It pretty much relates to "osmolality"... The chemical concentration of a liquid will shift fluid through a semipermiable membrane to "balance" the chemical concentration on either side of that membrane... As the complex chemical sugar begins to disolve in the mouth & throat, the (high) concentration of the organic chemicals begins to pull fluid from the (mucus) tissue in order to "balance" the concentration of that fluid (osmolality) on either side of the tissue wall ( "pulls" the mucus ('fluid'] from the tissue) ... That, plus the drying effect of the sugar is probably is what causes the coughing. That's my story & I'm sticking to it...!!
Either eating pineapple or drinking pineapple juice (any acidic juice) will cut the mucus.
The following is in plainer English. Sorry, Gordon.
A website I found helpful was www.health-science-spirit.com/diseasesummary2.html. Here they explain that the sugar is good because it works to draw out the mucus. So, I guess it doesn't cause mucus!
The lactose in milk is the reason we get sick from too much dairy product. Lactose, like all other sugar types ups the production of mucus, sending it to your throat, nasal cavaties and ears. I always thought that this was common knowledge, but I guess not.
Mucus is caused by the body, as it uses alkaline materials to get rid of any acidic waste that it needs to, at that stage in time... if we don't want the mucus, we need to avoid making our bodies react in this way.
If you would like to understand your body and why it reacts the way it does, google acid alkaline and/or pH Miracle...
Gordon you are fantastic. Finally someone gets it. It's so simple to. I suffered for years due to this. Low carbohydrate eating has set me free.