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How to Preserve by Heat Processing

15 Mar
Heat processing is a form of preserving foods by putting hot, warm or cold foods into a container and heating until any bacteria that might be within the food or container is killed and a vacum is achieved. It is a very useful technique for the kitchen gardener, no glut of produce need ever go to waste and can be stored for times when there are less fruit and vegetables available fresh from the garden or market.
The simplest way to achieve this on a domestic scale is to use glass jars, with lids and heat the jars and their contents in boiling water, the ‘hot bath method’.
Preparing the food
Food can be processed from cold or hot. I only use the hot method, cooking the fruit of vegetables before bottling, as this is the most reliable way to ensure food does not spoil and can be stored safely.
You need to use jars that can be heat processed such as; ‘mason’ jars which come with a two piece lid, a domed cap that fits tightly on the neck of the jar and a screwband which fits over the cap and is screwed down onto the jar, kilner type jars which have a clamp down glass lid sealed with a rubber ring, or simple glass jars with special lids. I buy 250g jars from our local agricultural store that sell different types of lids including those for heat processing. The jars can be re-used as many times as they remain sound. Jars must be scrupulously clean and without any flaws, cracks or chips as any flaw could result in the galss shattering while being heated.
The lids are the important bit, when heat processing the lids need to allow for the expansion of air and liquids and then the function to tighten or lock to seal and make a vacum.  The basic lids are those with a circular dimple which become depressed during the process indicating that a vacuum has been achieved. There are also 2 part lids and clamp lids. It is essential to purchase new lids or seals for each use.
Filling Jars
Pour the hot food e.g. tomato sauce, passata, salsa, cherry compot whatever it is into the prepared jars, leaving a 1cm gap at the top, screw the lids on well but not too tight.

There are special heat processing pans available but I find using a pasta pan with a draining insert works just as well particularly if  I am only processing small batches. The pan I have was not expensive, I bought it in Ikea at least 10 years ago, and it will fit 5 x 250g jars comfortably.
Carefully place the jars in a single layer around the sieve part of the pan then lower into the outer pan. Fill with hot water to 2 inches bellow the lids, and bring to the boil. Once boiling cover with a well fitting lid and set a timer for 15-20 minutes. When the timer goes off raise the draining insert and set down with the jars inside. Use a towl to protect your hands from the heat, tighten all the jars. If used kilner type jars adjust to final lock down position. Set aside to cool. The airlocks in the lids should all depress as they cool which indicates a full seal. If any do not depress repeat the process.
Label and store the jars in a cool dark place. They will keep for several years
If dimples in the lids rise again this is a sign that air has entered the jar and the food may have spoiled. Do not consume as there could be a risk of botulism.
Note Make sure you follow the instructions that come with the type of jars you have purchased, as each jar type will have its own sealing mechanism.


Chilli Paste (Harissa)

28 Sep

This is a thick sauce type of harissa, the kind you can serve with everything, even spread it on bread. It is  hot, but not REALLY hot, made with fleshy red peppers and chillis. I came up with this Harissa because our friend Graham, who came over here a few summers ago, wanted to know if I had a recipe for the harissa we all ate one morning at a local market because he’d been dreaming of it and wanted to make some back home in Australia. So I started experimenting and came up with this which I think, is even better than the one we ate in the market.

  • 500g red pepper puree (fresh peppers ground and sieved)
  • 3-5 fresh hot red chillis (to taste)
  • 4 garlic cloves, crushed
  • 2 tsp coarse sea salt
  • 2 tsp cumin seeds
  • 1 tsp caraway
  • 1 tsp fennel seeds
  • 2 tbsp dried mint leaves, crumbled finely

Make the puree
To make red pepper puree choose thick fleshed peppers; sweet, hot and medium heat if you can, to give a more complex flavour. Wash the peppers, cut in half and remove the seeds and stalks. Put the peppers in a food processor and grind to a paste. Put the paste in a pan and cook for 15 minutes or so. Leave to cool. Press the pepper paste through a sieve, or use a vegetable mouli, to make a smooth paste and to get rid of the skins and any loose seeds.

