A critical principle underlying texture modification of foods and liquids is their thickness. For someone with dysphagia – swallowing difficulties – it can mean the difference between swallowing safely or choking.
In this, temperature is a key consideration: according to the law of physics, it changes the viscosity of liquids. Typically, liquids are thicker when cold and become progressively runnier when served at room temperature or heated up. Think of the difference between pumpkin soup served after being cooked on the stove or taken out of the fridge, when it becomes a lot thicker. Or imagine trying to pour candied honey – it’s much easier if it’s warmed up.
That’s why the International Dysphagia Diet Standardisation Initiative (IDDSI) factor temperature in with their flow test to inform guidelines for health professionals serving texture modified foods and drinks to patients.
How thick should it be?
Texture modified foods and liquids have different rankings according to their texture and viscosity, respectively. These are related to the complex physiological processes involved in swallowing and a person’s source of difficulty performing this act that seems so deceptively simple to most of us.
For instance, according to a systematic review by Catriona Steele and co-authors, a thicker liquid allows more time to close the airways and avoid it going down the wrong way. But it can also carry greater risk of pooling in the throat after swallowing. So in these cases it might depend on whether the problem lies with airway closure or weakened muscles required to push food down, requiring careful clinical assessment of swallowing capability.
The flow test
Measuring the thickness of a liquid is done by timing how long a specified amount takes to flow through a narrow pipe called a viscometer tube. This method can be used to judge how the liquid’s thickness changes as it cools down.
Liquids are typically modified by adding thickeners to create consistencies previously compared to nectar, honey or pudding. Due to widespread variability in the understanding and nature of these foods, IDDSI now describes them on a scale ranging from slightly thick (level 1) to extremely thick (level 4).
Manufacturers need to factor in the variable effects of time and temperature on this process, and IDDSI recommends that it is done under the intended serving conditions. Once a desirable thickness is established, they need to specify the correct serving temperature on the label and this should be observed during audits.
If food is texture modified before being cooked, it’s important to cook it as soon as possible, and certainly no longer than one hour. People administering the liquid should also ensure it doesn’t sit around before being consumed.