Cranberry science & Why cranberries make a great jam

Every year, around the American Thanksgiving holiday, the internet seems to be full of cranberries again. We’ve looked at these native to North America fruits before, when using a flavour pairing tool to determine that they work great with brie and walnuts.

But there’s more to cranberries for the curious mind, why do they make jams so easily? And what would be their European equivalent?

Introducing American cranberries

Cranberries are some funny little fruits.Not only are they quite tart, they’re probably one the few fruits that, as long as they’re still good, can bounce a little when you drop them on a solid surface. This is because cranberries contain large pockets of air (making them light) with a sturdy outside.

Cranberries originate from the North America continent where they’re harvested in fall, which probably explains their popularity during Thanksgiving and other festivities in that time of year.

fresh and sliced cranberries
Fresh cranberries, some are sliced through the middle to show the air pockets (and tiny little seeds which you won’t even notice when you make it into a jam).

What about lingonberries?

If you’re ever been to IKEA, you’ve must have seen their lingonberry juice, or lingonberry sauce, served with their famous meatballs. Even though they are closely related to the cranberry, they’re different. They are smaller and have a slightly different flavour profile.

Cranberry composition

When scientifically analyzing a food, you’d always want to know something about their chemical and physical properties. Which molecules are present and what about that pH-value?

Cranberries are very acidic, comparable to lemon and limes (which have a pH-value of only 2,2-2,3. For comparison, apples & grapefruit have a pH-value of around 3 and most other fruits are less acidic than that. Since they also contain quite little sugar compared to other fruits, this makes them quite tart to eat.

Powers of cranberries

The low pH-value ensures that cranberries keep quite well. Micro organisms cannot grow well in those conditions. But there’s more. They also contain a lot of phenolic components. Some of them have antimicrobial properties, meaning they prevent growth of micro organisms. Others contribute to flavour and astringency.

The colour of cranberries

Cranberries have a nice dark pink/red colour. It gets this colour mostly from the anthocyanins. This is similar to the colour of rhubarb and also has similarities to that of red cabbage. If you’d like to learn more about red colours in foods, we’ve got a whole post on the topic of red.

cranberry jam in glas jar

Why cranberries make a good jam (and sauce)

Jam (here’s the more elaborate post on jam science) is a concentrated version of fruit + sugar. It doesn’t contain that much water anymore and has thickened up considerably. When making jam you’re essentially trying to make a gel, but without using something like gelatin which creates a different texture again.

Optimum conditions for pectin

In jam that gel is formed using pectin. Pectin is a large polysaccharide that is naturally present in a lot of ripe fruits, but in varying concentrations. Pectin sits in the cell walls and dissolves from the fruit while it is gently simmering away while being turned into a jam.

The optimal conditions for pectin to do its work in jam are a pH-value (= acidity) of 2,8-3,5, and a pectin concentration of 0,5-1,0%. Unfortunately, I wasn’t able to find the pectin concentration of cranberries, but the literature generally agrees that cranberries is acidic enough and contains enough pectin for the pectin to create a gelled jam. You don’t need to add any additional pectin and no extra acidity (by adding sugar and diluting the cranberries, you’re already increasing the acidity somewhat).


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cranberry jam in glas jar

Cranberry jam

  • Author: Scienchef
  • Prep Time: 5 min
  • Cook Time: 90 min
  • Total Time: 1 hour 35 minutes
  • Yield: 1 medium sized pot of jam

Description

A very simple cranberry jam, you can add extra spices or flavours (see the jam in the Victorian sandwich) but this one works just fine.


Ingredients

  • 250g cranberries
  • 200g sugar
  • 200 ml water (since you’ll be cooking the water off try adding less if you can, as long as all the sugar dissolves and it doesn’t stick to the pan at the start and you’re good)

Instructions

  1. Place all ingredients in a small saucepan and bring to the boil. Once its’ boiling you will see the cranberries breaking apart and softening. This is when the pectin comes free.
  2. Continue to simmer on a low heat (you don’t want it to burn at the bottom) until it is either 105C or until it’s reached the consistency you’re looking for.

Notes

This is quite an acidic jam so can be suitable for canning when you use the right equipment and tightly control sugar content and acidity.

This makes for a thick jam with cranberry skins, it isn’t super smooth. If you want a smoother jam, put your mixture in a food processor or blender just after the fruits have softened, but before it’s thickening up completely. You could do it later, but that just makes it harder to clean and get out again. After blending, continue cooking.

Where do you cranberries come from?

This video below shows you how the cranberries are processed after they’ve been harvested.You might not realize, but there’s quite a lot of high tech involved when packaging and sorting fruits (but also vegetables). Companies use lasers and other visual techniques to determine which fruits are suitable and which are not. In the case of cranberries, those cranberries that are too light in colour or have been damaged are sorted out. In the case of ice berg lettuce for instance it is used to sort our parts that have started to brown.

Further reading

Robert Baker of the USDA tested the pectin content of various fruits, unfortunately, he did not analyze cranberries.

This farming blog shows som nice photos of the harvest of cranberries.

The national canning center states that cranberries have a pH and pectin content that makes them suitable for making into a jam without adding anything else.

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