National Center for Home Food Preservation Guide
The National Center for Home Food Preservation (NCHFP) is a USDA-funded research center at the University of Georgia that publishes free, laboratory-tested guidelines for home canning, freezing, dehydrating, and fermenting. Its recommendations are the accepted scientific standard for home food preservation in the United States and are available at no cost at nchfp.uga.edu.
The center’s guidelines carry weight because the stakes in home food preservation are uneven. Freezing strawberries in a zip bag carries minimal food-safety risk. Pressure canning green beans at too low a temperature, or for too short a time, can allow Clostridium botulinum spores to survive inside a sealed jar. NCHFP-tested recipes specify jar size, headspace, pack style, and processing time because all four variables were measured during heat-penetration studies in a food laboratory. Change any one of them and the tested time no longer applies to what is actually in your jar.
What is the National Center for Home Food Preservation?
The NCHFP was established in 2000 through a cooperative agreement with the USDA National Institute of Food and Agriculture (NIFA), housed in the University of Georgia’s College of Family and Consumer Sciences. Its core function is translating food-science research into practical, tested recommendations that home preservers can apply without access to a laboratory.
Before the NCHFP consolidated federal guidance, relevant USDA bulletins were scattered across decades of documents, some of which pre-dated heat-penetration testing as a standard method. Open-kettle canning, which fills hot jars and relies on the food’s own temperature to create a seal, appeared in older materials without sufficient evidence of safety at home scale. The NCHFP reviewed the existing body of guidance, retired methods that lacked scientific support, and assembled one authoritative source. University extension services at land-grant universities across all 50 states now use NCHFP recommendations as their baseline.
The institutional backing matters for a practical reason: NCHFP processing times trace back to documented laboratory studies with instrumented jars and recorded temperature curves. That is a different foundation than a processing time inherited from a community cookbook or a method passed down through a family.
What does the NCHFP publish?
The flagship document is the USDA Complete Guide to Home Canning, a seven-guide set available as free PDFs from nchfp.uga.edu. The guides cover: principles and equipment, fruits and fruit products, tomatoes and tomato products, vegetables, poultry and meats and seafood, fermented and pickled vegetables, and jams and jellies. Each guide specifies tested processing times, jar sizes, headspace measurements, and where applicable, added-acid requirements.
Beyond canning, the center publishes:
- Freezing guides organized by food type, covering fruits, vegetables, meats, poultry, seafood, dairy, and prepared dishes, with pre-treatment recommendations for each
- Drying and dehydrating guides for fruits, vegetables, herbs, and meat jerky, including pre-treatment options such as sulfuring and ascorbic acid dips, and the internal temperature requirement of 160°F for meat jerky before or after drying
- Curing and smoking guidelines for meats and fish, specifying cure salt concentrations, brine ratios, and final internal temperature targets
- Salt-brine fermentation guides, primarily for sauerkraut and cucumber pickles, including salt-to-water ratios, expected fermentation timelines, and descriptions of what normal and spoiled ferments look like
- A searchable FAQ database and a collection of tested recipes for salsas, relishes, pie fillings, and other mixed products
A separate book titled “So Easy to Preserve” is published by the University of Georgia and sold through the university press. It covers the same methods as the website guides and adds additional tested recipes. It is not a free download.
Recipes labeled as “NCHFP-tested” were validated through heat-penetration laboratory studies. Recipes found on extension sites, in older canning books, or on cooking blogs are not uniformly at the same standard. Confirming the original source of any recipe before canning is a straightforward habit that takes less time than it saves.
NCHFP preservation methods at a glance
| Method | Suitable Foods | Key Safety Condition | Altitude Adjustment |
|---|---|---|---|
| Water bath canning | High-acid foods at pH 4.6 or lower: fruits, jams, jellies, pickles, tomatoes with added acid | 212°F (100°C) boiling water at sea level | Add processing minutes above 1,000 ft |
| Pressure canning | Low-acid foods: vegetables, meats, poultry, seafood, soups, mixed recipes | 240°F (116°C) at 10 lbs pressure at sea level | Increase gauge pressure above 1,000 ft |
| Freezing | Most foods; quality varies significantly by type | 0°F (-18°C) or below; blanch vegetables before freezing | Not applicable |
| Dehydrating | Fruits, vegetables, herbs, meat jerky | Meat jerky must reach 160°F internal before or after drying | Not applicable |
| Curing and smoking | Meats and fish | Verified cure salt concentration and final internal temperature | Not applicable |
| Salt-brine fermentation | Vegetables: sauerkraut, cucumber pickles, others | Correct salt-to-water ratio; pH lowered by natural fermentation | Not applicable |
Why do NCHFP processing times differ from older canning guides?
Heat-penetration testing is the basis for all NCHFP processing times. Researchers pack jars exactly as a recipe specifies, instrument the geometric center of the jar with a thermocouple (the coldest point in the jar during processing), and record how long that cold spot remains below the temperature needed to destroy botulinum spores. The published processing time is the time required at that cold spot, not the temperature reading in the surrounding water or steam.
This is why ingredient substitutions and jar size changes matter more than they appear to. Thickening a salsa by reducing liquid or adding more peppers changes the viscosity of the product, which slows heat penetration through the jar. Switching from the tested pint jars to quart jars moves the cold spot further from the jar wall. Using a tomato variety with higher water content changes the density. In each case, the published time was measured on a product that no longer matches what is in the jar.
