Toddler holding food in mouth - how to handle?

[Gargula]

I've just had mealtime from hell with my 2.7 yr old.
Up until recently he has been a good eater - recently he has become a lot more fussy, which I'm putting down to his age and also the arrival of his baby sister.
I don't particularly mind if he decides not to eat his food - he doesn't get an alternative and generally has a healthy diet.
But he has now developed a habit of holding one or two mouthfuls of food in his cheek for ages and just not swallowing it.
He did this just now at lunch and I think I handled it very badly. I insisted he swallowed it before being allowed to leave the table but it was almost like he had a mental block about it. I was probably more angry than I should have been and he did get upset and a bit sick (he has reflux so not altogether uncommon!). Ultimately he didn't eat this mouthful of food and spat it out when I said he could.
The whole experience was upsetting for everyone and he is now sleeping it off upstairs.
How do I deal with this holding food in his mouth? Do I ignore it or do I insist he eats it, or let him spit it out.
I had a lousy relationship with food (basically only ate one or two things till 18!)and don't want to create the same issues for him.
Any ideas?

DS went through a phase of doing this, drove me nuts! I tried not to make a big deal of it but made sure that he only ate when sitting up at the table. Then if he held food in his mouth, I'd tell him he could either swallow it, or spit it out before he could get down. I'd try and ignore him as much as possible (clear the table, for example) but if he asked to get down I'd say "course you can, just swallow that food or spit it out if you don't want it, then we can play".

DS is always allowed to spit food out if he doesn't like it, as long as he does it nicely! I want him to try new things but have a "get out" option if he doesn't like it so spitting is acceptable, in our house.

I think it's just a control thing. If you try and show that it doesn't bother you, it'll probably pass soon enough.