Extract/Partial Mash IBU Calculations

Discussion in 'General Brewing Discussions' started by Bobber, Nov 13, 2015.

  1. Bobber

    Bobber New Member

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    So I thought I might share a tip that has help me to nail down the IBUs I'm targeting in each of my recipes. When building a recipe I've quite often found that the Tinseth and Rager formulas are drastically different, the difference between a Pale Ale and and IPA really. To help with this, I've found that when using extract, you can alter the ratio of extract added early and late in the boil until the two calculations end up with pretty much the same result.

    I may get this backward, but as I understand it the Tinseth formula accounts for the boil gravity where as Rager does not. So if the Tinseth formula is coming up with a lower value than Rager, you can add a little bit more of your extract as a late addition until the IBUs come close to the Rager IBU value. Basically you are decreasing the boil gravity for your bittering hops and thus increasing the bittering potential. Whether this method is accurate or not I don't know, but at least I'm able to be a bit more consistent.

    Just to illustrate, the recipe below came out to 43.66 IBU Tinseth and 46.40 Rager. The amount of extract I added late was based on keeping the two calculations close. As you alter the ratio, you'll see the values diverge. Anyway, I hope you find this helpful!

    HOME BREW RECIPE:
    Title: #33 - Hoppy Fall Ale

    Brew Method: Extract
    Style Name: American Pale Ale
    Boil Time: 60 min
    Batch Size: 2.5 gallons (fermentor volume)
    Boil Size: 2 gallons
    Boil Gravity: 1.041
    Efficiency: 56% (steeping grains only)

    STATS:
    Original Gravity: 1.065
    Final Gravity: 1.015
    ABV (alternate): 6.77%
    IBU (rager): 46.4
    SRM (morey): 8.69

    FERMENTABLES:
    0.5 lb - Dry Malt Extract - Light (9.4%)
    1.9 lb - Dry Malt Extract - Light - (late addition) (35.8%)

    STEEPING GRAINS:
    2.4 lb - United Kingdom - Maris Otter Pale (45.3%)
    4 oz - German - CaraMunich II (4.7%)
    4 oz - American - Bonlander Munich (4.7%)

    HOPS:
    7 g - Columbus, Type: Pellet, AA: 15.6, Use: Boil for 60 min, IBU: 35.57
    7 g - Centennial, Type: Pellet, AA: 9, Use: Boil for 5 min, IBU: 3.33
    14 g - Crystal, Type: Pellet, AA: 3.8, Use: Boil for 5 min, IBU: 2.81
    7 g - Simcoe, Type: Pellet, AA: 12.7, Use: Boil for 5 min, IBU: 4.7
    7 g - Centennial, Type: Pellet, AA: 9, Use: Dry Hop for 4 days
    14 g - Crystal, Type: Pellet, AA: 3.8, Use: Dry Hop for 4 days
    7 g - Simcoe, Type: Pellet, AA: 12.7, Use: Dry Hop for 4 days

    OTHER INGREDIENTS:
    0.5 tsp - Irish Moss, Time: 10 min, Type: Fining, Use: Boil

    YEAST:
    White Labs - California Ale Yeast WLP001
     

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