The National Center for Home Food Preservation advises against doubling recipes for home canning for several important reasons:
Jams and Jellies: Doubling recipes can disrupt the balance of ingredients, potentially preventing the batch from setting properly. It also increases the cooking time, which may result in undesirable textures such as rubberiness or even burning of the jam or jelly.
All Recipes: Doubling a recipe can negatively affect the quality of the final product. It may cause uneven cooking before processing and increase food safety risks, as the additional product may sit in jars for extended periods before processing. This can result in a lower initial temperature, potentially leading to underprocessing.
For optimal safety and quality, it is recommended to prepare home-canned goods in individual batches as directed in the recipe.
Newsflash
Celebrate Giving Tuesday with the National Center for Home Food Preservation!
This Giving Tuesday, help the National Center for Home Food Preservation continue its mission to empower individuals and families to safely preserve food at home. Your generous donation will support our efforts in providing reliable, research-based information and resources to ensure safe food preservation practices across the country.
By giving today, you’re supporting:
Educational materials on safe canning, freezing, drying, and fermenting
Ongoing research to enhance food preservation knowledge
Workshops and training programs for Extension agents to provide up-to-date information in their communities.
Join us in making a lasting impact and ensuring that home food preservation continues to be safe and accessible for everyone. Donate today and help us spread the joy of preserving food safely for generations to come.
Newsflash
May canned food be reprocessed if the lid does not seal?
Sometimes a jar in a canner load fails to seal upon cooling. This may happen because of a cracked or nicked jar, or perhaps because food is fouling the jar rim where the lid sits. Due to loss of quality, reprocessing of jars is not recommended.
If you do reprocess, follow these steps for a safe product:
1. Re-process within 24 hours. For a safe final product, you must have followed an up-to-date research-tested recipe on your first attempt, and you must reprocess within 24 hours.
2. Remove the lid and empty the contents of the jar into a large pot and heat to boiling.
3. Fill a clean jar with the heated food, remove air bubbles, and top with a new lid.
4. Reprocess using a tested recipe for a hot-pack product. If there is no tested hot-pack recipe, the product may not be safely reprocessed.
If you did not follow a tested recipe on the first try, all jars, sealed or unsealed, may be unsafe and should be discarded.
To preserve quality of food where jars failed to seal (and discovered within 24 hours of initial canning), refrigerate the jars and consume contents within one week. Unsealed jars may also be frozen for up to one year, be sure to adjust headspace to 1” before freezing.
Safe home canning: the importance of using tested recipes
Whether you are home canning as a hobby, entering your products in local fairs, or preserving food for your family, it is essential to prioritize food safety. Due to safety concerns, the National Center for Home Food Preservation (NCHFP) strongly advises using only tested recipes from reliable sources for all home canning. Sources include the USDA, NCHFP, and other university extension resources. While you may find many canning tips and recipes online, not all of them are safe or accurate—just because it's on the internet doesn't make it true. Using untested or unsafe methods can increase the risk of foodborne illness, particularly botulism, a potentially fatal illness caused by improper canning practices. By following tested recipes, you ensure safe preservation techniques that protect your health and prevent contamination by dangerous microorganisms.
Newsflash
Why Should You Peel Tomatoes Before Canning?
The National Center for Home Food Preservation continues to recommend peeling tomatoes for canning, unless specified otherwise, because most tested recipes were developed with the skins removed, and the processing times are based on peeled tomatoes. Skins may interfere with heat penetration during the canning process, leading to under-processing and potentially unsafe products. Additionally, removing the skins not only enhances safety by reducing the bacterial load but also improves the texture and flavor of the finished product. Tomato skins tend to leave tough, chewy bits and can impart a bitter taste to your canned goods.
Newsflash
Canning on Portable Burners
Can I can on portable gas or electric burners?
If you have a smooth cooktop and the manufacturer says not to can on it, then you might find yourself looking for an alternative. The alternatives for canning (if you have one of these no-canning recommended smooth cooktop ranges) are either to purchase and install a permanent set of electric coil or gas burners as a range top (without an oven) or to purchase a portable electric coil or gas burner.
And that is where important decisions come in to play. An installed range top requires the utilities to support it and can be quite expensive as a second range top. As for portable burners, they are not all alike and not all portable burners are appropriate for canning. First of all, check the burner manufacturer's specifications and directions or contact their customer service department for more specific information about the appropriate use of a particular burner for canning.
We cannot endorse a particular brand, but here are a few basic guidelines for you to keep in mind when selecting a portable burner for canning purposes:
1. The burner must be level, sturdy, and secure. Look for enough height to allow air to flow under the burner, but not such that it will become unsteady with a full, heavy canner resting on it. One we have tested was about 4 inches high off the counter top, on short legs that allowed air circulation underneath but was plenty stable.
