Patients who have suffered strokes will be assessed
Although most cases are spotted by doctors, there are still some which are hard to detect - and they could be dangerous.
In the normal body, a complex sequence of muscle actions both close the windpipe during swallowing, and propel food and drink down towards the stomach.
This stops food slipping down the windpipe into the lungs.
Food passing into the lungs increases the risk of chest infection and hospital stay - as well as reducing the amount of nourishment which actually reaches the patient.
In the UK, more than 100,000 suffer a first stroke every year - at any one time, 300,000 others are struggling to overcome the after-effects of a stroke.
Approximately half of them, immediately after their stroke, are thought to have some problems swallowing.
However, even those with apparently normal swallowing may be inhaling food - a process known as "silent aspiration".
Chest x-rays
Now a team of doctors is trying for the first time to work out the scale of the food-inhaling problem among stroke patients.
They are led by Dr David Smithard from the William Harvey Hospital in Ashford, Kent. The project is set to last three years.
In conjunction wtih Guy's, King's and St Thomas' School of Medicine in London, doctors will assess patients at the bedside - and also use chest x-rays to spot those who are mis-swallowing their food.
Patients can be given a liquid which includes a dye which shows up clearly in x-rays, so doctors can chart its progress down the throat.
Speech and Language Therapist Sharon Lewcock told BBC News Online: "This research is very welcome. There is definitely a small grey area in which it is difficult to spot patients with this problem.
"About 50% of patients will have swallowing problems after their stroke, and many of them can be identified quite easily because the signs are obvious.
"Speech and language therapists can often assess these people by the bedside and look for simple things - such as whether the Adam's apple is bobbing up and down."
She said that a national shortage of such therapists meant that proper assessment of stroke patients was "patchy" - although many doctors and nurses were now learning the necessary skills.
The latest research project is funded by medical charity Action Research.
Slow recovery
The disabilities caused by a stroke, which can involve paralysis or muscle weakness, are caused because a part of the brain are starved of oxygen because of a blockage or rupture in the blood vessel which supplies them.
Even short periods of oxygen starvation can cause long-term damage to neurons which control many vital muscles - including those which control swallowing.
Many patients recover some or all of their muscle function in the months and years following a stroke.
Strokes are one of the most common causes of death in the UK.