First multi-rest mash

I’m getting ready for my first multi-rest mash.
Oktoberfest
5 # Pilsen
5 # Munich
.5 # Med. Crystal
1 # Dark Munich 40 EBC
Hallertauer (60)
Bavarian Lager yeast
Mash Schedule
122 deg 20 min
153 deg 60 min
170 deg

My MLT is igloo 10 gal. with a SS braid, that I’ve used several times for my AG and works fine.

I’m trying to calculate the grain / water ratio and not sure you to do it for multi-rest with this cooler. I usually use 1.25 for my AG.

Do I just want to end up with a 1.25 w/g…
0.75 at 122 deg, 0.5 at 153 deg. ??
0.6 at 122 deg, 0.65 at 153 deg???
Or do I go higher water/grain to get more water?
What do most people use?

Don, I know this likely won't help you for your brew tonight, but have you thought about steam infusion for doing multi-step mashes? It is a very easy alternative to multiple infusions to achieve a multi-step mash (not that there is anything wrong with this). I have a cooler MLT as well, and found this system to work really well.

See these posts for details:
https://www.homebrewtalk.com/showthread.php?t=23127
https://www.homebrewtalk.com/showthread.php?t=25974

After reading alot into this hole multi step infusion mash, i determind it not to be the best style of mash, pretty much because of the question you ask. Do you use less water:grain ration to start and have very thick mash and then on the next infusion you bring that ratio up. Well what if you want a third infusion step, now your mash it probably going to be to thin. So what i have determined is that I dont want to do step infusion mash, but if you read into decotion mash, it solves all the problems when using a cooler. I dough in with what ever water:grain ratio I want (1.25 in your case) and rest at the first temp(122) for 10 mins. Take out about a third (use the equation listed here http://brewery.org/library/DecoctFAQ.html to figure the exact amount out) and heat it up in a kettle of pot or what ever you have to the 153 rest for 15 mins or so. Now bring this portion of the mash to a boil, grains and all. Then add it back to the mash untill the entire mash reaches 153. This way you are raising the temperature of the mash but keeping the water:grain ration the same. I think decoction mash is great for this even though its ment to do something. Things to make sure of, that your mash pH is below 5.7, and that your decoction is thick, not too watery.

Thats what i determinded was best for me when i was in your situation. Plus the decoction will reallllly help develope the maltiness of the oktoberfest

This is one of the nice things about having a MLT you can direct heat or a HERMS/RIMS where you can step the temps. You just do a single infusion to your first rest temp and then you can reach your other temps without thinning out the mash too much.