As an experiment, I made five jars of grape jam/jelly. I then processed three of the jars in the boiling water bath and left two of the jars, with lids secured, on the kitchen counter to see what happened. Here is the result.
As you can see, the two jars that I did not process in the boiling water bath were both contaminated with mould. This is because even with putting hot jam into hot, sterilized jars, you still have some air trapper in the jar with your jam. The air around us in contaminated with bacteria, natural yeasts and moulds. Once these contaminates are trapped in a jar with the remaining air, the moisture and food they have access to can explode their population significantly. Just one bacterium can multiply to over 2,000,000 in as little as 7 hours.
What you need to do is use the boiling water bath method to create a full vacuum, by expelling all the air out of the jar. When you put hot jam into a hot jar, as the jar cools, the contents contract and it appears to create a vacuum; however, this is only a partial vacuum and is not enough to prevent the above contamination.
Micro-toxins and Your Health
There is an excellent web site for further information here:
I have quotes just a few key points below.
“Micro-toxins are poisonous substances produced by certain moulds found primarily in grain and nut crops, but are also known to be on celery, grape juice, apples, and other produce. There are many of them and scientists are continually discovering new ones. The Food and Agriculture Organization (FAO) of the United Nations estimates that 25% of the world's food crops are affected by micro-toxins, of which the most notorious are aflatoxins.
Some moulds cause allergic reactions and respiratory problems. And a few moulds, in the right conditions, produce "micro-toxins," poisonous substances that can make people sick. When you see mould on food, is it safe to cut off the mouldy part and use the rest? To find the answer to that question, delve beneath the surface of food to where moulds take root.”
Moulds can thrive in high-acid foods like jams, jellies, pickles, fruit, and tomatoes. But these microscopic fungi are easily destroyed by heat processing high-acid foods at a temperature of 212 °F in a boiling water canner for the recommended length of time.
Looking back at the photographs of my mouldy jam, you can see a definite green tinge to the mould. Here is some back and green mould under a microscope.
You can see the long roots that would penetrate into he food on the green mould, so if your jam, or any other food for that matter, gets mouldy, throw it away.
So boiling water bath please and enjoy wonderful food and good health.