How to convert a recipe to partial mash

[bwgolling]

I suppose my question has been asked and answered, but I cannot find it, so here goes.
Is there a formula to convert an all grain recipe to partial mash, or is just a guess-timate?

 

[MJDore]

Plop down $20 for Beersmith and make life easier. It will be the best $20 you've ever spent on homebrew equipment/necessities.

 

[Yooper]

The easiest rule of thumb is that 1 pound grain = .75 pounds LME- .6 pounds DME.

So, for a grain bill like this:

10 pounds two-row
1 pound crystal 60L

you could do:
7.5 pounds LME
1 pound crystal 60L

or

6 pounds DME
1 pound crystal

or
5 pounds two-row
3 pounds DME
1 pound crystal 60L

or

2.5 pounds two-row
1 pound crystal 60L
4.5 pounds DME

etc.

You can use DME or LME to "make up" the fermentables, in however much you need depending on how much grain you can mash. Keep all the specialty grains the same, and use two-row for the base grain. Try to mash at least as much base grain as you do specialty grains- for example, for a recipe with 1 pound crystal and 1 pound oatmeal, try to mash at least 2 pounds base malt for a total of 4 pounds, or more if you can.

 

[USMCYoder]

Plop down $20 for Beersmith and make life easier. It will be the best $20 you've ever spent on homebrew equipment/necessities.

Or if you are on a Mac like me, you can play with a recipe in BeerAlchemy. It does pretty much the same thing.

 

[chiefbrewer]

Here is my formula

Start with an all grain recipe. Then figure how many pounds of grain your partial mash system can comfortably hold (mine is 5.5 to 6 pounds)

Add up all your specialty grains and figure up how much 2-row (or whatever the bulk of the grain bill comes from) you can use to keep your grain bill at the proper weight.

Then figure up your gravity points, and determine how many points you need to hit your target gravity.
Then figure how much extract you need to hit it.

Example:
American Pale Ale

10# Pale Malt
.75# Crystal 20
.5# Biscuit
.5# Victory
.25# Crystal 120

12 total pounds of grain...taret OG 1.054

So you would use all of the specialty grain wich gives you two pounds...then fill your 5.5 pound partial bill with the Pale Malt
New Grain bill:

3.5# Pale Malt
.75# Crystal 20
.5# Biscuit
.5# Victory
.25# Crystal 120

But this only gives you about 1.024 so you need about 30PPG from your extract
Considering DME gives you about 43ppg, some quick math tells you that 3.5 lbs of DME will get you real close

This metod works for me.
Edit: As was stated before make sure at least half your grain bill is a base malt...otherwise you won't have enough conversion power for the mash.