This is the burning and sometimes painful sensation which people feel rising from the pit of the stomach up into the chest. This occurs as the acid rises up into the oesophagus.
The lining of the stomach always produces a small amount of acid but this increases dramatically as soon as we start eating food. When the stomach is full, it not only has food in it, but it turns into an acidic bag, which churns and breaks down the food into small pieces which the body can absorb. This environment helps to start the process of digestion.
If people eat reasonable amounts, the food is let out into the small bowel for further digestion a little at a time. If people eat too much, however, the full stomach is under pressure. It needs to relieve that pressure, particularly if the owner of the stomach has a big belly, or is wearing tight clothes. The stomach has an escape valve, like an overflow valve in a hot water system. This valve or sphincter sits at the top of the stomach and allows gas and liquid to escape upwards into the oesophagus.
It often surprises people that these transient lower oesophageal sphincter relaxations (TLOSRs) occur particularly after eating. It is, however true, that most episodes of acid reflux happen within two hours of eating. They are more common after eating particular foods and the larger the meal, the more likely TSLORs will occur and that the person will suffer acid reflux symptoms.
A number of factors will influence how likely you are to suffer TLOSRs. If you have a hiatus hernia, the lower oesophageal sphincter will work less well. Coffee relaxes the sphincter rather too much and is the cause of a lot of misery. New drugs aim to decrease the frequency of TLOSRs.