Welcome to the forum kartoffel and congrats for jumping into all-grain ,

I think the main worry with the above plan is that too much of your wort won't be seeing the full length of the boil. A boil of proper lenght is important. There's a few other options...

1. Perhaps make 2 bags up and simply do two full-volume brews side by side with half the ingredients in each. This would make things easy. Having two rigs side by side (and two small fermentors) might also allow you to do some interesting experiments.

2. You could swap your bag from one kettle to the other. eg Mash for 20 minutes in kettle 1 and then for 70 minutes in kettle 2. I really don't know about this though. The first option sounds easier and more versatile to me.

3. Another option would be to do as you say except pull the bag from kettle 2 after mashout and then just boil this diluted wort. Both this and option 2 above will throw our hop figures out a bit - they'll be hard to calculate unless you mixed the wort between the two kettles until their og's matched which would be pretty messy.

So, to me it seems that you have two kettles and two burners. All you need is one more bag and you have an easy (and interesting) set up.

There could be other ideas on this but I think keeping it as simple as possible is a pretty good approach.


PP

In your case, you're using a kettle that is easily large enough for a full-volume boil, just not quite large enough for a full-volume mash. There's an even simpler method that I use (I brew ~3.5 gal post-boil batch sizes in a 5 gal kettle on my stove top). Since your kettle is large enough for a full-volume boil, you could sparge with enough water to get you to your proper pre-boil volume. There shouldn't be a need to continue to add water throughout the boil. In my case, I don't sparge at all. I figure on a lower efficiency when determining the grain bill, mash with as much water to fill my kettle to the brim, heat the mash to mash-out temps, pull the bag, and just dilute to the proper proper pre-boil gravity (or volume, whichever you prefer). Sometimes I'll have the top-up water heated to boiling in another pot (if I think about it in advance).

kartoffel wrote:If it is greater than my anticipated OG I can use the calculator to water it down. Seems like I would have more than enough left over at the end and usually wouldnt mind a few points over. If for some reason it was a few points under then don't worry about it, it will still taste great?

I feel like that's a decision that depends on the situation. The easiest thing, in my opinion, to do (if you're concerned with hitting your anticipated OG) is measure the gravity several times throughout the brew session. Why? It gives you more time to adjust things.

Let's say you finish the boil and your OG is way too high. Your options are to 1) leave it as is, or 2) dilute with water. To be absolutely certain that your top up water is sanitary, you should first boil the top up water, chill it, then add it to your wort. That's a lot of extra work. Sure, you could skip boiling, but then you MIGHT be contaminating your wort.

But if you're monitoring the gravity as your go (taking gravity readings pre-boil, 30 min to flameout, flameout, etc.), you can add water straight from the tap into the boiling wort to dilute it (or add DME to increase the gravity if its too low).

If, for whatever reason, you're still missing your OG, then just leave it. I don't feel like its worth messing with (in my opinion).