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Re: Sugar calculations
On Fri, Mar 8, 2013 at 9:43 AM, Philip Lee <rocketman768@xxxxxxxxx> wrote:
> On Thu, Mar 7, 2013 at 9:12 PM, mik firestone <mikfire@xxxxxxxxx> wrote:
>> In a small word, the brewnote efficiency calculations are rather messed
>> up. I'm using the postboil gravity when I should be dealing with the
>> preboil. I'm trying to unwind this right now but I keep running into weird
>> I am specifically looking at Recipe::recalcBoilGrav() and trying to
>> figure out why the boil gravity (aka, SG) is worried about trub/chiller
>> losses. Trub/chiller loss shouldn't have anything to do with the preboil
>> gravity, should it?
> You'd think it wouldn't have anything to do with it. However, there is a
> nit to be picked...
> BeerXML says the recipe efficiency is brewhouse efficiency, which is
> "to-the-fermentor" efficiency. Meaning, if I have 5.00 kg grain with 76%
> yield (3.80 kg sugar), and my brewhouse efficiency is 70%, I get 5.00 kg *
> 0.76 * 0.70 = 2.66 kg into the fermentor. Now, how would you go about
> finding how much sugar is in the kettle? Since the recipe's efficiency is
> "to-the-fermentor", we can't use that number directly; we need
> "to-the-kettle" efficiency. Since you are always losing some amount of
> sugar at each step of the brewing process, it must be the case the your
> "to-the-kettle" efficiency is somewhat higher than your "to-the-fermentor"
> efficiency. How much more?
> eff_tokettle = eff_tofermentor / (1 - trubChillerLoss/finalVolume)
> To extend the previous example, suppose my final volume is 20 L and I lose
> 1 L in the transfer from kettle to fermentor.
> eff_tofermentor = 0.70
> trubChillerLoss = 1 L
> finalVolume = 20 L
> sugar_kettle = 2.66 kg / (1 - 1L/20L) = 2.80 kg (73.7% efficiency to
> sugar_lost = 1L/20L * 2.80 kg = 0.14 kg
> sugar_fermentor = 2.80 kg - 0.14 kg = 2.66 kg (70.0% efficiency to
> I highly doubt any other software is picking this nit, but it definitely
> exists. You can see for this typical example that all your OG-related
> numbers would be off by about 4% if you don't calculate the kettle
> efficiency to be different from the brewhouse efficiency.
> Philip G. Lee
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> Ah. I was really hoping there was a reason for that, because I couldn't
make heads or tails of the math.
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