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The science of making porridge

The science of making porridge
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Perfect porridge can be a challenge. Too lumpy, too runny, too stodgy – unpalatable porridge is a sadly common phenomenon. Here, we look at how science can provide pointers on getting porridge-making right.

Let’s start with the porridge basics. Oats are around 40–60% starch. Starch is a carbohydrate which forms granules made of amylose and amylopectin. These are long molecules made up of glucose units – in amylopectin’s case, up to 200,000 of them. Amylose chains are linear, and tightly packed, whereas amylopectin is highly branched. This branching makes it more soluble than amylose.

Where things get interesting is when we start heating starch granules in water, as we do when we cook porridge. The starch granules absorb water, disrupting the hydrogen bonds between their chemical components. This causes the granules to swell. Over time, this swelling of starch granules causes the porridge to thicken. This process is starch gelatinisation; for oat starch, it kicks off when the temperature reaches around 60˚C.

As gelatinisation proceeds, porridge gets thicker and thicker. This thickening is known as ‘pasting’. It doesn’t continue indefinitely; around 95˚C, porridge thickness reaches its peak. After this, the continued increase of the temperature causes amylose to start leaking out of the starch granules. This slow breakdown and disintegration of starch lowers the thickness of the porridge.

Poor porridge making can be a consequence of a misunderstanding of the processes of pasting and gelatinisation. If your porridge mixture doesn’t reach the temperature required for gelatinisation, you get a grainy mixture of oats swimming in a liquid broth. If the porridge mixture is heated too high for too long, a similarly watery porridge soup results.

Even if you get gelatinisation right, it’s also important to factor in the fact that porridge continues to thicken for a time after heating. This happens as the starch granules continue to absorb water. Fail to take this into account, and you end up with porridge cake.

Of course, mastering these processes still doesn’t necessarily lead to perfect porridge. The ratio of oats and liquid that you start with will also affect the eventual consistency. Too little water limits gelatinisation. Most recipes recommend a 2:1 ratio of liquid to oats to avoid this.

Though porridge can be tricky to get right, some of its chemical components have benefits that make it worthwhile. Chief amongst these is a component of soluble fibre, beta-glucan. At dietary levels of 3 grams per day, beta-glucan can decrease cholesterol levels. This decrease may reduce the risk of heart disease. According to the British Heart Foundation, a 40 gram serving of porridge oats contains 2 grams of beta-glucan, so getting 3 grams a day isn’t unrealistic.

If that wasn’t enough reason to eat porridge, it can also keep you feeling fuller for longer after breakfast. This is another effect of beta-glucan. It helps form a thicker solution as the food we’ve eaten passes through our digestive system, making us feel fuller for longer.


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References & Further Reading