After sieving I ended up with about 500g of pure pepper puree, which I put back into a clean pan. Dry roast the cumin and caraway, cool and grind with the fennel to a powder. Add the spice powder along with the remaining ingredients and cook until the mixture thickens. Pour into sterilized jars and seal. For storage; heat process the jars in a water bath, for 20 minutes. It should keep for a year or more. If you don’t want to keep it that long it will store in the fridge, for a month or more, in a clean jar, topped with oil to exclude air.
Note on the Heat
I used a mixture of sweet peppers and medium heat paprika peppers; Doux D’Espagne, Nardello, Paprika, Pimento de Barcelona, Pepperoncini, Buran, Satans Kiss and Anatohl. If you use only sweet peppers for the paste add more chilli peppers to increase the heat to taste. For the hot peppers I used cayennes & jalapenos .
Note on Texture
If you don’t want to go to the bother of sieving the pepper paste and don’t mind eating the skins by all means leave this step out. I had to do it because one variety of paprika peppers I grew had such tough skins they really indigestible and little bits can get stuck in your throat.

This recipe was originally posted on  13/10/2008

Passata (Tomato Paste)

28 Sep

Of all my kitchen garden preserves passata, or sieved tomatoes, is one of the most useful. I grow large numbers of tomatoes just so that I can bottle them for use all through the year. There are two ways to make passata and I thought I’d write about them here.

There are 3 Steps to making passata 

1. Clean and prepare tomatoes

2. Cook

3. Sieve or pass through a passata machine


Wash the tomatoes, cut off any bruises or bad bits and cut in half or into rough chunks.

Boiling  Simply put tomatoes into a large pan with 1 tsp of salt per 500g and bring to the boil, simmer until the tomatoes are soft, about 15-30mins.

Baking Baking the tomatoes adds a deeper, sweeter flavour and reduces the liquid which makes a thicker stronger tasting passata. This is the best method for poorer flavoured tomatoes or those that are a little too watery. Cut the tomatoes in half and spread out on a large baking tray season generously well with sea salt and bake in a low oven for 1 hour.


There is a special machine for processing tomatoes to remove the skins and seeds called a passata machine.  I got myself one last year from Seeds of Italy and it really does make the job easier, particularly if you are processing large quantities.

Other wise you can use a sieve, a spoon and some elbow grease. Spoon batches of cooked tomatoes into the sieve, stir and press with the back of a spoon to push the pulp through the sieve, leaving the skin and seeds behind.


The passata is now ready to use or preserve. My prefered method is to bottle while hot and heat process.

See How to Preserve by Heat Processing

If you don’t want to heat process you can also freeze the sieved paste in cartons or bags instead. I don’t do much of this anymore after an accident with our electricity supply and our freezer and I lost the entire years harvest. The old method of bottling and heat processing just seems more reliable to me.

See How to Preserve Tomatoes for other ways of preserving tomatoes. 

Preserving Tomatoes

28 Aug

Tomatoes make some of the most valuable preserves and condiments for the pantry; sun dried tomatoes, passata, tomato concentrate, sauces or salsas, and chutneys. Processing tomatoes for preserving can be a messy time consuming affair and the kitchen can look like a set for the chainsaw massacre but for me the rewards are worth it, It is such a luxury to have all this lush tomato stuff in the cupboards because lets face it we won’t be seeing tomatoes again until next July unless I can get some to ripen a little earlier next year. Each year I grow more and more tomatoes so that we will have enough to preserve. We eat so much of these tomato preserves that there is just never seems to enough until next years crop.

The all purpose preserve is the basic sieved tomato sauce called Passata, to take the Italian name for it, just tomatoes boiled with a little salt and then sieved or put through a pasta machine. It is indispensable in the kitchen as a base for all kinds of dishes. For full instructions on making passata see How to Make Passata.


It has more body than sieved tomatoes and very useful pantry preserve. The process is slightly different from passata in that the tomatoes are skinned and de-seeded then chopped.  This is the basic stuff I have left over from seed saving and as a seed saver for Association Kokoplelli I tend to produce a lot of this. It can be used fresh in its basic state, frozen as is or bottled cold and heat processed. I usually cook it to reduce the amount of liquid in the pulp before bottling into 250g jars with a sterilising lid and heat process for 20 minutes.

Many sauces that we regularly make can be heat processed. Tomato sauce differs from passata in that the tomatoes are cooked with other ingredients and it is not sieved so it has more body and is perfect to use straight from the jar on pasta or in other dishes that require a tomato sauce. See my Basic Tomato Sauce recipe.

Drying tomatoes is like alchemy the fruit wither down but their flavour just gets bigger and more intense. It is best to use a fairly dry type of tomato or the drying process will take forever. A good tip is to place the tomatoes on a metal surface as the heat reflects back and speeds the drying process up.


