HOW FOOD WORKS: An Introduction to Jam Making
How jam becomes jam, the role of sugar, what exactly is pectin
Hey Friends!
I know some people find jam a bit intimidating, so I hope this deep-dive settles your nerves, and equips you with some confidence to go off and make your own concoctions!
If you do end up using this recipe, or making your own from what you’ve learnt, please let me know! And also, if you’re enjoying this newsletter and think you may know people you would enjoy it too, please pass it on! There’s nothing better than word-of-mouth in my opinion.
Happy Wednesday, and as always, thanks for reading!
Fiona :)
Cast your mind back to learning about the Ancient Egyptians in school, with their beautiful tomb paintings of hieroglyphics and pharaohs - do you remember any inscriptions of food? Well, jam is thought to have originated way back then, as a way of preserving fruits past their season. As time went on, the idea spread to Europe, then the Middle East, and the recipe took on a new look, replacing the traditional honey with sugar, thanks to the newfound craze of sugarcane.
Back then, you obviously didn’t have the option to whack things in the fridge. The act of preserving gave a solution (for those who could afford the ingredients), to enjoy the earth’s gifts over long stretches of time, with little risk of ingesting something bad.
Jam hasn’t really changed much since the 7th century to be honest. The formula is really pretty simple, it’s just a technique (like so many) that seems to put people off. I guess it’s hard to justify making it when you can get a pre-made version nearly anywhere, for next to nothing. But, I have to be honest, what you get in the shops is nothing compared to what you can create in your kitchen. The flavour, the texture, the smells - it is honestly a delicious therapeutic experience, and one that’s definitely worth your time!
The Breakdown:
Jams are pretty much fruits cooked in sugar. If the fruit is citrus, the name changes to marmalade. If there is no fruit completely, and it’s replaced by milk, the name you’d be looking for is ‘milk jam’ (bit of a stretch, I know).
Today, we will be focusing on jam making, and I will be attempting to distill everything I’ve learnt into a neat bank of rules so you can effectively make any jam you want. Don’t like rhubarb? Don’t sweat it. This is the playbook, you are the coach. What you do after reading is your call. This week’s newsletter will just make sure it’s a good one.
- The Transformation
At a high level, jam doesn’t contain sugar just for sweetness. Fruit is mostly water (85-93%), and water, is a bit of a flight risk. Why? Its presence allows the multiplying of microbes, A.K.A. bacteria, fungi, viruses and protozoa. Microbes are everywhere, they don’t just spawn out of thin air, and so we consume them all the time. If, however, we ingest too many, or too many of the bad kind, it could make us really ill.
Sugar LOVES water. So much so, that once she’s in contact with it, she tightly binds to it, luring it away from the fruit it was once cosying up with. The fruit, abandoned, can no longer host microbe growth on its own. Microbes just aren’t that interested unless water’s around.
This is great for us jam makers, it means we don’t have to worry about spoilage. We just need to make sure things stay that way. But, how do we do that?
- The Sugar
Natural sugars are already present in fruit. We then add more sugar to make jam. The amount of sugar you add needs to be within a window. Classic ratios are 50:50 sugar to fruit, with adjustments common for +/- 5%. To decide your sugar amount, you need to consider three things: how sweet do you want it, how sweet is the fruit already, how much pectin does the fruit have?
Although personal preference of sweetness is a factor, if you wander too far, bad things can happen. If you use too little sugar, fermentation can occur as there isn’t enough sugar to bind to water molecules. The fruit and water are back together again, happily hosting all of the microbes, and your jam is sort of ruined. Too much sugar can result in the jam not setting properly. It can strip away too much water from the fruit cells, dehydrating pectin (we’ll talk about this more later), and thus leaving us with a runny mess. Too much sugar can also crystallise the jam or, by raising the boiling point, destroy pectin’s structure, preventing gel formation.
