Homebrewing Newcomer: Question about Strike Water and Pre/Post Boil OG's

Discussion in 'Homebrewing' started by Naked_Batman, Jun 25, 2015.

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  1. Naked_Batman

    Naked_Batman Aspirant (273) Jun 24, 2015 Florida

    Hey guys,

    New to homebrewing and BA, and I have a quick question.

    I'm a BIAB homebrewer (small apartment) and I've completed 2, 1 gallon batches of Beer from kits. Both all grain, but none of them really required any measuring or mathematics and I essentially just followed the instructions. They've turned out so-so but for the next batch I want to really nail it.

    Here's what I understand so far:

    ppg = # gallons of wort extracted x their gravity/lbs of malt used
    efficiency = ppg / the max. extract of the grain bill

    Amount of malt needed to create a beer with a given post boil OG =
    1.) anticipated yield in ppg x recipe volume
    2.) target gravity post boil x max extract for grain bill in ppg
    amount needed in lbs = 2/1

    Here's where I get lost:
    I've read John Palmers "How to Brew" on this subject and he says this:

    "Remember though that this is the post-boil gravity (in regards to determining how much malt to use). When you are collecting your wort and are wondering if you have enough, you need to ratio the measured gravity by the amount of wort you have collected to see if you will hit your target after the boil. "
    http://www.howtobrew.com/section2/chapter12-6.html

    My question is this:
    If the equation to determine the amount of malt needed for a specific post boil-OG is related to the amount of wort I have post boil, how much strike water/starting water do I use to achieve that deisred post boil OG? I don't understand what he was saying about having to create a ratio of the two? Is the amount of malt given by the equation the amount I need to start with when I start mashing in or does it need to be adjusted for the boil?

    Thanks and sorry for the lengthy post . Just new and still getting used to this stuff. Glad that all that college chemistry I thought was useless is starting to pay off. Cheers.
     
    #1 Naked_Batman, Jun 25, 2015
  2. VikeMan

    VikeMan Grand Pooh-Bah (3,067) Jul 12, 2009 Pennsylvania
    Pooh-Bah

    PPG means Points per Pound Per Gallon. It's usually used in regard to the maximum theoretical "points" that can be extracted from one pound of malt (or whatever) in one gallon of water. Let's say Pilsner Malt has a max potential of 38PPG. That means if you extract one pound of pilsner malt into one gallon of water, the maximum theoretical Original Gravity would be 1.038. (Two pounds of malt into one gallon would have a max theoretical gravity of 1.076).

    But you'll never hit the maximum, because your mash efficiency will not be 100%. Let's say it's 70%. Now your one pound of pils malt into one gallon of water will yield a gravity of 1.0266 ((38PPG/1000 x 1 pound / 1 gallon x 70%) + 1)

    Mash Efficiency is actual extraction divided by theoretical maximum extraction. In the above example...
    .0266 / .038 = 0.70 (or 70%) Mash Efficiency

    The amount of starting water is determined by your batch size, your water boil-off rate, your grain wort absorption, your hop wort absorption, and possibly other wort losses. Once you have determined your total water, and you know (or estimate) your Mash Efficiency, you can figure out how much grain you'll need to get your desired post boil OG. (And then readjust for more/less grain wort absorption that goes along with your new malt amount.)

    The pre-boil OG and the post boil OG are inversely proportional to the pre-boil volume and the post-boil volume. Say you have 2 gallons of pre-boil wort @ 1.030 OG. If you boil it down to 1 gallon, the post-boil OG will be 1.060...
    Post Boil OG = Pre Boil OG x (Pre Boil Volume / Post Boil Volume)

    It definitely helps to understand the concepts, but the calculations (including all the loss stuff) can be tedious. Here's a free spreadsheet that some BAs use...

    http://www.beeradvocate.com/community/threads/brewcipher-4-0.294104/
     
    #2 VikeMan, Jun 25, 2015
    Last edited: Jun 25, 2015
    DVoors, Naked_Batman and CurtFromHershey like this.
  3. Naked_Batman

    Naked_Batman Aspirant (273) Jun 24, 2015 Florida

    @VikeMan thanks so much for taking the time to respond! Cleared it up. Thanks!
     
    #3 Naked_Batman, Jun 25, 2015
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