[bluesman]

I scale my recipes in an effort to achieve the same end product.  By that I mean the same OG,  FG,  IBU's,  ABV,  color ,  etc...

Boy, did I read that wrong at first glance.  I took it that you scale all your recipes (ie. APA, Stout, Pils, etc.) so that they all end up with the same OG, FG, etc.   

and I wasn't drinking beer while I conjured up that thought...imagine that. 

[bluesman]

I scale my recipes in an effort to achieve the same end product.  By that I mean the same OG,  FG,  IBU's,  ABV,  color ,  etc...

For the grain bill I adjust the weight while keeping the same percentages.  Hops are scaled by keeping the IBU's the same.  Yeast is adjusted by unit volume and OG as per mrmalty.

Water is adjusted in accordance with the final volume desired. 

Starting volume = final volume + grain absorption + evaporation (boil-off)

Thanks dude.  You explained what I was trying to say much better than I did.

Every now and then I find my feet. 

[tygo]

Good idea....I'll play around with that.  But I hope they'll change it, anyway!

Yeah, that would be nice.  I was playing around with it a little tonight.  Under evaporation rate in the equipment setup it says "5-15%" next to the field.  But that's just a recommendation.  You can put whatever value you want in there.  For my next brew, assuming it's not too humid, I've got that set at 23% to achieve 2.5 gallons of boil-off for a 75 minute boil (yeah, that's a lot; I've got a wide kettle).

[thcipriani]

I feel that gallons per hour is the only righteous way to keep track of my boil-off rates since, given the diameter of my kettle and the intensity I like to see in my boil, I tend to boil off 1 gallon per hour regardless of whether there are 7 gallon of wort in my pot at the beginning of that hour or 7.5 gallons of wort in that pot. Obviously 1 gallon is a different percentage for every batch size depending on whether I'm doing a 90min boil (and I start with 7.5 gallons) or a 60min boil (and I start with 7 gallons). I think the only time I've ever seen anything that I felt was substantial that quoted boil off as a percent was:

The most widely used indicator is the percent evaporation that takes place in the boil (Narziss, 1992). With standard boiling systems, a general rule is that the volume reduction be at least 7%. However, it has been show that evaporation rates above 12% may produce level 2 heterocyclics, leaving vegetal malt tones that are accompanied with some astringency. A wide range of level 2 and 3 heterocyclics is possible once evaporation rates exceed 15% As already stated, the flavor of the finished beer will determine the extent to which this effect is relevant

- Fix 1999
To me it seems that a 15% volume reduction over the course of a single hour's time boiling would be more significant to a commercial brewer than to a home brewer but that quote is verbatim so take it with as many grains of salt as you feel necessary.

I've got that set at 23% to achieve 2.5 gallons of boil-off for a 75 minute boil (yeah, that's a lot; I've got a wide kettle).

That seems like quite a bit off boil off. What is the width of the kettle that you use? Remember it's not the size of your kettle it's the motion of your wort 

[tygo]

My 10 gallon kettle is 15 inches wide.  The new one I just picked up is a 15 gallon that is 18.5 inches wide but I haven't taken that out for a test drive yet.  I'm going to work on keeping my boil just barely roiling to hopefully bring that evaporation rate down some.

[jgourd]

It makes sense to me to scale in terms of ingredient percentages.  A recipe that calls for 90% 2-row pale and 10% crystal 60 works for any batch size (the amount you want to collect in your fermenter).  So whether you want to make 5 gals or 10 gals, you still use 90% 2-row pale and 10% crystal 60.  But scaling is inherently dependent upon your batch size (the amount you want to collect in the fermenter), the desired estimated OG, your brewhouse efficiency, and the intricacies of your system (e.g. losses in your system, evaporation rate, etc).

In my system, I lose 0.25 gals due to mash/lauter tun deadspace.  I also lose 0.75 gals due to trub losses (hop absorption and leftover wort in the keggle and counterflow chiller).  I also go with an evaporation rate (in gal/hr) as opposed to percentage since evaporation really has nothing to do with the boil volume but rather with your equipment (surface area, heat source, etc).

In terms of hops and bitterness, IBU calculations are dependent upon the estimated OG and batch size.  If you scale a recipe, the OG will remain the same but the batch size will change.  It becomes simple to change the IBU calculation to estimate the increase (or decrease) in hop amounts.  In then end, whatever you scale your batch size to, you'll scale your hops to.  For our pretty small batch sizes (less than 20 gals), even hops scale linearly.

I can review the calculations if you wish, including a simple way to scale batches by providing OG, batch size, brewhouse efficiency, and ingredient percentages.

[Steve]

I concur with scaling using percentages of the fermentables. if you double 60% one of your fermentables. it's still 60% of the total.  That's Zen (or B.S.!)

[beveragebob]

"Starting volume = final volume + grain absorption + evaporation (boil-off)"

+1
and don't forget any equipment losses.