If the fruit is really sweet, you can consider dropping your sugar content to 45-50%, (notice how we never really go outside of the 45-55 perimeter). Fruit can be naturally really sweet (e.g. grapes, cherries, pineapples), or it can be very ripe and therefore very sweet. Using really ripe fruit isn’t really recommended as the microbial presence is probably already quite high, making it hard for us to ensure a lasting final product.
The pectin level in fruit also helps determine how much sugar you should use. Low pectin requires more sugar to help extract more water. High pectin needs less sugar to reduce too much gel formation resulting in a rubbery, stiff jam. In order to better understand why this happens, we need to understand pectin and its role first.
- The Pectin
Pectin is a long chain insoluble carbohydrate, containing negatively charged carboxyl (-COO⁻) groups. It bonds to water in the cell walls, giving fruit its texture. When making jam, we don’t want it to do that anymore. We want pectin to leave the cell walls and bond to each other. This creates a whole new texture, the gel-like quality of jam. We facilitate this happening in three ways.
When we cut fruit up and macerate it (soften by mixing it with sugar), water starts to leave the fruit to form a syrup with the sugar. If we examine more closely, we see that water mainly leaves from inside the cells, and some leaves from the pectin-water bonds. This results in the fruit becoming softened, but still keeping its structure intact. Pectin molecules are now more accessible, but they are still tightly bound to the cell wall and insoluble.
When we add heat, the cell walls start to break down, releasing the pectin molecules into the liquid mixture. As the temperature increases, pectin molecules start to dissolve into the mixture, becoming soluble and free to move and interact with each other. The evaporation of water and addition of sugar keeps the water molecules away from pectin, forcing pectin strands into closer proximity although they’re still opposing charges.
When we add acid (H+ ions), the negatively charged carboxyl groups (-COO⁻) in pectin are neutralised, stopping the pectin molecules from repelling each other. They can now move even closer to one another, and as the jam cools, they form a gel that results in the texture of jam as we know it. If there isn’t a lot of pectin present, we can increase the acid content to promote pectin bonding, and vice versa to avoid an overly rubbery and solid jam.
- The Temperature
104°C comes up a lot in jam making literature, and for good reason - it’s crowned the perfect point for jam setting. Pectin, sugar and acid all behave their best, and so you get recipes that tell you to just stick a thermometer in and wait until you hit this sweet spot - that’s how you know your jam is done.
I have a bit of an issue with this. The first is you need a thermometer, not something that’s common in your average kitchen. The second is I am always sceptical of ancient recipes that call for modern equipment. In some cases I appreciate it drastically reduces your stress levels, but in this case I sort of feel like it does the opposite.
Staring at your thermometer, holding it in place, all whilst mixing a jam spitting at you, is quite intimidating. It may even be the source of some of jam makings bad rep. But to add salt to the wound, this method doesn’t always work. Relying on it alone can still result in a jam you’re not happy with, and I think it’s really down to the many changeable factors. Other, non-thermometer based, easier tests, are still needed to get things right, so you may as well just use those.
Your jam does need to boil, if it doesn’t you’re at risk of not providing enough heat for the pectin to break down. Once it hits higher temperatures (still below 104°C), it noticeably thickens, and you can reduce the temperature right down to avoid going too far above the sweet spot. All of these steps you can clearly judge by eye, you can absolutely use a thermometer if you like, but you also absolutely don’t need to.
- The Preservation
To make sure all your hard work doesn’t go to waste, you need to make sure whatever you’re storing your jam in, is also free of microbes. You want to do this by making sure your jars are thoroughly cleaned and disinfected by either baking upside down at a low temperature of around 120°C for 20 minutes in the oven, or boiling them and drying upside down. You want the jars balanced on a perforated baking rack (your oven usually has one of these, just make sure it’s clean!). The upside down technique prevents the collection of airborne contaminants settling inside the jars.
To read the recipe with step by step explanations, subscribe to receive ‘TEST KITCHEN’ where we will also go over the comprehensive cheat sheet for this technique, troubleshooting, key details, graphics and science backed flavour pairings.
Happy eating and thanks for reading!
Fiona :)
Any questions, let me know below!