How to know what Pre-Boil Gravity to hit

[Zandrello]

Hello all,
I am doing my first All-Grain batch today. I have been brewing for about 1.5 years, have all the necessary equipment (finally), and feel that I'm ready.

One question I have is, when I'm doing the Vorlauf, and sparging and whatnot, how do I know what my Gravity should be? In other words, when am I "DONE" Vorlaufing??

I know the "general" signs like, "when it's running clear, you're good", but I don't wana be that vague, and just assume, b/c I've heard of plenty of people just assuming like that, and ended up with a lower than expected gravity. I want to be as efficient as possible.

I know there are tools and whatnot like Beer smith to help with estimations and percentages, but I don't have the money to spend on Beer Smith right now...

 

[Thedutchtouch]

You need to know your boil off rate, and your target final gravity. Using these numbers you can figure out your needed pre-boil volume. Remember to account for any volume left behind with trub (if you're not a "dump it all in the fermenter"brewer)

 

[Paradigm]

Gravity readings are different at different temperatures, because it's just measuring water density. I'm sure you know this, but be sure to be applying the proper offsets when measuring your gravity. Even pre-boil temps are going to be much higher than actual fermentation temps.

I would like to know this as well, though it feels a little too "guess-y" for me to worry about it. Your boil-off rates and break residue / trub are going to vary.

 

[duboman]

Every grain you use will have a potential extract value associated to it, usually somewhere between 1.034-1.036 or 34-36 gravity points per pound. so if you were to do an all Maris using 10 lbs of maris at 1.035 or 35 points you would yield a potential 350 gravity points and then divide this by batch size. so 350/5=70 points per gallon (PPG)

If you assume a 70% efficiency then your 70 points would be reduced by 25% or 1.052 estimated OG for the batch. Generally the preboil gravity is 7-10 points less than the estimated OG due to the concentration of the boil over 60 minutes.

This is by far very over simplified but the basics involved. Efficiency has more to do with various factors such as mash pH, crush, hitting volumes, etc. WHile you may not be able to afford BeerSmith right now, if you do not have "How To Brew" by Palmer I would highly recommend it. It has everything you need to calculate and understand all grain brewing and will prove to be a valuable resource throughout your brewing career.

Here is a link to the online, dated, free version: http://www.howtobrew.com/sitemap.html

 

[Zandrello]

You need to know your boil off rate, and your target final gravity. Using these numbers you can figure out your needed pre-boil volume. Remember to account for any volume left behind with trub (if you're not a "dump it all in the fermenter"brewer)

Well my Target OG after the boil and everything of course is 1.049 ish. Recipe says 1.049, so anything there or slightly higher, I'm happy. So should my pre-boil gravity be much HIGHER than my Final Gravity? Or LOWER?

 

[Zandrello]

Generally the preboil gravity is 7-10 points less than the estimated OG due to the concentration of the boil over 60 minutes.

This is by far very over simplified but the basics involved. Efficiency has more to do with various factors such as mash pH, crush, hitting volumes, etc. WHile you may not be able to afford BeerSmith right now, if you do not have "How To Brew" by Palmer I would highly recommend it. It has everything you need to calculate and understand all grain brewing and will prove to be a valuable resource throughout your brewing career.

Here is a link to the online, dated, free version: http://www.howtobrew.com/sitemap.html

Aah, just saw your comment. So if my target OG is 1.049, then my Preboil gravity (after vorlauf / sparging) should be around 1.056-59 then??

I do not own Palmer's book, but I am a HUGE fan, and plan on buying it ASAP. I do own "Radical Brewing" by Randy Mosher. GREAT BOOK. Although, I am not all the way through it yet.

 

[duboman]

No, backwards math, if the OG is 1.049 your preboil would be 1.039 or thereabout. Concentration the wort and boiling off water would then RAISE the OG.


Sent from the Commune

 

[Zandrello]

No, backwards math, if the OG is 1.049 your preboil would be 1.039 or thereabout. Concentration the wort and boiling off water would then RAISE the OG.


Sent from the Commune

Yes, I misread, sorry!! That makes sense, after sparging and whatnot, the volume of water versus the amount of sugars is much higher, then of course boiling and evaporating water during the boil would make the sugar concentration higher. gotcha.

Thanks guys I think I'm ready! By tonight, my yeast starter will have been spinning away for about 40 hours. Gonna brew, and pitch those strong, ready-to-fight yeast!

 

[Zandrello]

OH! Also, btw, I checked out BeerSmith's website, and they actually offer a 21 day FREE TRIAL for the new version (2.2 I believe)!! So I'm definitely gonna download that this evening, and use it to assist me in my first All-Grain brew. I'll def plan on buying it before my next brew though, I know it's a GREAT tool. Thanks again!

 

[GotPushrods]

Pre-boil gravity target = [(post-boil gravity target) * (post-boil volume target)] / (pre-boil volume target)

That's it, assuming you are hitting your volumes. If you come in a little low, you can add DME, boil longer for a smaller batch, or chalk it up to a learning experience. If you are high, you can add water to end up with a slightly larger batch and leave some behind.