How can I brew different plato at same tank??

We're to assume that your mash tun doesn't have the volume to hold grain for a 21 plato beer?

You have a few options:

You can add malt extract into the boil kettle after you get your runnings to ramp up your preboil OG

You can make a smaller batch of beer. If you typically make 5 gallons of 11 plato beer, you can make 2.5 gallons of 22 plato beer.

You can boil down your wort. It's common, (and unstyleistic), to many Scotch beers.

Invest in a larger mashtun. A cooler and a ball valve start at about $50 and go up from there. One of the advantages of using a cooler for a mashtun is that it's still a cooler. It's officially a multitasker.


Ref the calculator "Can I Mash It?" at the bottom:
https://www.rackers.org/calcs.shtml

 

I really like the small batch option, because, who really wants to drink 5 gallons of a buttkicker at 20-something Plato?

You can also plan to sparge a heck of a lot more, in multiple batches (two or three) or fly sparging (continuous), and boil for a very long time, like 3 hours or something, to keep your efficiency high so that you don't need like 22-23 pounds of grain for 5 gallons, as that's impossible to fit in a lot of mash tuns.

 

https://www.beeradvocate.com/community/threads/bigger-mash-tun-bad-idea.487698/#post-5267188
http://howtobrew.com/

 

More options: Add sugar . . . no this is not cheating and it does not make your beer sweet . . . just ask any Monk you run into.

Decoction for the final infusion; if doing a mashout (or batch sparge), consider draining the liquid after mashing is complete, then boiling and adding back to raise temp of mash. Yes this works and it ain't hard.

A smaller crush; this increases efficiency which is the same as making the mash tun larger. With your own grain mill keep reducing the crush until your sparge is stuck . . . that'll be your limit.

 

I do. You get a good recipe and it'll keep for 3 or 4 years. It doesn't ever last that long, but hey!

 

You could do a double mash day and use the first wort runnings for the 2nd mash water.

Never tried it but sounds interesting.

 

This is how Grampus was brewed by the late lamented Pretty Things. And I guess also Barbapapa and Our Finest Regards.