The Power Went Out During Pressure Canning: What to Do With the Batch

The steps below are about staying safe around the pot, then deciding what to do with the food.

What do you do in the first few minutes?

1. Leave the lid on

   University of Georgia Extension says not to force a lid open if the cover lock hasn't released. Presto says never to open its digital canners until all pressure is gone and the vent and cover lock has dropped.

2. Do not cool it yourself

   The USDA says not to force-cool a canner. Cold water, or opening the vent early, can cost you liquid and seals. It may lead to unsafe food or spoilage.

3. Leave it where it is

   University of Georgia Extension says it's fine to leave a canner in place. That's better than letting jars tilt inside one that's too heavy to move easily. It also says a canner generally should not go on an outdoor LP gas burner, so moving it to one isn't the fix it may seem.

4. Write down what you know

   Note when the power went out, when timing began, and anything the display showed. You'll want this when you decide, or when you call someone.

What do the sources say about the batch?

We looked for a statement written for exactly this, and found few. Here is what exists, by machine.

• Stovetop canner on an electric range: the USDA's rule applies once you have heat again. Bring it back to pressure and start the timing over, with the full original time. Kansas State says that if a burner shuts off during processing, food can be under-heated.
• Presto Precise: the manuals we read for the 02153 and 02154 and the 02144 have no section on power cuts. Their tables do say that if pressure is lost during the canning phase, the process isn't complete and the food must be reprocessed in full. See Presto's error codes. Call 1-800-877-0441.
• NESCO NPC-9: the guide we read has no section on power cuts. NESCO's customer service is at 1-800-288-4545.

Presto's FAQ says its canner stops the process and shows a code if the temperature falls below 240°F. It doesn't say what happens after a power cut. So we don't know whether a plug-in machine picks up where it left off, starts over or stops for good when the power returns. We'd rather say so than guess. A machine that restarts hasn't told you the food got the heat it needed.

The NESCO NPC-9 is a cooker-canner combo. Penn State says these can't be recommended because research on their safety is missing. It names no brand. Putting the NPC-9 in that group is our own reading. See are electric pressure canners safe.

Doesn't the cooling heat make up for it?

The National Center for Home Food Preservation (the US canning experts at the University of Georgia, "the National Center" from here on) does say that heat from coming up to pressure and from cooling counts toward the total. It says this about how USDA instructions work in full-size canners. It does not say it about a run that was cut short. No source we read offers a way to work out what a shortened run delivered.

So a sealed lid doesn't settle it. A seal does not show that the food got the heat it needed. Never taste a suspect jar, because spoiled low-acid food may show little or no sign. The CDC says home-canned vegetables are the most common cause of botulism outbreaks in the US. The botulism page explains why this matters so much for low-acid foods (vegetables, meat, chicken, fish).

What if the power stays off?

The sources are thin here, and they differ. We report them and give no verdict of our own.

• Ask Extension expert, answering someone who stopped a canner early: gives a 24-hour window. Within it, the jars must get the full time again. Sealed jars count as unsafe if they didn't get the right time. Food that wasn't properly processed or reprocessed should be thrown out.
• Another Ask Extension expert, answering someone whose jars sat in a switched-off canner for days after an evacuation: says to throw the food out, and not to feed it to animals.
• Nebraska Extension: allows 24 hours for correctly processed jars that did not seal. Where safe methods weren't followed, such as a wrong time, it allows 2 hours to re-can.
• The National Center and the USDA: their 24-hour window is written for lids that failed to seal, not for an interrupted process. The National Center adds that the first try must have used a tested recipe. With no tested hot-pack recipe, the product may not be safely reprocessed.

Ask Extension answers are individual experts, not positions of a school. If you're unsure, call your county extension office (free local food-safety advice). It's worth doing while the clock is still running.

How do you reprocess?

Presto's manual describes it this way for a jar that needs reprocessing. Take off the lids, reheat the food, use the hot pack method, pack into clean, heated jars, use new lids, and reprocess for the full recommended time. Take the details from your tested recipe. Quality will suffer, and some foods may have no hot-pack process at all. Tested recipes and your canner's manual are the places to look. The notes on jars that did not seal may help too.

What if outages are common where you live?

A plug-in canner stops heating when the power goes, and so does a stovetop canner on an electric range. A gas range may be different, but that depends on your range, so read its manual. We read nothing on running one through an outage. Our electric vs. stovetop comparison covers the wider trade-offs.

For the normal order of steps, see how to use a pressure canner.