Lactose Effect on FG

Discussion in 'General Brewing Discussions' started by Steve SPF, Apr 27, 2021.

  1. Steve SPF

    Steve SPF Well-Known Member

    Joined:
    Jun 28, 2019
    Messages:
    450
    Likes Received:
    504
    Trophy Points:
    93
    Morning all,

    Gave myself a minor heart attack yesterday thinking my oatmeal stout had stalled/stopped at 1.020 when I was expecting 06-10 but then remembered the lactose!

    Is there a calculation to help me figure out how much 1kg of lactose would add? Also, as it's added at the end of the boil, what effect will it have on OG as well as FG?

    Steve
     
  2. dmtaylor

    dmtaylor Active Member

    Joined:
    Dec 29, 2018
    Messages:
    56
    Likes Received:
    101
    Trophy Points:
    33
    Location:
    Two Rivers, WI
    Home Page:
    Lactose should add to both the OG and the FG roughly 340 gravity points per kg per liter, post-boil volume (I converted this from the American standard of about 41 ppg, which is points per pound per gallon).

    So, 1kg in say a 19L batch should add 340 / 19 = 18 points to both the OG and FG. Or if you made 38L, then you've added 9 points, etc.

    When you use lactose, it might be best to totally ignore the lactose in any recipe calculations, then after the recipe is designed, add these numbers to both the OG and FG. For example: Let's say you wanted to brew 38L at an OG of 1.069, and the estimated attenuation of your yeast is 75%, and you're going to add 1kg lactose to the boil. Then you know you could design your recipe for 9 points lower, for an OG of 1.060, because you know you'll add 9 more points in lactose at the end. And then with 75% attenuation of the regular sugars present, you can expect an FG of about 1.015 (60 / 4). But finally, with additional lactose, you'll add 9 points to both the OG and the FG, for an OG of 1.069 and FG of 1.024.

    It's a little complicated but not too bad. Hope this helps.
     
  3. _Stephen_

    _Stephen_ New Member

    Joined:
    Mar 20, 2021
    Messages:
    14
    Likes Received:
    10
    Trophy Points:
    3
    I did this as well the first time I used Lactose lol.
     
  4. Donoroto

    Donoroto Well-Known Member

    Joined:
    Jun 21, 2020
    Messages:
    863
    Likes Received:
    1,196
    Trophy Points:
    93
    Occupation:
    Retired Engineer
    Location:
    Atlanta
    So basically lactose isn't fermented. Right?
     
  5. _Stephen_

    _Stephen_ New Member

    Joined:
    Mar 20, 2021
    Messages:
    14
    Likes Received:
    10
    Trophy Points:
    3
    Correct but it still effects your gravity reading even though it won't contribute to ABV.
     
  6. Josh Hughes

    Josh Hughes Well-Known Member

    Joined:
    Apr 7, 2020
    Messages:
    1,535
    Likes Received:
    3,460
    Trophy Points:
    113
    Gender:
    Male
    Occupation:
    Teacher
    Location:
    KY
    #6 Josh Hughes, Apr 27, 2021
    Last edited: Apr 27, 2021
    Funny timing I checked my gravity today (10 days) on a milk stout. Supposed to be at 1.018 it was 1.022. I’m going give it a few more days. Sample tasted great but hate to bottle early cannot reminder if my FG was high last time I brewed this. I’m using US05 this time, i used S04. OG of 1.064. Yes unfermentable
     
  7. dmtaylor

    dmtaylor Active Member

    Joined:
    Dec 29, 2018
    Messages:
    56
    Likes Received:
    101
    Trophy Points:
    33
    Location:
    Two Rivers, WI
    Home Page:
    It's close to finished, but with US-05, maybe not yet. How much lactose in how big a batch? If about a pound in 5 gallons (pretty typical) then I think it could come down close to 1.018. But really depends on recipe. And what was your mash temperature and total mash time?
     
  8. Josh Hughes

    Josh Hughes Well-Known Member

    Joined:
    Apr 7, 2020
    Messages:
    1,535
    Likes Received:
    3,460
    Trophy Points:
    113
    Gender:
    Male
    Occupation:
    Teacher
    Location:
    KY
    8% lactose. 2 gallon batch. Mashed at 151. Fermented mid 60s
     
  9. dmtaylor

    dmtaylor Active Member

    Joined:
    Dec 29, 2018
    Messages:
    56
    Likes Received:
    101
    Trophy Points:
    33
    Location:
    Two Rivers, WI
    Home Page:
    Yeah I think it might still come down a couple more points, hopefully. Waiting a few days is wise.
     
  10. Josh Hughes

    Josh Hughes Well-Known Member

    Joined:
    Apr 7, 2020
    Messages:
    1,535
    Likes Received:
    3,460
    Trophy Points:
    113
    Gender:
    Male
    Occupation:
    Teacher
    Location:
    KY
    That’s what I figured. Thanks. Not used US05 since last summer
     
  11. Nosybear

    Nosybear Well-Known Member

    Joined:
    Jul 16, 2012
    Messages:
    9,548
    Likes Received:
    6,881
    Trophy Points:
    113
    Location:
    Aurora, CO, USA
    It should be the same as any other sugar, about 46 ppg (can't do the metric conversion in my head). Its effect on OG and FG will be the same since it doesn't ferment.
     
  12. Minbari

    Minbari Active Member

    Joined:
    Mar 31, 2021
    Messages:
    114
    Likes Received:
    102
    Trophy Points:
    43
    Gender:
    Male
    Occupation:
    fuel hauler
    Location:
    STL
    Everything I have read confirms this. Lactose does not ferment
     
    _Stephen_ likes this.

Share This Page

arrow_white