2. Look for a burner diameter that is no more than 4 inches smaller than the diameter of your canner. In other words, the canner should not extend more than 2 inches from the burner on any side. This is a common recommendation, but also make sure this is the recommendation for your canner brand.
3. For electric burners, you want the wattage to be about equal to that of a typical household range large burner. We have been successful bringing a boiling water canner to boiling with one that is 1500W/120V, but household range burners are more typically 1750W or higher and this kind of wattage may actually be a better choice if you can find it. We have not yet tried using a pressure canner on a portable electric burner.
4. You want the burner to have housing that will hold up to the high heat under the canner for long heating periods, and not damage counter tops with reflected heat. We contacted a foodservice supply store to help us identify one like this; it cost us about $200. We used it successfully a few times to bring water to a boil, but have not used one repeatedly for canning.
5. At least one pressure canner manufacturer advises not to can on any outdoor heat source. Your pressure canner can be damaged if the gas burner puts out too much heat. Higher BTU burners (over 12,000 BTUs) could also produce so much heat that the recommended come-up time for canning could be altered, potentially producing an unsafe final product.
6. Again, check manufacturer’s directions and/or contact their customer service for more information about appropriate burners. When you are asking manufacturers about canning, specify whether you are asking about pressure canning (much more heat concentration) or boiling water canning. If the manufacturer's directions have been followed, and canning problems occur, then you must take it up with the manufacturer.
February, 2024 National Center for Home Food Preservation
Newsflash
Pre-Sterilizing Jars before Canning
Do I need to pre-sterilize my jars for canning?
New canning jars out of the box are not sterile. Being in a box or covered in plastic wrap is not the same as a sterile environment. In addition to contamination by microorganisms that cannot be seen with our bare eyes, packaged jars may accumulate dust, small bits of debris, and even chips of glass in the case of breakage (which does happen sometimes in all the steps of transport from factory to store to home).
Whether brand new or re-used many times over, you should always clean jars just prior to filling them when canning. Wash jars in a dishwasher or by hand, using detergent and rinsing well. Clean jars should then be kept warm prior to filling. You can leave them in the closed dishwasher after the cycle, or use your canner as it is preheating, or create a separate water bath that will keep the jars both clean and warm.
Washing is also a good time to inspect jars for any cracks or chips, discarding or re-purposing those jars for non-canning uses if any imperfections are found. If you see scales or film from hard water left on your jars, then remove this by soaking jars for several hours in a solution containing 1 cup of vinegar (5% acidity) per gallon of water.
In order to actually sterilize jars, they need to be submerged in (covered by) boiling water for 10 minutes. When the process time for canning a food is 10 minutes or more (at 0-1,000 feet elevation), the jars will be sterilized DURING processing in the canner. Therefore, when process times are 10 minutes or more at this elevation, pre-sterilization of jars is not needed. It doesn't hurt your product to do it anyway, but it does require additional time and energy and is unnecessary.
To pre-sterilize jars, place the cleaned jars right-side-up on a rack in a canner and fill the jars and canner with water to 1-inch above the tops of the jars. Bring the water to a boil and then boil for 10 minutes at elevations less than 1,000 feet elevation. Add 1 additional minute for each additional 1,000 feet of elevation. When you are ready to fill the jars, remove the jars one at a time, carefully emptying the water from them back into the canner. This will keep the hot water in the canner for processing filled jars.
Sometimes people choose to increase a 5-minute process time (at 0-1,000 feet elevation) for certain jams and jellies to 10 minutes so that they do not have to pre-sterilize the jars. The extra process time is not harmful to most gels and spoilage should not be an issue as long as the filled jars get a full 10-minute treatment in boiling water. (And remember your elevation adjustments to increase this process time as needed.)
In summary:
Is a 5-minute process time enough to sterilize jars? No. If you are using a process time of only 5 minutes, such as for some jellied products, then you need to pre-sterilize jars before filling them (or increase the process time to the equivalent of 10 minutes at 0-1,000 ft elevation).
If a process time is 10 minutes or more then will the jars be sterilized? Yes, if you are at 0-1,000 feet elevation, but be sure to wash and rinse them well, and keep warm, before filling them with food. If you are processing above 1,000 feet elevation, then you need to consider the elevation adjustments needed to sterilize jars so you use the equivalent to 10 minutes of boiling at 0-1,000 feet elevation.
Revised August 2023 National Center for Home Food Preservation
Newsflash
Green Beans and Botulism
How can I can my green beans safely?
