Formula For Bitterness

[carpet19]

im brewing recipes from graham wheelers books. does anyone know which formula for bitterness he uses. is it tinseth, rager, or garetz. I am asking as there is quite a bit if ibu difference when using beersmith for calculations. Cheers.

[Aleman]

Grahams is a simple linear calculation, and yet from alpha acid extraction with boil time plots it is more of a polynomial, which is where Rager and Tinseth come in. Personally I find Tinseth to come closest to the results I obtain in my system (From said plots), and using a spreadsheet I have tweaked his formula to make it even closer)

AS Daab says all teh formula is is an estimation of the extracted IBU, and as long as you pick one and stick with it you can adjust you hopping accordingly. (I for instance formulate my recipes to provide 15% MORE IBU than called for as I know that Tinseth in its native form, Promash, produces under bittered beers in my system)

[carpet19]

thanx to daab and tjb, by the way what the hell is a polynomal. am going to stick to tinseth. didnt realise this was so scientific, but i suppose its as scientific as you want it to be. btw, can i just say what an excellent forum this is. dont know, and dont want to know about the science, but my beers taste bloody marvellous.

[Aleman]

I'm Flattered

I do still use a pen and paper, although for a rough idea I can pretty much do the various caclulations in my head (It stops me getting lazy)

For those interested in the Tinseth Formula it can be found here

for those not bothered to click the link the meat of the calculation is here

Code: Select all

IBUs =utilization * mg/l alpha acids

To calculate the concentration of alpha acids you add to the wort:

mg/l alpha acids = decimal AA rating * grams hops * 1000
                  ---------------------------------------
                      volume of finished beer in liters


utilization = (1.65 * 0.000125^(wort gravity - 1)) * (1 - e^(-0.04 * time in mins) )
                                                     (---------------------------- )
                                                     (                4.15         )

Basically a polynomial is a function that generates a curve when graphed. Tinseths graph starts off rising steeply then the steepness tails off as boil time decreases. Graham Wheelers formula produces a curve that is a straight line, and Ragers produces an S shaped curve, which certainly doesn't fit with the results I've obtained with a plot of extracted AA Vs Boil Time.

Tinseths formula isn't complete though as David has commented it assumes that hops added at the end of the boil and steeped contribute no bitterness, which is a patent absurdity. For my part I would bet that you would see a similar curve (With different factors of course ) to the main boil. Of course to take this into account you are looking at having to integrate the various functions to end up with a definitive formula to 'estimate' the IBUs contributed throughout the boil and steeping . . . .Personally I prefer to estimate the IBU contribution of the steeped hops as the thought of the complexity of the mathematical problem makes me reach for a beer to make the headache go away