This is the cheapest method of drying tomatoes requiring no real apparatus but it does require sunshine. Slice plum tomatoes length ways, remove the green pithy stem sprinkle with salt and lay cut side up on a slatted tray or basket. Cover the tray with netting or gauze to keep insects out. Position the tray in the sun during dry sunny days and bring indoors when the sun goes down. If the weather is at all damp bring the tray indoors and sit on a sunny window still making sure there is plenty of ventilation. It takes about 3 days but could take a little longer depending on the weather and how dry you want the tomatoes. Dust off the salt and store packed into sterilised air tight glass jars in a cool dark place.

Follow the same method as above but place the cut tomatoes on a large oven tray and place at the bottom of an oven set low. I normally set our oven between 50c and let them ‘dry’ for anything up to 24hrs. The length of drying time will depend on: the type of tomatoes, your oven and how soft you want to have the tomatoes.

I use usually use San Marzano plum tomatoes for this recipe. Follow the oven drying method as above but you want the tomatoes to be slightly soft, in our oven 50-75c for 6-8 hours works. Dust off any excess salt and pack into hot sterilised glass jars. Cover with olive oil to 1 cm above the tomatoes, tap gently to knock out any air and seal immediately. Store in a cool dark place. These make wonderful hors d’oevres or tapas straight from the jar and a real treat in winter.

I tried freezing tomatoes after reading Susan’s post on Farmgirl Fair Preserving the Harvest: How to Freeze tomatoes the really easy way. It sounds too simple to be true but often the most simple things are the best. All you do is wash the tomatoes, chuck them in a bag then put them in the freezer. Done! Great tip- Susan thanks.

This is the most complicated and time consuming of the tomato preserves. Concentrate is basically passata reduced down to become a thick paste with a very concentrated flavour. It takes a lot of tomatoes to make a small jar of paste but if you like tomatoes it is worth it. I could eat this stuff just spread on bread.
To Make roughly chop ripe tomatoes, cutting off any bad bits, and chuck them into a large pan. Season well with sea salt and cook over a low heat for 20-40 minutes giving it a good stir every now and then so that it does not stick. The tomatoes should disintegrate and become pulpy. Cook for longer if not. Let it cool slightly then pass the pulp through a passata machine or a sieve pressing it with the back of a spoon until all that is left in the sieve are skin and seeds. Return the sieved tomatoes to the pan (after first rinsing the pan) and cook over a low heat until it is reduced. It should reduce to a thick dark red paste. You will know when it is thick enough when you can draw a spoon through it and the sauce does not run back into the channel left by the spoon. When the paste is the right consistency spoon it into sterilised jars, add a layer of olive oil to cover the paste and seal immediately. Store in a cool dark place and refrigerate once opened.

For information on growing conserving tomatoes go to 

Tomato & Chilli Salsa (Mexican)

23 Aug

This is the salsa I make with our summer bounty of peppers, chillis, onion and tomatoes. It is a cooked salsa, bottled and heat processed, so it has a long shelf-life right through the winter.

A rich red tomato, chilli and onion relish perfect with home made corn chips or as a base for many Mexican dishes. I wanted to make this salsa for preserving so my starting point was the encyclopedic book on preserving Putting Food By 4th edition from which I took the basic ingredients and method.

Makes about 4 x 300g jars

  • 1 kilo of tomatoes
  • 4 hot onions
  • 10-20 green & red fleshy hot chillis peppers (preferably Jalapeno)
  • 1 large sweet green pepper
  • 1 large sweet red pepper
  • 1 tbsp ground mulatto chilli pepper (optional)
  • 50ml cider vinegar
  • 2 tbsp sugar
  • 1-2 tsp salt

Peel the onions and core and seed the chillis and peppers. Throw them into a food processor and grind to a fine chop. Peel the tomatoes and throw those in give the mix another quick wizz to pulp the tomatoes. Tip the whole lot into a large pan, add the rest of the ingredients and simmer for 20-40 minutes or until the salsa turners a dark red and has a rich thick consistency. Pour into sterilized jars and seal. Heat process for 15 minutes. See How to Make Passata for instructions on how to heat process in a hot water bath.

Cook’s Note Be careful with the chillis, if they are very hot use only a small number but if they are mild use 20 or more. Also the quantity of vinegar, sugar and salt required will vary depending on the variety of tomatoes used. If I’ve used beefsteak tomatoes like cuostralle, which are low in acidity I add the vinegar you may not need to just taste the sauce and adjust to taste.