It’s summer and these days we have been doing something we love: pick blackberries. Have you ever imagined what a scientific experience it can be to hand pick blackberries and transform them into a delicious jam? You know I am convinced that almost any activity you can perform outside in nature, can provide a scientific knowledge. Just to start: we found the best places to find berries, we compared the maturity point of different berries (color, smell, taste…). We compared the taste of berries from different plants trying to identify the characteristics of the most tasty ones. We have found the deterrent power of their prickles…a scientific research project.
But learning continued at home when we made jam from the hand picked berries. We followed this recipe with a delicious result:
But would you like to know a bit more?
In the past, it was a very extended custom to preserve the excess of seasonal fruits in the form of marmalade, jam or compote. Why? Sugar, like we have previously seen with salt, acts as a preservative, mainly because it extracts (by osmosis) water from the food with which it is in contact, while penetrating inside. This water extraction results in a reduction of microbial activity. If you would like see an extended explanation you can check this article published in “Scientific American” jounal.
Why do you need to boil the jars?
In order to sterilize them, i.e. kill any microorganism that could be present in them, which do not survive to high temperatures. In the first sterilization you kill the microorganisms in the jars and lids. In the second, you do the same with the jar content: the jam and the small air bubble on top; and the outside of the jar, that could have smeared during the process.
How is vaccum made in the jars?
When you put the jam in the jars, both the content and the jar are hot. When you put the lid on, a small hot air bubble remains on the top. When this air gets cold, it shrinks, creating a pseudo-vaccuum inside that pulls at the lid, sealing the jar. The typicall “plop” that you will hear when opening the jar is produced by the air going back into the jar. If the jar is correctly sealed, the absence of air inside the jar, makes it impossible for aerobic bacteria to grow inside.
Another interesting learning point: we have also learned about food processing, self-supply, and use of natural resources. In summary, a very productive session, don’t you think?