"We eat what we can and freeze what we can, and what we can't, we can" is a saying in my family.
The USDA Complete Guide to Home Canning is the bible of safe canning. If it's done right, canned food can still be safe to eat after 100 years.
Io demonstrates at "Fort Awesome" in Berkeley CA. Other illustrations are from the USDA
Step 1: Why Canning?
This chart from the USDA shows why this is good advice. The microorganisms that cause food to spoil don't live well at high and low temperatures.
Canning is a way to preserve food at room temperature. It works by cooking the food and containers at high temperatures to kill micro-organisms and sealing the jar so no new ones can enter.
Properly canned food is safe. Improperly canned food can cause Botulism poisoning from Clostridium Botulinum bacteria. The name comes from the Latin word for "sausage", "botula".(wpedia)
The spores of this bacterium are present nearly everywhere. They can survive some boiling. They thrive in an anaerobic environment such as a sealed can, producing a nerve toxin. They can't handle acidity below ph4.6, oxygen, or a wet temperature above 250f.
The keys to safe canning of food are PH, moisture content, cooking temperature, pressure, time, sterile procedures and proper sealing.
Step 2: Get Too Much Food
That's a good choice because kiwi fruit is acidic. Sour = acidity = low ph. Clostridium Botulinum bacteria spores can't survive in sour food. Here's the approximate ph of a variety of foods.
Canning a big quantity takes just as much time as canning a little bit. So make a lot.
Correction: Io says her recipe says not to double the recipe or make larger batches, or it won't set up properly. In that case make multiple batches!
Step 3: The importance of "PH"
Acidic foods can be canned at boiling water temperatures.
Low-acid foods must either be pressure-canned, or acid must be added to lower the ph. Citric acid
(lemon juice), ascorbic acid (vitamin C), acetic acid or lactic acid vinegars are good choices of food acids that can lower the ph of the food.
Step 4: Cook It
Chant "Boil that dust speck! Boil that dust speck!" just like in the book "Horton Hears a Who" by Dr. Seuss, 1954.
Step 5: You'll Have Company
Step 6: Sterilize the Jars and Lids
When you get them they're clean but not sterile. Make sure they're fully submerged under the water. Boil them for 10 minutes if you're at sea level, and one minute for each 1000 feet of elevation above sea level.
Step 7: Altitude and Boiling Temperature
You'll definitely need a pressure canner to get your water hot enough to sterilize your jars.
Step 8: Fill The Jars
If any gets on the lip of the jar wipe it off carefully so the lid will seal well.
Leave a little bit of an air gap at the top.
When the air cools off later, it will contract making a vacuum.
That will make the lid go "ping" and suck inward.
Later on when you open the jar, you'll check that the lid is still sucked down. When you open the lid, hear the air suck in as the lid pings up. That's the sound safe canned food makes.
If that doesn't happen it means it wasn't sealed properly. Be afraid.
If the lid is bulged up, you're in trouble.
You've maybe got a witch's brew of festering botulism in there. Throw it away.
Step 9: Ladles and Funnels
Step 10: Boil the Filled Jars
Boil them for the right number of minutes.
What is the right number of minutes? Refer to the USDA manual or a trustworthy recipe. Usually it's 15 or 30 minutes.
VA ag extension recommends these boil times:
Processing Times For High-Acid Foods Using A Boiling Water Bath Canner (212° F):
Fruits & Vegetables Pints Quarts
Apples (hot pack)*** 20 minutes 20 minutes
Apricots (raw pack)*** 25 30
Berries (raw pack) 15 20
Cherries (raw pack) 20 25
Dill Pickles (raw pack) 10 15
Sweet Pickles (raw pack) 10 15
Fruit Juices (hot pack) 15 15
Fruit Jams and Jellies 10 10
Peaches (hot pack) 20 25
Pears (hot pack) 20 25
Plums (hot pack) 20 25
Pickle Relish (hot pack) 10 --
Rhubarb (hot pack) 10 10
Tomatoes (hot pack)**** 35 45
Tomato Juice (hot pack)**** 35 40
Step 11: Canned!
For more details about canning technique, read the rest of the USDA Manual