Why do my pancakes fizz? TL;DR: Usual pancake (French-style crepe) mixture causes separation of mixture in the blender and fizzes when fried resulting in very poor quality pancakes which burn easily.

The last couple of weeks I made flat (not fluffy) pancakes with this recipe:


500ml semi-skimmed milk (green top for those in the UK)
approx 200ml gluten-free flour (it was tipped in without measuring, but that's how I always do it) - by volume this would be about 1/3 of the milk measure
2 fresh medium eggs (bought the day before, stored in fridge)
1/2 tbl spoon of vanilla essence, aka a 'splash'


The method?.. Stick it all in a blender, run for 10 seconds, scrape/scoop any unmixed flour from the sides, run for another 5 seconds, fry (no oil.)

Last week I got a really nice, thin, medium-golden set of pancakes. Literally every single one cooked beautifully in seconds, curled at the edges just so I could flip and were thin, tasty and perfect.

This week the mixture fizzed (yes, 'fizzed') as it hit the pan. The holes appearing as it fried were huge and at the edges it seemed to stick straight to the pan and just burn straight away. It did not curl and I had to get the spatula (thin, metal) forced under the edges to be able to peel them and flip. The underside burnt and until the mixture cook firm the liquid mixture continued to make the disturbing fizzing. Just before flipping I could see a sort of mottling on the top, completely unlike any pattern a regular pancake would have. After flipping the second side would not brown at all - just go from white to burnt. They tasted OK, but not like last weeks'.

This is how I always make pancakes, but every-so-often they come out with this irritating 'fizz' sort of sound and it's at that moment I know they are going to be a pain to fry.

The one other indicator I get is that when I finish blending the mixture together, the top is bubbly and clearly separate from the regular part of the mixture. I just can't figure out why it would separate like this - what is the cause of the low quality mixture? The ingredients are always bought within a couple of days of making and I've had great success with relatively older ingredients. I have had limited success by removing the frothy mixture from the top of the blender, but even the better mixture at the bottom does not produce great pancakes.

PS: Yes, I wish I'd taken a photo or two but I was so stressed by it happening again I just didn't. Sorry.
I don't have much experience of cooking with gluten free flour so can't comment on any degree to which that might be a factor. I would generally let a pancake batter sit for at least 15 minutes before use to let the flour fully absorb the liquid, that may be less necessary with gluten free flour.

However there are three main things that leap out at me from the description as being possible sources of the problem:


The recipe: pancake batter is quite thin normally, if you push the balance too far towards liquids, the batter can't form a cohesive pancake because the flour mix is too dilute, the bonds can't be formed. It will eventually form a solid, but not until heat has driven off the excess liquid. Your recipe already has a higher proportion of liquid than most UK recipes I've seen, and also less egg for the amount of batter than many. Obviously it works for you some of the time, which leads us to the next point...
Not measuring flour: Your recipe is for a pretty thin batter, that reduces the tolerance within which under-measuring still lets the batter function. I suspect that the times you see what you describe as 'separation' is when there just isn't enough flour to thicken the liquid.
Pan temperature. What you describe as 'fizzing' may be what others would just call sizzling, the mixture hit the hot pan surface and the liquid in it quickly turns to steam, causing the bubbles. This is going to be more pronounce the higher the proportion of liquid in your batter.


A minor thing is that in my experience some thing
s work better if you just whisk them together rather than using the chopping motion of the blades in a blender. I'd put pancake batter in that category, but that may be just personal preference.

I recommend that 


you start measuring the flour to ensure that you achieve a consistent
batter
Use a small amount of batter to test the temperature of the pan before you start making the pancakes proper.
Try whisking rather than blending and resting the batter, though I think these are less likely to make a difference. 


My personal preference would always be to cook pancakes in a buttered pan too. One of the benefits of that, apart from the flavour, is that because butter burns if the pan is too hot, you have to keep the pan temperature lower and that is generally a good thing for pancakes.