BIAB - correct OG but evaporation less

Discussion in 'General Brewing Discussions' started by NunheadBrewer, Oct 20, 2014.

  1. NunheadBrewer

    NunheadBrewer New Member

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    I hope this is a simple question due a relatively simple answer, as I am new to BIAB (3 so far) and not a scientist!

    I have followed a recipe, and then used an online calculator to work out grain bill and water needed.
    Although the last two times, i have roughly hit the OG stated in the recipe but ended up with around 35-40% more beer than planned.

    What could be factors here?

    It makes me think that if i get the starting water volume correct, the gravity will be really high during the brew and I'd have to water it down (adding more water/volume)?!


    any info would be gratefully received!
     
  2. Ozarks Mountain Brew

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    what size pot do you have and how do you heat it to boil
     
  3. NunheadBrewer

    NunheadBrewer New Member

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    34cm diameter, heating on kitchen gas oven top.
     
  4. Nosybear

    Nosybear Well-Known Member

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    We need the pot's volume. The scenario you describe, making a concentrated wort then diluting it, is common for early brewers. If I understand your problem, you are hitting your OG before boiling, then you are ending up too high after the boil? If that's the case there are two potential problems. First, you are boiling off more water than the recipe anticipates. In this case, it helps to remember that recipes are guidelines, a set of ingredients and sequence of steps that worked for someone on their system. Every system is unique and you have to brew several batches to get to know yours. The problems are browning your wort - the more concentrated it gets, the greater the Maillard, or browning, reaction. You won't be able to produce really light beer but you can get some yummy flavors through what's commonly called kettle caramelization (a misnomer, there's no caramelization going on in the presence of water). Compensate for this by increasing the amount of water in the initial wort or by diluting the final product with water to the gravity you want. The other potential problem is hop utilization, which suffers as the concentration of sugars in the wort increases. Compensate for this by using 10% - 20% more hops in the boil. Diluting the wort is generally not a problem as long as your water is reasonably clean or you've boiled it.
     
  5. Ozarks Mountain Brew

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    your main issue might be the recipe doesn't match what you have for a pot and boil off rate and you didn't evaporate enough, I'm not sure what all you can get to with a trial membership. if you can get to this link you first need to find your boil off rate with the pot your using and fill out this equipment profile, then add your recipe and fiddle with the recipe builder to get the right finished volume say 5.5 gallons so with a small pot you should start with 6.5 gallons or end up with only 5.5 if you do a partial boil

    https://www.brewersfriend.com/homebrew/ ... /equipment

    I think we need your whole process to really tell you what you need to do though just guessing here
     
  6. NunheadBrewer

    NunheadBrewer New Member

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    Nosybear, thanks for your reply. the gravity readings are fine throughout, its is just that the wort isnt evaporating as per the calculations i have got from a spreadsheet. so i end up with more beer (which is fine, apart from when you are fermenting in a demi john one time!!)
     
  7. NunheadBrewer

    NunheadBrewer New Member

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    thanks Ozarks, I am still baffled.
    The link works, but it doesn't give me a boil off rate, it just lets me enter specifics to my set up?
    The recipe builder also doesn't seem to calculate or let me tweak anything?
    New to this site, apart from following recipes, so excuse ignorance!

    I followed the calculator on BIABbrewer.info, to get grain bill and water to add. maybe i need to monitor the boil off rate and amend their sheet?

    it does say 'Evaporation Per Hour* 3.89' , and that you may want to 'tune up; depending on your kettle
     
  8. Ozarks Mountain Brew

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    you have to test the boil off rate yourself and adjust the efficiency and water accordingly, its not the same for everyone
     
  9. Nosybear

    Nosybear Well-Known Member

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    The boil rate will be specific to your setup, pot size, BTUs generated, etc. Best way to find the rate for your system is empirically: Put a known quantity of water in your pot, boil it for a half-hour (or an hour), let it cool and re-measure, the difference is your boil-off rate. In a spreadsheet I wrote for myself to calculate my setup, I have it in gallons per minutes (liters per minute if you use sensible units of measurement) and multiply times the boil time in minutes to get my evaporation losses. If you really wanted to be scientific about it, you'd do a few samples, take the mean and so forth but for homebrewers, one test is probably enough.
     
  10. Ozarks Mountain Brew

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    also the narrower the pot the less boil off, the wider then more boils away, more surface to boil
     
  11. NunheadBrewer

    NunheadBrewer New Member

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    Thanks to both!

    based on my last two, its around 5.5l per hour, strange though that the spread sheet i used had a default of 3.8l per hour, so i should've ended up with less not more beer?!

    I have found another spreadsheet http://pricelessbrewing.github.io/Metric which i will test out next time and see what happens.
     
  12. The Brew Mentor

    The Brew Mentor Well-Known Member

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    It sounds like you're starting with to much water.
    I use approximately 1/10 of a gallon per pound of grain as an absorption rate ( for 10 pounds of grain you'll loose 1 gallon to the grain). This may be slightly low, but it's always easier to add water than to boil it off.
    A typical water assessment would be something like this...

    Wort to fermentor post boil 5.25 gal
    Absorption from 12# grist 1.2 gal
    Boil off rate @ 1 Gal/hour 1 gal
    Kettle/ Tun losses .5 gal
    Total water needed Approx. 8 gallons

    Hope this helps,
    Brian
     
  13. NunheadBrewer

    NunheadBrewer New Member

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    thanks for that, its starting to make sense!
    i assumed it was due to too much water in, but then hitting the correct gravity is still confusing me but i will see what happens on the next brew (end of month)!

    cheers all!
     
  14. The Brew Mentor

    The Brew Mentor Well-Known Member

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    Get you're volumes correct and record the gravity you get. Then you can adjust your brew house efficiency.
    Easy Peasy! :mrgreen:
    Brian
     
  15. Ozarks Mountain Brew

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    if you put in too much water "and you know it" just boil to the correct starting water level and wait to add your first hop till then and you can have a correct 60 minute boil and end up right

    I seem to have this issue from my sparging too much, I get greedy
     

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