As the weathermen seem to be saying that winter is finally about to release its icy grip, I thought I might repost this in anticipation of a bumper summer harvest. Well we can live in hope can’t we – lol!
The Jam Making Lament: “The more I boil it the worse it gets!!”
You know, by far and away the largest number of questions I get asked are concerned with the setting of jam and jelly. It seems that many people wrongly view jam making as somehow akin to making toffee or caramel, as in, “… the more I boil it the harder it gets.” Unfortunately, in reality this could not be further from the truth and in fact the addition of too much heat will prevent a jam or jelly from setting at all. So what is the science behind jelly and jam making and what’s more if we understand it will it make us more able to produce good preserves in a predictable fashion. Well the answer to that question is; firstly, the science is actually quite interesting and secondly, once understood it will most certainly make us better jam makers.
So the obvious question to ask and logical place to start on our quest to understand the science of jam making is “What makes jam set?” The simple answer to this is pectin. Now we’ve all heard the word pectin banded about but how many of us actual know what it is, what it does, and how it does it. I suspect not many. In the simplest of terms pectin is the building blocks, the bricks and mortar if you like, of the gel that gives jam and jelly structure. It is the substance that in effect turns a liquid fruit syrup into a solid jam, in the same way as gelatine is the substance that turns your jelly for the sherry trifle from a hot runny liquid into a solid wobbly layer between your booze soaked sponge and the cold custard.
D-Galacturonic Acid the building blocks for jam making
Ok, but what exactly is this pectin stuff made of. Well the pectin molecule is made up of lots of smaller molecules all joined together in a chain. We call these chains polymers in the scientific world and the pectin polymer is made up of long chains of a molecule called D-galacturonic acid, which is a distant relative of the sugar we put in our tea. In nature this pectin polymer is found in the structural cell wall of plants and along with cellulose it gives the plants there rigid structure. Good sources of pectin are apples and citrus fruit peel and these, indeed, are used to produce pectin on a commercial scale for the mass production of sweets, jam making and of course to sell to us amateur preservaholics to splash around liberally when things haven’t gone quite to plan!
So I hear you cry “that’s all very well but how does it work!” Well attached to some of these Galacturonic acid molecules making up the pectin polymer chain are little chemical hooks called methyl esters, and under certain conditions, which we will come to later, they grab hold of each other, connecting the pectin polymer chains up in a random tangle, a bit like a tangled ball of string. It’s this tangled lattice work that is the gel, holding all the water and fruit in a kind of slightly solid, slightly liquid, wobbly mess we recognise as jam. The number of little hooks can vary depending on the source of the pectin, and more frequently today, how it’s been fiddled with by man in the laboratory. But suffice to say the more hooks the stronger the polymers bind together and the firmer the gel.
Now we come to the interesting part. How does this intimate knowledge of pectin help us with our jam making. And more to the point can it put to bed some of these ridiculous myths that surround the art of the jam making process. The answer is yes it can, however, we need to arm ourselves with four more vital pieces of information before the curtain of mystery can fall. Firstly, pectin is soluble in water and the more water available the further the pectin polymers will be apart and therefore the less likely they are to link up to make a gel. Secondly, sugar binds water up and makes it unavailable for the pectin to “float around” in; thirdly, the hooks on the pectin polymers will not grab hold of each other unless they are in an acidic environment. And finally, now for the real bombshell – once all these conditions are met, this hooking up process occurs as the jam cools!
So what are the implications of those four statements for our jam making process. Well firstly, we can dispel the “boil it to death” school of thought, as the gelling actually occurs as the jam cools down. All that is required is enough heat to make sure the pectin is dissolved – simply bringing to the boil is more than adequate for this. It also tells us that acid, either in the form of lemon juice or pure citric acid is essential for our jam making to be successful. And last but by no means least it tells us we must have enough sugar present to “starve” the pectin polymers of water so they start to hook together – the magic number being 55% weight/volume sugar to water/fruit pulp or juice.
In summary then, heat is only required to soften the fruit, extract its flavour and natural pectin and to make sure the pectin is fully dissolved. The myth that heat somehow drives the gelling process has hopefully been dispelled for good. Acid must be present in sufficient quantity to allow the pectin polymers to cross-link, and incidentally it also helps in extracting the natural pectin from the fruit. Lastly, enough sugar must be added to bind up sufficient water away from the pectin such that it starts the cross-linking process. And that as they say is that!
What we can take away from this though is a universal recipe for jam making, that by and large will work every time for every fruit. The only variable being how much pectin the original fruit contains and therefore how much extra water you can add to your recipe, assuming you want the highest yield of jam from your fruit, and it still to set. This is of course a matter of judgement that comes with experience and would be wisely based on the results of a pectin test of the boiled fruit, which is relatively easy to carry out. As a general rule, high pectin fruits, such as citrus can take anything up to 3 times their weight in water, where as the soft fruits at the other end of the pectin spectrum should be soften to a pulp in a damp saucepan and no more.
So if we set aside for one moment the variable of how much water to add to the fruit can we write a universal jam making formula. Well let’s have a go:
- Always choose fruit that is slightly under ripe as it contains more pectin.
- Cut into appropriate size pieces, place in a saucepan with a tight fitting lid and add a generous teaspoon full of citric acid to every kilogram of fruit.
- Bring the fruit to the boil with the lid on tight and simmer for 5 to 10 minutes or until the fruit is a pulp. Remember, the quantity of water added at this stage is dependent on the fruit you’re using. Consulting a recipe book for guidance purely on this aspect of the process is probably the easiest thing to do.
- Remove the lid, add sugar at 1.2kg to every 1kg of fruit pulp and bring rapidly to the boil.
- Check you have a rolling boil as shown in the picture below, hold for 30 seconds.
- Turn off the heat, allow to cool slightly, descum and decant into sterilised jars.
The rolling boil essential in jam making
And that really is it. I hope that has busted the myth of jam making for you. I can already hear the cries of “what about low sugar jams” and “you haven’t mentioned aminated pectins” and so on. I am fully aware that there is a whole load more to the art of jam making and hopefully we will be able to go into that in greater detail in other blog posts. For today I hope this has just helped to lift a little of the mystery that surrounds the standard “old-fashioned” jam making process, and will give some of you out there a better understanding of what you are doing and improve your enjoyment of jam making in the future.