How to sterilize jars

How to sterilize jars

If you’re making your own preserves, jam or pickles you need sterilized jars to protect the food from bacteria, yeast and fungi. Traditional sterilization is quite time-consuming, but fortunately there are several simple methods of to achieve the same result.

Traditional sterilization

The traditional method is to put the pre-washed bottles & jars in boiling water for 15 minutes (and the lids for 5 minutes). It is important that the water fully covers the bottles. The disadvantage of this method is that often chalkiness (calcium carbonate) is formed on the surface of the glass – primarily caused by hard water. Furthermore, the jars must be removed from the hot water with (sterilized) tongs and it requires a bit of skill, experience and patience.

Modern sterilization

The following modern methods are more simple and just as effective:

  • In the oven: preheat the oven to 110-160°C. Wash the jars and lids in warm, soapy water, then rinse well and drain. Place the jars on a baking tray, the lids on another tray (the tops should be downwards). Put the trays in the oven for 10-15 minutes. When the bottles are dry then they’re done, so you can turn off the oven. If the lids have rubber seals, those have to be boiled, because dry heat damages them.
  • In the dishwasher: wash & rinse the jars then place them (mouths facing downwards) into an empty, clean dishwasher and turn on the drying program. The steam will sterilize the jars.
  • In the microwave: wash & rinse the jars then place them wet in the microwave, set it to run for 1 minute.
  • In a steam sterilizer: baby sterilizers (electric and microwave) are suitable for smaller jars. Put the washed jars on the lower rack (facing downwards), and the lids on the upper tack (facing downwards)! Always follow the instructions for the particular device!
  • In a pressure cooker: Put about 3 cm (an inch or so) in the bottom of the cooker. Tighten the lids onto the cleaned jars but then loosen them enough to allow the steam in. Following the instructions for your pressure cooker, bring up to pressure for 10 minutes. Use oven gloves to take them out when ready for use.
  • With sterilizing tablets: these are normally used to sterilize baby bottles and pacifiers but can be used for jars too. Just follow the instructions on the packaging! Warning: this method is done in cold water, so it’s only suitable for some pickles or foods preserved in oil or salt.

Tips

  • You can recycle shop-bought jars of jam & honey – but try to remove the labels by soaking them in warm water. Wash the jars thoroughly! Pay attention especially to the caps and lids – if damaged, get new ones!
  • If sterilizing in the oven, make sure that the oven is not be than 180°C because the glass may crack! In most recipes the jars must be warm before filling them. So leave the jars in the oven/dishwasher/sterilizer until you’re ready to fill them and take the jars out one at a time. Alternatively, for cold preserves (such as pickles and relishes), make sure the jars are totally cool – germs love lukewarm temperatures the most!
  • Don’t place the hot jars onto a cold surface – such as a marble – or use them in cold temperatures.
  • Don’t touch the inside of the jars and lids with your hands or anything that’s not completely clean.
  • Everything you use to fill the jars must be sterile! When you fill the jars be careful that the content does not come into contact with the rim of the jars (to avoid mould). It’s best to use a special jam funnel, which has a wide neck.
  • Do not fill the jar completely – just up to the neck of the jar or a centimeter below it.
  • If accidentally a little jam or sauce drops on the rim of the jar, wipe it off with an ironed tea towel or paper kitchen towel. Pay careful attention to the screw top ridges!
  • Caps & lids – not all lidded jars are suitable for making preserves – for example instant coffee bottles and similar jars with plastic lids, because they are not completely airtight. Best are the metal lids, which can be screwed tightly to the glass. For chutney and pickles use only padded metal lids, otherwise the vinegar will have a chemical reaction with the metal (most lids are padded these days). Alternatively use a waxed disk over the surface to create a seal then add a lid (or secure a cellophane lid with an elastic band). After 24 hours, check on the lids – they should be slightly concave due to cooling contraction. If they are convex or bouncy when pressed, the lid is not closed properly – these jars must be chilled in the refrigerator and their content should be consumed within a week or so!

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