Bug in apparent attenuation calculation#147

Hello,

I think there is a bug in the recipe apparent attenuation calculation.
With an OG of 1.049, yeast with 78% attenuation, it gives me an FG of 1.007.
Using the calculator an OG of 1.049 and an FG of 1.007 gives me an attenuation of 85,6% wich is true in my opinion.

Hi Sebastien, thanks for the feedback. We will investigate and get back to you on this issue.

Hi Sebastien

So with the standalone calculator, the calculation is based on the formula
Attenuation = ((OG-FG)/(OG-1))*100)

However, this calculation does not take into account the mash temperature. In the Grainfather recipe creator, we have a ‘Brewers window’ which is between 62.5 and 72.50C. We then have a centre point in this range occurring at 67.50C any mash temp that is conducted in this range is then subjected to an adjustment factor based on if it is above or below 67.50C (below 67.5more fermentable, above 67.5 less fermentable).

attenuation = attenuation - 0.0225 * (lowest Mash Temp - 67.5) Based on your image of the recipe creator id estimate that your mash temperature is 660C if I work backwards

Based on the estimated FG will change significantly between 62 and 63 due to the edge of the brewer window being 62.5. The brewer’s window is set at 62.5 due to the coefficient(+/- 50C) applied to the middle value of 67.5. The results of the different studies done by Michael Lewis and Tom young 2002 and Palmers (Lewis & Young, 2002) (Palmer, 2017) work led us to use 62.5 as this was the midpoint in the edge between the two studies, this is also the same edge many of our competitors use.

As for the ‘time at different mash temperatures’ affecting fermentability. The calculations get complicated very quickly with multiple mash steps, so we try to keep it as simple as possible. For this reason, we use the mash step with the lowest temp in the range of 62.5˚C to 72.5˚C when calculating the FG. If a recipe has it’s main mash step (Beta-amylase) just outside the range at 62˚C and, it’s secondary mash step (Alfa-amylase) in the range at 72˚C. Then for this example, the calculation is run using the secondary mash step temp. However, by changing the first mash step to 63˚C then puts the primary step in range and the calculation for FG would be run off the primary mash step.

The Real attenuation in the standalone calculator take the worse possible result based on the fermentability of malt extract hence this lower than the yeast attenuation.

Please let us know if you have anymore questions.