Older USDA bulletins did not always specify tested pack styles, sometimes allowed open-kettle canning, and in some categories carried processing times that predated modern heat-penetration measurement. The NCHFP did not invent new preservation methods; it tested what had been assumed safe and published the results with enough specificity to be reproducible. That specificity is the functional difference between NCHFP guidance and older materials.
One detail that does not appear often in competitor articles: the NCHFP’s testing also establishes whether a given recipe is safe for both raw pack and hot pack styles, or only one. Raw pack and hot pack produce different starting temperatures and densities in the jar, which changes the heat curve. A tested time for hot pack salsa tomatoes is not automatically transferable to raw pack, and the guide specifies which pack style was tested.
How does NCHFP guidance handle tomatoes?
Tomatoes sit close to the pH 4.6 threshold. Modern hybrid varieties often measure closer to 4.6 than older heirloom types, and some fall above it, meaning they are not reliably high-acid on their own. The NCHFP updated its guidance to require added acid for water-bath-canned tomatoes: 1 tablespoon of bottled lemon juice or 1/4 teaspoon of citric acid per pint jar, scaled to 2 tablespoons or 1/2 teaspoon per quart. Bottled lemon juice is specified rather than fresh because fresh lemon juice has variable acidity that cannot be verified in a home kitchen.
Pre-2000 canning books may not include this requirement. If you are working from an older book, comparing the tomato sections against the current NCHFP site before each season is a practical step. The NCHFP site notes when its current guidance supersedes older recommendations and explains the reason for changes where relevant.
Do altitude adjustments apply to NCHFP recipes?
Yes, for both water bath and pressure canning. All NCHFP processing times are calibrated at or near sea level.
Water boils at lower temperatures at higher elevations. At 5,000 feet, water boils at approximately 202°F instead of 212°F, which means a water bath canner at that altitude delivers measurably less heat per minute. NCHFP tables specify additional processing minutes by altitude band: 1,001 to 3,000 feet, 3,001 to 6,000 feet, 6,001 to 8,000 feet, and above 8,000 feet. The adjustment depends on processing time as well as altitude, so the table values differ by recipe category.
For pressure canning, reduced atmospheric pressure at altitude means that 10 lbs of gauge pressure no longer corresponds to 240°F inside the canner. NCHFP tables specify increased gauge pressure for both dial-gauge and weighted-gauge canners at different altitude bands. Weighted-gauge canners typically shift from the 10-lb setting to the 15-lb setting above 1,000 feet. Dial-gauge canners require more granular adjustment and need to be tested for accuracy each season with the local extension office.
Can atmospheric steam canners substitute for a water bath canner?
The NCHFP evaluated atmospheric steam canners and concluded they are an acceptable substitute for water bath canning under two conditions: the food must be high-acid, and the processing time must be 45 minutes or less. The steam canner must be able to reach and sustain 212°F throughout the entire processing period. Not all atmospheric steam canners on the market meet that standard, so confirming a specific unit against NCHFP criteria before substituting is necessary.
Steam canners are not a substitute for pressure canning. The physics does not change with the type of canner: low-acid foods require internal temperatures above 212°F to destroy botulinum spores, and no atmospheric device reaches those temperatures. If a recipe calls for pressure canning, a pressure canner is the only safe equipment option.
Frequently asked questions
Is the NCHFP Complete Guide to Home Canning free to download?
Yes. All seven guides in the USDA Complete Guide to Home Canning are available as free PDF downloads at nchfp.uga.edu. The center also offers a printed version through the University of Georgia press at a nominal cost. The separate “So Easy to Preserve” book, which includes tested recipes and method explanations beyond what the free guides cover, is sold through the university and is not a free download.
What is the pH threshold that separates water bath canning from pressure canning?
The threshold is pH 4.6. Foods at or below that value are classified as high-acid and can be safely processed in a boiling water bath canner at sea level. Foods above pH 4.6 are low-acid and require pressure canning to reach the 240°F (116°C) temperature needed to destroy Clostridium botulinum spores. Tomatoes fall near this threshold and require bottled lemon juice or citric acid added per jar when processed in a water bath.
Does NCHFP guidance cover home fermentation?
Yes. The NCHFP publishes guidance on salt-brine fermentation for vegetables, covering sauerkraut, cucumber pickles, and similar products. Safety in fermentation depends on salt concentration adequate to suppress harmful bacteria while allowing beneficial lactobacillus organisms to lower the pH to a shelf-stable level. The fermentation section includes tested salt-to-water ratios, typical fermentation timelines by temperature, and descriptions of signs distinguishing a healthy ferment from one that should be discarded.
How often does the NCHFP update its recommendations?
The NCHFP updates guidance when new research supports a change, not on a fixed schedule. The added-acid requirement for tomatoes is one documented example; the center has also revised processing times for specific vegetables and clarified the conditions under which steam canners are acceptable as new studies have been completed. Guide pages on the website carry publication and revision dates. If you are working from a printed version of the USDA guides, checking the online version for any category you plan to preserve is a reasonable step, particularly for vegetables, meats, and mixed-ingredient recipes.
Bottom line
The NCHFP’s practical value is straightforward: it converts food-science laboratory results into specific numbers you can act on at home, including processing time, pressure setting, headspace, and added-acid amount. Using its tested recipes requires following those specifications as written, including jar size and ingredient ratios, because those details were part of the heat-penetration study. When a recipe cannot be found in the NCHFP guides, cooperative extension services at land-grant universities using the same testing methodology are the appropriate next resource. The full guide set is available free at nchfp.uga.edu.