A guide to making jam

The Rhubarb season has started and what time could be better to bring up the topic of preserving fruit and vegetables in jams. Making jams is a beginner friendly method to preserve your favorite seasonal fruits to enjoy them all year round. However, there are some points that you need to pay attention to when making jam and this guide will help you to avoid common mistakes. 

The ingredients 
The most important ingredient is probably the fruit you add. The classics are of course strawberries or raspberries but you can also use vegetables like the previously mentioned rhubarb. The adventurous might even want to add tomatoes or cooked pumpkin. You can also experiment with adding herbs such as mint or rosemary or spices like vanilla, ginger, chili or pumpkin spice. However, for a beginner I would recommend trying some of the simpler and classic versions before you start experimenting. If you want to try something new but you are unsure if it will taste good, you can cook a batch of jam and fill it into jars but leave the amount for one jar in the pot. Now you can add herbs and spices and fill it in the remaining jar. In this way you do not end up with several jars of jam that you might not like. 

The second vital ingredient is jam sugar. This is a sugar that has a gelling agent added. Usually, the vegan-friendly pectin is used, however, you might want to make sure there is no gelatin added. You can find jam sugars in the store and the package will give you instructions for how much fruit it is suitable for. This is given in a ratio of fruit to jam sugar. For example 2:1 means two part fruit to 1 part sugar; so this could be 1000g fruit to 500g sugar. Most common ratios are 1:1, 2:1, and 3:1. The higher the sugar content the cheaper the jam while more fruit makes it tastier and slightly healthier. Sometimes you can also find small packages of the gelling agent that you can mix with sugar yourself. This gives you also the opportunity to use sugar replacements. You can read what impact this has on your jam in the food safety section.

The Jar
Of course you can go to a store and buy some fancy empty jars. But this might get quite expensive. Alternatively, you can reuse the jars that you buy in a grocery store. For example chickpeas, tomato sauce and many more items come packaged in jars. You can simply wash them and store them until you have enough. Make sure the jar has a lid that seals tightly; this is usually the case for metal lids but not for plastic lids. Also do not use lids that smell like the food that was previously in the jar; this is often the case for pickles. Otherwise your jam might take on a pickle flavor which is usually not pleasant.     

Always stir during boiling
It is important to continuously stir the jam during boiling otherwise you risk the jam to get burned at the bottom of your pot or not firm up evenly. 

Find the right consistency
Two main things that have an influence on the consistency, how big or small you cut your fruit and the amount of jam sugar (gelling agent) you add. You can cut the fruit in rather big pieces to create a jam with chunks of fruit or you can puree the fruit to give a smooth jam. You can also let the fruit rest with the ja sugar added to drain some of the moisture from the fruit.

The amount of jam sugar you add determines how firm the jam will be. Usually, you are pretty safe to follow the package instructions. If you have a very liquid starting mixture, for example fruit juice, you can add more jam sugar right at the beginning. The gelling agent in the jam sugar needs heat to be activated and firms up only after cooling down. So the problem is that right after boiling you can not say if you have used enough jam sugar but if you have filled up all your jars and then realize the jam is not firm enough it might be too late. This is why you should test your mixture after boiling. To do so you put a teaspoon of your boiling jam on a small plate. Thin out the jam to a thin blob and wait for it to cool down. If the jam on the plate firms up when cool then you can start filling up your jars. If not, you can add more jam sugar. Also note that the right consistency is the consistency that you like most. 

Food safety
There are three vital steps to make sure that the jam is safe to consume even after months (and sometimes even years). The first is that you need to add enough sugar. In supermarkets you can find jam sugar with a ratio of 3:1 (so you can add three times more fruit than sugar, e.g. 1500g fruit to 500g jam sugar) and this is the lowest sugar amount you can find. So going below that might mean that your jam does not last as long. However, you can also buy the gelling agent without added sugar. You can add the sugar yourself but you can also add sugar replacements. But you might want to store even your unopened jam in the fridge. 

A second important point is to use clean jars and sterilize them with boiling before filling them up with jam. This makes sure there are no germs on the jar. 

And the final point is to fill the jam in jars while it is still hot. This has the advantage that remaining germs in the jar get killed but also that when the jar is sealed and cooled down it creates a vacuum in the jar. In older instructions you might read that the jars need to cool upside down to create the vacuum, however, this is not the case. If the jar is sealed properly and the lid fits tightly the vacuum is created by the air in the jar, which shrinks when it cools down. Therefore, it is a good way to check if your jam jar is sealed tight so no germs can come in. If you realize that some of your freshly filled jam jars don’t have a vacuum this is not a problem. You can store them in the fridge and use them up first. However, if there is no vacuum on a stored jam jar this is a warning sign that the preservation did not work properly. Be extra careful when testing if the jam is still okay to eat. When the jam smells or tastes bad or you see a moldy layer on top of the jam it is better to throw it away than risk food poisoning. You might find it hard to open the jam jar because of the vacuum. In this case you can use the handle of a spoon, stick it between lid and jar to remove the vacuum when you want to open a new jar of jam. 

Now that you have equipped yourself with the knowledge of preserving fruit and vegetables in making jam, you might give it a try with our Banana-Rhubarb-Jam recipe.

Written by Laura Lang
Photo 1 by bluemasonjars; (CC) , Photo 2 by Waleed (@65WZ); (CC)

Published by bruisedfoodclubuppsala

Non-profit organisation that saves food, reduces food waste and hunger and promotes sustainable food consumption.

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