Brain hurts, need help

[PoorBoy]

So, I'm playing in excel, pooling together a couple different resources into one place for calculators. I'm running into problems with how to calculate post-mash (pre-boil) target gravity. i.e, if i have 6.5g that i'm boiling down for an hour, with a boil-off rate of 1g/hr, and my target post-boil gravity is 1063, what would my target pre-boil gravity be (so i know how much dme to add if req'd)?

buddy and i are getting ready to go AG BiaB in a week or so, and want to make sure i have all my ducks in a row.

 

[Hang Glider]

http://byo.com/resources/brewing

http://www.tastybrew.com/calculators/

http://beercalculus.hopville.com/recipe

http://www.brewheads.com/calc.php

first 4 hits on Google - "Brewing Calculator"
You can do this, but why? someone else has already done the work - There are even iPhone and Android apps for this.
I understand the desire to figure it out for yourself, (that's why my primary forum is lurking thru DIY) - but if your brain hurts....

 

[PoorBoy]

I visited a bunch of calculators, and they are all great at telling my what my expected OG/FG are, based on xx% efficiency and ##fermentables, but the issue I'm having is getting to the target OG.
If after pulling my biab grains, sparging and squeezing the crap out of them up to 6.5g (i'm using a 30qt pot), what should I want my pre-boil gravity to look like, assuming 1g boil-off and a target OG of 1065? And what's the formula to get there? hopville, brewers friend, they won't tell me. Brewheads has something like it, where i could more or less reverse engineer it...

 

[TyTanium]

See if this helps:

Target 5.5 gallons at 1.063. So 63 gravity points x 5.5 gallons = 346.5 gravity units
346.5 gravity units / 6.5 gallons = 53, so 1.053 preboil target gravity.

If your pre-boil reading is NOT 1.055, or not 6.5 gallons, simply multiply your actual volume by your actual reading (say 6.75g @ 1.049)...so 6.75 x 49 = 330.75
You were shooting for 346.5, but only got 330.75. The difference, 15.75, tells you how much DME to add.
DME gives you 43 points per pound per gallon...well you only need 15.75 points, so 15.75 / 43 = .37 pounds of DME, or ~5.9 ounces.

 

[PoorBoy]

See if this helps:

Target 5.5 gallons at 1.063. So 63 gravity points x 5.5 gallons = 346.5 gravity units
346.5 gravity units / 6.5 gallons = 53, so 1.053 preboil target gravity.

If your pre-boil reading is NOT 1.055, or not 6.5 gallons, simply multiply your actual volume by your actual reading (say 6.75g @ 1.049)...so 6.75 x 49 = 330.75
You were shooting for 346.5, but only got 330.75. The difference, 15.75, tells you how much DME to add.
DME gives you 43 points per pound per gallon...well you only need 15.75 points, so 15.75 / 43 = .37 pounds of DME, or ~5.9 ounces.

that first part is exactly what i was looking for, and i even had it, just fudged my cell numbers in the formula. i could kiss you, if i weren't so fat and hairy.

 

[Brulosopher]

This will help even more: www.beersmith.com

Cheers!

 

[PoorBoy]

I have beersmith on my laptop at home, but i'm at work killing time now. and have two kick-ass calculator to show for it. one that calculates my target pre-boil gravity and makes DME addition recommendations based on my target OG and measured pre-boil gravity, and one for water volumes and kettle size that accounts for displacement
Thanks!

****. i need a beer

 

[DeafSmith]

A perfect application for a slide rule! Sometimes the old technology really is best. You can set the volumes on the D scale and the gravity on the CI scale. Set the cursor hairline to 5.5 on D and move the slide to set 63 on CI under the hairline. Now just slide the cursor to ANY preboil volume on the D scale and immediately read the corresponding gravity under the hairline on the CI scale (6.5 gallons = 53.4 or 1.053). You can also read your total gravity points on the D scale under the C scale index (347).

OK - this was somewhat tongue in cheek, since I realize I'm probably one of the few people here who is old enough to know how to use a slide rule (or maybe even know what one is), much less to actually have one, but I use my slide rule this way on every brew. I can check my preboil volume and gravity and then immediately see what I need to boil down to in order to hit a particular OG. No need to type in any numbers, just slide the cursor to the desired gravity on the one scale and see the corresponding volume under the hairline on the other scale.

 

[PoorBoy]

Bah, I'm not buying more equipment!

Slide rule. Pffffffffft

 

[Hang Glider]

I used to love my slide rule! Had a nice K+E with a leather case...just like this one:

 

[oakbarn]

We use BrewMath, an Iphone app. Does it for me.

 

[DeafSmith]

I used to love my slide rule! Had a nice K+E with a leather case...just like this one:

Hard to tell from the picture, but that looks it might be a 4070-3 ?

My Post Versalog was my constant companion in college and the first few years on the job as an engineeer, until I bought an HP-45 in 1973 or 74. Put the Versalog away and didn't look at it again until about 6 years ago. Got interested in collecting slide rules and now I have somewhere between 125 and 150 from all over the world. Amazingly clever little devices, perfected over a period of 350 years, then made obsolete in the blink of an eye (or should I say, in the blink of an LED ?).