using the Nesco canner. This is by far my favorite canner to use, and because of that, it’s the one that I recommend. Note that the Nesco and Carey Smart Canners are the exact same thing. So, if you go to Amazon and see that Nesco canners are out of stock, but the Carey is available (or cheaper!), then by all means buy a Carey. As long as you have either a Nesco or Carey, you can follow along with what I demonstrate on this blog.
Tattler Reusable Lids: I use both Tattler and Harvest Guard reusable canning lids. They are both American made, made by the same family. I prefer to buy my Tattler lids from Lehman’s, since they are a small, family-owned company. You can get Tattler lids from Lehman’s here, but if you prefer to buy from Amazon, you can get them here.
Metal Canning Lids: I have always been a fan of Ball canning lids. However, due to cheap knock offs on Amazon that claim to be Ball lids, I no longer purchase them from Amazon. You can get them from Lehman’s here. Another solid brand that Lehman’s sells is Superb. They are thicker and seem to have better quality gaskets. Here are the regular mouth lids and here are the wide mouth lids.
Norpo Canning Tools Boxed Set: I love this set of canning tools because it truly includes all the basics that you need, whether you’re water bath or pressure canning. Occasionally I’ve lost one of the items in the set and to replace it, had to buy it separately. It’s definitely more cost effective to buy the entire set.
The Ball Complete Book of Home Preserving: This is the first canning book that I purchased, and it’s still the one that I refer to most often. Especially when you’re first learning to can, it’s important to use trusted recipes and instructions that you know are safe. This book provides some great canning recipes to get you started, and also gives a lot of great “how to” canning information. When in doubt, look it up in the Ball Complete Book of Home Preserving!