Urban Farming Oz

  • Increase font size
  • Default font size
  • Decrease font size

Preserving the Harvest

 Every farmer experiences bumper crops. In the urban environment this is true too. You plant enough tomato plants for the household, and get enough tomatoes for the street.

Preserving the harvest is the answer, and what that produce is, will determine how you can safely go about saving this food, or preserving it for later use.


The most common general methods of food preservation are freezing, drying and bottling, but there are more such as smoking, fermenting and salting.

My preferred method for fruits and vegetables is bottling. For me there isn’t much that can compare with the feeling of security and contentment that I get from having a pantry full of jars of home made jams, jellies, pickles, pasta sauces, soups and bottled vegetables

Modern Preserving Methods
During the mid eighties there was a quiet revolution happening in the “preserving world”. Old fashioned preserving methods were examined and found to be inadequate in many cases, and sometimes just plain dangerous.

Science came to the rescue, with a new set of standards. Here in Australia the CSIRO have referred us to the “USDA Guide to Home Preserving”, which primarily uses two methods for “canning” or bottling. These methods are the “Boiling Water Bath” and “Pressure Preserving” methods.

Choice of Method
When deciding on what bottling method to use to preserve your food you first need to determine if the produce is low acid or high acid. All of our food has a pH level, which is the measure of how acid or alkaline that food is. The pH level scale runs from 1 to 14 with 1 serving as “very acidic” 7 being “neutral” and 14 being “very alkaline”.

For example, most fruits are considered high acid foods, which means that they have a pH level of over 4.6.on the scale, covering from 4.6 to 1 on the pH scale. Tomatoes also fall into this group, but there are now such a variety of tomatoes, including tomatoes especially grown to be low acid, that extra care must be taken to ensure that the tomatoes used are not too low acid.

Most vegetables are low acid foods; which means that they fall below 4.6 on the pH scale, covering the range from 4.6 through to 14 on that scale. This covers such foods as green beans, corn, peas and many more. This would also include meats and seafood, which can be preserved using methods especially designed for low acid foods. You can change a food form a low acid food to a high acid food by adding acid. This is what you are doing when you are making pickles out of produce that under normal circumstances would be low acid, for example pickled beetroot.

High acid foods can safely be preserved using the boiling water bath method. Low acid foods cannot. Low acid food must be preserved using temperatures well above boiling and this can only be achieved at home in a pressure preserver, or pressure canner 

Pressure Preserving
One advantage of  preserving high acid foods is that the acidic environment will kill botulism. In the absence of this acidic environment higher temperatures are needed to kill both the living botulism and their spores.

Achieving higher temperatures than 'boiling point' or 100º C, requires an enclosed pressure vessel, as the boiling point of water increases with pressure. At sea level an additional pressure over and above atmospheric pressure, of 11lb or 5kg will result in a boiling temperature of 116º C. A home “Pressure Canner” can achieve this, and make bottling low acid foods safe.

Boiling Water Bath Method
The boiling water bath method of preserving high acid foods is necessary to prevent possible food poisoning and food wastage.

Simply put this method requires you to submerge the filled and sealed jars in hot water, and bring to the boil for a specified time for the food type and jar size.

Other, older methods, such as placing your hot food into a jar, closing the lid and hoping for the best is not acceptable. While preserving was done like this for years in the past, it inevitably resulted in cases of food poisoning, some that were not always able to be tracked back to their source.

The 'put the lid on and hope method', used by grandma, does create a partial vacuum, but there is still air trapped in the jar with your food. We now know that the air around us is full of bacteria, mould spores and other pathogens that can contaminate our food and cause illness.  Not using the latest technology in food safety is like travelling in a car without a seatbelt. You can still get where you are going, but not without greater risk.     

What you will need:
A big pot; something to put in the bottom of the pot to create a space to prevent the jars from sitting directly on the bottom of the pot; empty jars; new lids; tongs; knife; wide mouthed funnel; and a wooden spoon.

Prepare your jars
Wash the jars you are going to use in hot, soapy water and then rinse well. Leave them in a sink of hot water waiting to be filled with you pasta sauce. Do the same to the lids and leave them in a sink of hot water waiting to be placed on the jars once full. I use recycled jars from food purchased at the grocery store, but I use new lids to ensure I get a good seal.

If the processing time for a recipe is less than ten minutes it is recommended that the jars and lids should be sterilised in boiling water after washing.

Spread a towel out on your counter and when you are ready to fill your jars, place the jars on the towel, right by your pot. (This is where you need the tongs, so as not to burn your hands getting the jars out of the hot water.) You want the jars to be still hot when you are putting the hot food into them to. Hot liquid into cold glass can cause the glass to break, so be sure that your jars are left in the hot water right up until you are ready to start filling the jars.

