How To Preserve Acidic Foods

Making your own preserves can be both rewarding and fun. Doubly rewarding, really, because if you buy your produce in season, it is generally much cheaper than buying a pre-preserved version later on.

Example: I paid $5 for 1.8 kg/4 lb of strawberries and ended up with 10 half pint/240 ml jars of jam… Each jar was about 50 cents but they can also be re-used. $10 for ten jars of jam? Yes please! And what’s better is you can dictate how much sugar, if any, that you add.

How you handle the preserving of different foods depends on their acidity, which helps to protect them from developing bacteria:

  • Acidic foods, like tomatoes and strawberries, need to be “processed” (boiled) for 10-15 minutes and then left to cool completely over night.
  • Non-acidic foods must be pressure-canned to really super-heat the contents of the jar and thoroughly eliminate any nasties that might be present because they don’t have the innate defense of acidic foods. I will go into more detail on non-acidic foods here.

The following will outline the steps required to safely preserve acidic foods, which if followed correctly should be safe for up to 12 months. However, be smart about it. If, in a few months time you open the jar and it looks/smells off – don’t eat it.

How to Preserve Acidic Foods

Equipment required:

  • Canning jars and lids
  • Ingredients
  • Large saucepan, small saucepan, pot to prepare filling
  • Wide-mouthed funnel
  • Non-metal spatula
  • Jar tongs
  • Jar wrench
  • Magnet
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Jar tongs, tongs, wrench, magnet, spatula with incremental measurements, wide-mouthed funnel

Place jars in a large saucepan with a stand in the bottom (to keep them raised off the base) and fill with water so that they are immersed. Bring to the boil and then reduce to a simmer to await whatever filling you are preserving.

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Place the lids in a separate saucepan and simmer. This will both sterilise them and soften the sealant that is around the rim. If you are using store bought canning jars that come with lids and rings, you only need to sterilise the lids, not the rings.

Prepare your filling; examples include strawberry jam, raspberry puree, cranberry sauce or tomato puree/sauce. Make sure you keep it hot.

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Using the jar tongs and wrench to manipulate the hot glassware, remove each jar from the boiling water and empty it. Fill each jar using the wide-mouthed funnel, leaving 2 cm between the filling and the mouth of the jar. Sterilise the spatula for 2 minutes in boiling water, then use it to remove any air bubbles from the jars by scraping the inside edges.

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Wipe the jar rim and place on the lid, then the ring and tighten – only use your hands to do this, do not over-tighten the ring with any implement.

Replace the jars in the simmering water, ensuring they are fully submerged by about 4-5 cm. Bring to the boil and process for 10-15 minutes to kill off any remaining bacteria that might be present.

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More water must be added to submerge these jars before processing

Let the water stop boiling and the jars sit for 10 minutes further to let the glass cool slowly, then use the jar tongs to remove each jar and place them on a cooling rack. Dry the metal lids/rings to prevent rust and leave them to sit for 12 hours at least. After this time, test each seal with the magnet; if it pops up then either re-process or refrigerate/freeze the jar immediately. Refrigerated jars should be used within 2-3 weeks of opening.

* There is nothing preventing you being doubly certain about killing bacteria and pressure-canning acidic foods instead of water-bath canning them – you can do this, but the colours will not be as bright in the end.

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