[mihaifm]

One likely cause that's not mentioned so far, is that paradoxically the stomach doesn't produce enough acid. The sphincter usually closes when the stomach begins digestion, but this only happens if a certain pH threshold is reached. There are some receptors in the stomach that detect this pH level and signal the sphincter to close. The lower acidity output is typically caused by unhealthy diet and frequent meals. To fix it, apart from reducing the frequency of meals, you can ingest more acid, in the form of vinegar or lemon juice. This is counterintuitive but I can confirm it works, it helped me a lot to mitigate the problem.

[ricardobeat]

So the one-spoon-of-apple-cider-vinegar-everyday people might be onto something?