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Tinseth Hop Calculation Help

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NorthernIke:
I'm sick of looking up hop utilization numbers when building recipies.  I use a spreadsheet that I built for my brewing "software".

I need some help building an equation in Excel.  I use the Tinseth formula, and on his page on of the stated factors is "boil time factor".  This is determined by this equation:

The Boil Time factor accounts for the change in utilization due to boil time:

Boil Time factor = 1 - e^(-0.04 * time in mins)
--------------------------
4.15

My question is what does "e" refer to in the above equation?  How do I program this into Excel?

Here is Tinseth's page where I got the formula:  http://realbeer.com/hops/research.html

Thanks!

NorthernIke:
From Wikipedia: http://en.wikipedia.org/wiki/E_%28mathematical_constant%29

The mathematical constant e is the unique real number such that the value of the derivative (slope of the tangent line) of the function f(x) = ex at the point x = 0 is exactly 1.[1] The function ex so defined is called the exponential function, and its inverse is the natural logarithm, or logarithm to base e. The number e is also commonly defined as the base of the natural logarithm (using an integral to define the latter), as the limit of a certain sequence, or as the sum of a certain series (see the alternative characterizations, below).

e is one of the most important numbers in mathematics,[2] alongside the additive and multiplicative identities 0 and 1, the constant π, and the imaginary unit i. (These are the five constants appearing in one formulation of Euler's identity.)

I guess I'm no Mathlete!  I'm going to try and plug this into Excel...maybe it's smarter than me...

NorthernIke:
Thanks to Wikipedia..."e" can be described as:

2.71828182845904523536

This seems to make the Excel formula work like a champ!  Maybe this will come in handy for someone, someday...but probably not!

a10t2:
You can also enter it exactly (or at least, to a whole lotta digits - I don't know if Excel uses a stored value or not) by using the exp() function.

hopfenundmalz:
Remember that your input data will be 2 sig. figures.

Don't quote your output IBU's to 12 decimal places.   ;)