Fahrenheit hurts my brain!
Yep, those steps are going to have a big impact on the finished product.
The first step is ~61*C. That step optimists beta amylase, so produces more fermentable sugars. So that will push a drier beer.
The second step is ~68*C. That's optimizing Alpha amylase more, so produces a fuller body and sweeter beer.
The third step is ~72*C, and does 2 things. The higher temp speeds up both alpha and beta (& starts denaturing them also) to maximize their yield; and it also produces better head retention (by producing more unfermentable oligosaccharides?).
So basically the 68 step produces a full/thicker and sweeter beer, but the previous 61 step should dry it a fair bit to reduce the sweetness and the 72 helps finish it off and give a good head.
Should be a balanced, dry but full beer with a good head!
Fwiw, I'd normally do something like:
55 for 5 mins
63-66 for 40-60 mins
72 for 20-40 mins
78 for 2 mins
I've never done a Belgian Wit, but this worked well on my Saisons and the Belgian ale sitting in my FV ready to bottle.
(The 55 step also helps with head retention)
Hope that helps and apologies for repeating all that amylase stuff if you already knew it - it's as much for anyone else reading this who's learning the ropes :lol:
Edit: tempted to agree w Wiggman. Maybe for your first BIAB, just do a 65 or 66 step for 60-90mins. It should still work well and you can do all the step stuff next time. Step mashing is pretty simple so go for it if you're really keen, but for the first one it might be less stressful to just get familiar w everything else first.
2c