Filling the Jars
Fill each of the jars using a wide mouth funnel, or your own creation, leaving a two and a half cm space at the top. Once the jars are full, wipe off the rims with a clean cloth. Be sure that there is no food on the rims of the jars, as anything that gets between the rim of the jar and the lid can stop you from getting a good seal.

Once you have cleaned off the rims of the jars you are ready to put on the lids. Using the tongs, get the lids out of the hot water and place them on the jars, tightening them all the way, but without over tightening them.

Processing the Filled & Sealed Jars
Now you are ready to process the jars to get the vacuum seal to ensure food safety.

Get the large pot and place the article you have chosen into the bottom to create a space between the bottom of the pot and the jars. This can be a round, cake cooling rack or something similar. Then place the jars into the pot ensuring they are not touching each other. Then using a jug, begin to fill the pot with warm to hot water. Do not use boiling water, but do not put cold water in as the glass jars are hot and once again you do not want to risk any jars breaking due to rapid temperature change. Fill the pot till the jars are completely submerged and the water covers the jars by 2.5 to 5cm.

Turn the stove on medium heat and bring the pot of water with your jars in it to the boil. Process the jars with the water briskly boiling for the time specified in the directions. If you have older directions without a processing time you can use that recipe, but you will need to find modern directions for preserves with the same ingredients and check the processing time. The  "USDA Complete Guide to Home Preserving" is ideal for this and can be accessed from http://www.greenlivingaustralia.com.au/USDAguide&more.html … the alphabetical section here is particularly good, except capsicums are bell peppers etc., and American pints are slightly smaller than Imperial pints … ( we have a conversion page here … http://www.greenlivingaustralia.com.au/conversions.html )

Once the time for processing has been reached, turn the stove off and leave the jars in the water to cool down. You want them to cool down slowly. There is no reason for you to risk trying to get the jars out of hot water and burning yourself, unless you have a jar lifter with which you can do so safely. Once the water has cooled sufficiently for you to safely remove the jars you can do so. Place the jars in a safe place to continue cooling as necessary.

As the jars cool down, a vacuum is created by the steam that expelled the air from the jars during the processing time, condensing. If you used ‘pop top’ lids, you will hear the ‘pop’ sound of the pop tops as they are drawn down by the vacuum created by the cooling jars. If the pop tops do not pop down that is an indication that you do not have a vacuum seal.

If any of the jars do not seal, you can process them again or simply decide that this is the jar you are going to use right away. There are several reasons why a jar may not seal. There may have been some food left on the rim of the jar, or there may be a defect, such as a chip in the rim of the jar. Also if you do not leave enough empty space at the top of the jar, you could prevent a vacuum being created.

Now your jars are cool and the vacuum seal has been created, you need to label your jars with their contents and the date. This is important as no matter how good your seal is, you do not want to leave a jar at the back of the pantry for years with no date on it. Always eat the oldest jar first. Even preserved foods that you purchase in the grocery store are dated with the use by date.

Once you get started with bottling you will soon discover that it is very rewarding, both in the personal satisfaction you obtain form taking another step towards self-sufficiency, and also through the financial benefits realised by bottling food from your own garden.

Here is our favourite Pasta Sauce recipe
So you have spent the morning out in the garden, and now you have a basket full of tomatoes and you have decided to make pasta sauce. Here is a recipe to get you started. 


5 kg tomatoes

5 medium onions

4 medium capsicum

1 Tbs Salt

1 Tbs oregano

1 Tbs Basil

4 Tbs sugar

Chop tomatoes, onions and capsicum and place in a large pot and bring to the boil. Reduce heat to medium–low and simmer, stirring occasionally to ensure that the sauce doesn’t stick to the bottom of the pot. Add the salt, basil and oregano. If you are using fresh herbs, increase the amount to two tablespoons of each. Add the sugar one tablespoon at time tasting as you go. The amount of sugar needed will be determined by personal taste and also by the type of tomatoes used. For example, Roma tomatoes are wonderful, sweet, sauce tomatoes and need little sugar added, if any at all. I have found that four tablespoons of sugar seems to be a good average, but I have used more or less on occasion.

The sauce will at first be quite liquid, but over time it will thicken up as the excess liquid boils off. How long you do this step will be determined by your personal taste of how thick you like your sauce and by the tomatoes you used. It takes me about 2 to 3 hours, depending on the tomatoes used, with the Roma tomatoes taking the least time.

Once the pasta sauce is done it is time for the next step which is the preserving step.

Boiling Water Bath process the filled & sealed jars.

For 375ml jars you need to process for 25 minutes, 500ml jars 35 minutes, and 1000ml you need to process for 40 minutes.

WARNING: Tomato is a high acid food that can be preserved using this boiling water bath method, but some tomatoes have less acid that others, Therefore, place a teaspoon of lemon juice, fresh or bottled, in the top of each jar prior to putting on the lid.

David Pearson




Sponsored Links