What Exactly Is Canning And How Is It Different From Making Preserves?

Canning is rewarding and economical, it saves freezer space and cost, preserves food for longer and uses far less sugar and makes sharing produce easy.  Read on to learn more.

Canning (also known as 'bottling')

Canning is the storage of all manner of cooked and raw produce in glass jars or tins.  This is the process that the food manufacturing industry uses and it can be replicated on a small scale at home.  Indeed, canning in jars - which has long been a very popular activity in the U.S.A - is fast becoming popular in this country too. 

The Water Bath Method

There are two approaches to canning, each appropriate for different foods.  High acid content foods such as fruits and tomatoes are suitable for the simple 'water bath' method.  This method is generally thought to be the place to start when setting out on canning at home.  Fruits and tomatoes can be preserved raw, suspended in a light syrup (beautifully preserving their flavour) or cooked via a recipe into a sauce, pie filling, jam, chutney or pickle.  The thing to remember is that high acidity means bacteria find it harder to grow and are destroyed more easily at lower temperatures when heated.  High acidity foods also set more easily to become conserves.  These two benefits of acidity are why so many recipes we use include lemon juice and why pickles and chutneys use vinegar to safely preserve low acidity vegetables.

So, the waterbath method involves peeling, briefly cooking the fruit and decanting it  into still warm sterilised jars.  Instead of adding sugar and bringing your fruit to a rapid boil, as you would do for jam making, you are decanting sliced fruit segments straight into the jars and adding a pre-boiled light juice, syrup or water into which the fruit will be suspended.

This process is known as 'hot packing' and is useful for several reasons.  It means the fruit will have shrunk and therefore is less likely to float in the jars.  It means oxygen trapped inside the fruit will have dispersed and the heat from the cooked fruit will mean the seal on the jars is really good and the shelf life is therefore extended.

Having decanted fruit into the jars, leaving the correct headroom for your recipe and not over tightening the lids, you are then submerging the jars into a large pan of boiling water for the stipulated time.  The process is exactly the same for sauces, jams and pickles - only the recipes vary.  You can buy a special water bath pan and rack quite reasonably, or use your own deep pan.

The Pressure Cooking Method

This method is for low acidity foods and must be done using a special pressure canning machine.  Although, the machine is expensive it does open up a whole world of preserving raw and cooked meats, vegetables, soups, stews and much more.  Low acidity foods require a period of heating at 240⁰F/115⁰C, this ensures that all microorganisms are destroyed.  A meal in a jar is there on a larder shelf.  The internet is absolutely stuffed with recipes for canning fruit and tomatoes using the water bath method.

Lids Explained

Jars suitable for canning all use a special two part self-sealing lid. This is key.  The disc section has a special compound around its inside circumference.  Before bathing or steaming your jars, the disc is placed on top of the clean jar opening and  is held in place by the screw band section.  In both methods, the screw bands should just be tightened firmly but not with your full strength before processing, allowing any remaining air to escape.

Once out of the water the lid will be progressively pulled tighter and tighter as the produce cools and the compound forms an airtight seal.  After the jars are cool the lid should just be left and not re-tightened.  You will hear a popping sound as the contents cool, this is the suction occurring.  You will see the lid has a slight dip in the middle, so you can rest assured the seal is good and can check this periodically over time.  Good Luck!

The Right Jars

We recommend Mason Jars ( similar to the U.S 'Ball' Jar), Familia Wiss Terrines and Kilner Jars for canning.  All are made from  good quality tempered glass and are complete with their two part lids.  Spare discs can also be bought for repeated jar use over the years.  Please click here for our full range of jars.