BIAB: adding grains before heating water?
 

Could I add my grains to the water in the kettle and then raise the mix to mash temps? Any advantages or disadvantages?

You'll find this to be very difficult. It will take constant stirring and measuring the temperature to keep from overshooting the temperature. Far better to use a calculator for strike water temperature and mix the grain it.

I've tried to gently add a little heat when my BIAB mash was cooling too much but I ended up with a sudden temperature rise rather than the nice slow one I expected.

I guess you could do it it. I wonder if having the grain at a lower temp than you actually plan to mash at for a while as the temp is rising would create a thinner beer.

Why are you considering this?

I've been doing this since I started BIAB about 2 years ago. Beer turns out fine, but you do need to stir continuously as you approach your target temp or risk overshooting.

I usually add my grains at about 10c below mash temp and stir and heat until mash temp.

Don't need no stinking calculations

I think that some % of the complex carbohydrates would be washed from the grain at the lower temps before the temperature triggered the enzymes that break down these sugars to simple sugars that yeast are able to eat.

I don't know what that % would be, but to some extent, you'd lower your efficiency and produce a lower bodied beer.

I don't know the exact chemisty, just the higher level processes, but I do know that the difference between mashing at 148 and mashing at 156 is a good 5-10% in gravity points due to the same enzyme issues as above, so depending on how long you left your grain soaking in water while you were heating up to your mash temps, I think you'd be surprised how much you'd affect your efficiency, gravity, fermentables, and unfermentable complex sugars left over in your final beer.

I wouldn't mess with it.

I would say just get slightly above the mash temp, add grains while still heating (temp will drop) and stirring, checking temps, and be prepared to cut the heat as soon as you reach the mash temp.

Or, you could just let Beersmith, etc. tell you what strike temp to reach, then add grains...like most people probably do.

any advantages/disadvantages depend on what temp you're talking about starting at and how quickly you'll be ramping up.

neither of these things are correct.