Easy to grow in a home garden and delicious year-round, green beans are a popular home-canned food. Just like with any other home-canned food, it is important to always use proper procedures and follow tested recommendations. Yet we have received many concerns about canning green beans this season, including confessions of improper processing. Unfortunately, in multiple situations we’ve had to recommend discarding entire batches due to under-processing, because there is a risk of botulism from under-processed green beans. Botulism is a potentially deadly food poisoning.
To help you prevent waste, sickness, or worse, here are our responses to the most common questions about canning green beans:
Q: I want to can my green beans in a boiling water bath…is that ok?
No. Green beans are a low-acid food and require the higher temperature from a pressure canning process for a pre-determined length of time in order to destroy the potentially deadly bacterial spores of Clostridium botulinum, unless they are adequately pickled. The ONLY processing we can support for non-pickled green beans is under pressure, using the directions and steps found on our website at Canning Green Beans. The correct procedures include the steps for managing the canning process found here: Using Pressure Canners.
Q: My neighbor gave me green beans that were canned using the oven method…is it safe for me to eat them?
A: No. Using the oven method is NOT a recommended method of canning for green beans or any other food. It is dangerous because dry heat is slow to penetrate into jars (so recommended process times would not be enough), temperatures inside ovens vary (so a standard process time would be indeterminable), and no reliable, research-based safe process times have been developed for oven canning. There are also stories that jars heated in a dry oven could explode or break more easily than with recommended canning procedures.
Q: Last month I force cooled the pressure canner with my last batch of green beans, but now I think that may not have been a good idea…what should I do?
A: We recommend that the jars of beans be discarded. This is the safest option when home-canned foods are suspected of being spoiled or improperly canned. The cool-down time of a pressure canning process is calculated into the overall heat treatment required to destroy dangerous bacteria (Clostridium botulinum). So, if you do not let pressure canners cool down naturally and slowly to 0 pounds pressure, the jars did not receive a complete canning process. These jars are therefore considered to be under-processed, which means it is not safe to store them at room temperature. If it had been less than 24 hours, you could have refrigerated the jars immediately and eaten them within one week or frozen the green beans for longer term storage. Instructions for discarding suspect jars or detoxifying and cleaning unsealed spoiled jars are available on our website: Identifying and Handling Spoiled Canned Food .
Q: Last night I pressure canned my green beans using USDA recommendations, but this morning I noticed that 3 of the jars did not seal…can I re-process them?
A: Yes, if the jars received a proper pressure canning process but simply did not vacuum seal, then you can re-process them within 24 hours. Remove the unsealed lids and check the jars for nicks. Replace the jar if needed, and replace the lid with a new, properly prepared lid. Repeat the canning process, using the same processing time for this second process. Another option is to refrigerate the jars and eat the beans within a week, or to freeze the green beans for longer term storage. If more than 24 hours had passed, then we would recommend that you discard the beans.
Revised August 2020 National Center for Home Food Preservation
Newsflash
Canning Your Own Salsa Recipe
Can I can my own salsa recipe?
1. Salsas typically are mixtures of acid and low-acid ingredients; they are an example of an acidified food and appropriate for boiling water canning if the final pH of all components is less than 4.6. If the mixture has less acidity, it would need to be treated as a low-acid canned food and require sufficient research to eliminate a botulism risk as a canned food. If it is acid enough for boiling water canning, the actual proportions of ingredients and preparation method will help determine what the canning process time should be. So there is no way to tell someone how to can a homemade salsa without having detailed knowledge of the recipe, procedures used in preparation, and acidity and consistency of the final product. The proportions of your tomatoes, peppers, herbs and other vegetables will greatly influence what the safe canning process should be.
Summary, for all home canned foods: For home canning recipes, the specific recipe, and usually the preparation method, will determine how the product (salsa, in this case) can be processed--whether in a boiling water canner (BWC) or a pressure canner (PC). A Boiling Water Canner can be used for acid and properly acidified foods, while a Pressure Canner is used for low-acid foods. Then, the process time in the canner will be dependent on the specific recipe and product characteristics.
The Backgrounder on Heat Processing of Home-Canned Foods will explain some of the science behind the development of home-canning recipe, especially for low-acid foods or mixtures.
It explains why it is not always possible to home can foods like those that are commercially available/store-bought, or your own recipes.
2. Our USDA and Cooperative Extension recipes and processes for home canning are all tried and tested, and processing times decided upon for the recipe as provided and tested. We only recommend recipes and procedures we know to be safe, and encourage consumers to use tested, science-based home-canning recipes from reliable sources like our website or some equipment or home preserving ingredient manufacturers. Our recommended home canning recipes for salsa, as well as a discussion of how ingredients impact safety, are collected in the Sensational Salsas publication. We also have individual recipes with links to background information
The most flexible procedure we offer for a home-canned salsa is our Choice Salsa.
3. Someone new to canning or who has not read general canning principles should start with those principles: General Canning Principles
and know how canners are meant to be used, whether for boiling water or pressure canned products:
4. At this time, we can only recommend tested recipes as safe for boiling water canning, and we ourselves do not offer a pressure-canning process for a low-acid salsa. There is a Mexican tomato sauce that is less acid and pressure canned only, but it is not a chunky salsa; it is more sauce-like. Mexican tomate sauce.
The rest of our recipes noted as salsas have enough acid in them to make them safe from botulism when canned at boiling water temperatures only.
5. Your recipe could be frozen for long-term storage, but you will need to determine if you like the texture and flavor after freezing and thawing; there most likely will be changes in both texture and seasoning. I would try a small batch the first time for freezing. Many times herbs and spices are better tasting when added fresh after freezing and thawing, at serving time.
6. Please do not experiment with canning your own recipe that mixes low-acid vegetables together, even with “some” acid like vinegar or lime juice. If done improperly, you put yourself at risk for botulism, a potentially fatal food poisoning. This page has more on botulism and canned foods, as well as a section on the importance of food acidity and canning methods.
7. If you want to explore private testing of your recipe for canning, it most likely will require an investment through private companies. You could contact your local Cooperative Extension office to see IF they have names of testing companies in your state, and/or if they could contact the Food Science Department at their state land-grant university to obtain help.
8. The University of Georgia sells a book of all types of home food preservation recommendations (not just canning), described at https://setp.uga.edu.
Revised May 1, 2019 National Center for Home Food Preservation
Newsflash
Canning on Smooth Cooktops
Can I can on my smooth cooktop?
We have to say to follow manufacturer's advice because styles of smooth cooktops being manufactured differ in ways that influence suitability for canning. Some smooth cooktop manufacturers say do not can on them, while others who say it is okay still put stipulations on the diameter of the canner compared to the diameter of the burner. Boiling water or pressure canners may not be available that meet the maximum diameter pot they allow. There are several issues:
1. There can be damage to the cooktop from the excessive heat that reflects back down on the surface, especially if the canners used are too large of a diameter than is intended for the burner being used. The damage can range from discoloration of white tops to actual burner damage to cracking of the glass tops to fusion of the metal to the glass top.
And by the way, even if a manufacturer says a burner/cooktop can be used for canning, people should also be aware the scratching can occur if the aluminum canner is slid or pulled across the cooktop. This often happens with large, heavy filled canners, so people need to be careful.
2. Many of these cooktops have automatic cut-offs on their burners when heat gets excessive. If that option is built in, and the burner under a canner shuts off during the process time, then the product will be underprocessed and cannot be salvaged as a canned food. The process time must be continuous at the intended temperature, or microorganisms may survive. Also, if the pressure drops quickly, most likely liquid and maybe even food will be lost from the jar (it will spill over from the area of higher pressure inside the jar to the lower pressure now in the canner around the jar).
3. Even if boiling water canning is approved by the manufacturer, it may be necessary to fashion your own canner out of a flat-bottomed stockpot with a bottom rack inserted. Many canners do not have flat enough bottoms to work well on a smooth cooktop to be able to maintain a full boil over the tops of the jars. The pot used as a canner must also be large enough to have lots of water boiling freely around the jars, and at least 1 inch over the tops of jars. If the canner is too small, then it starts boiling faster than expected and the total required heat the jars receive in the canner even before the process time begins can be too short.
4. Some manufacturers of pressure canners do not recommend using them on a smooth cooktop. Follow the advice of your canner manufacturer.
Our recommendation, therefore, is to contact or consult information from the manufacturer of your smooth cooktop and your pressure canner, if interested in pressure canning, before making your decision to can (or not) on it. They are the recommended sources of this information and may also have up-to-date alternatives or suggestions for equipment that you can use. We also caution that you might have to be sure they understand how large your boiling water or pressure canner is, how long it must be heated at high heat, how long the hot canner may stay on the burner until it cools after the process time, and that the canner is made from aluminum (if it is).
Reviewed February 27, 2018
National Center for Home Food Preservation
SO EASY TO PRESERVE
The University of Georgia Cooperative Extension has now published a 6th edition of its popular book, So Easy To Preserve. The book was reviewed and updated in 2020. Chapters in the 388-page book include Preserving Food, Canning, Pickled Products, Sweet Spreads and Syrups, Freezing and Drying.