Yesterday I went down to my homebrew retailer, planning on buying a simple screen/valve assembly for a cooler. No go. He didn't have any of THOSE left, however he did have an assembly to use an 8-gallon pot as a lauter tun. So I stopped by the hardware store, purchased a step drill, modified the pot for a valve, screen filter, and thermometer (also a purchase @ the HB store), but not before I had walked out of the homebrew store with the ingredients for a Belgian Dubbel and an extra fermentor:

1 lb Briess American Dextrin (carapils malt) 7.5 lbs Muntons English Maris Otter Malt 0.1 lbs Weyermann German Dehusked CaraFa II 0.5 lbs Dingemans Belgian Aromatic Malt 1 lb Dingemans Beglian Special B 1 lb candi sugar 1 lb honey (he had this AWESOME stuff called "Meadowfoam", which is truly delicious, to the point where I may make some meade from it) 1oz Brewers Gold pellets (60 min) 1/2 oz Hallertau (20 min) 1/4 oz Hallertau (10 min) Wyeast #1214 Belgian Abbey Yeast

I came out with a 1.030 boil gravity. Adjusted for temperature, this was closer to 1.045. After adding the candi sugar and honey along with all the other elements in the boil, I was down to about 4 gallons due to some trub and some substantial boil-off. @ the suggestion of my HB retailer's instructions, I added a gallon of water. My OG was then 1.052. Was diluting a bad idea? How can I allow for boil-off?

  • 1
    What was your target OG? Reply as a comment to this. Then I'll craft an "answer".
    – brewchez
    Mar 30, 2010 at 18:29
  • What was your target final volume? Mar 31, 2010 at 16:47
  • Sorry forgot I posted this question. The typical range for the style is 1.068-1.076. My target final volume was 5-5.5 gallons. Going to try a AG Wit this Saturday, but I'm going to use brewing software...leaning towards Beer Tools, as it seems like Promash and BeerSmith are a little obtuse/difficult to work with. Thanks for your help-
    – FrankieSez
    Apr 26, 2010 at 14:29

1 Answer 1


Get to know your system

Starting gravity is one measure that helps you produce consistent beers. Suppose you made this beer again with the same ingredients, using the same process. All other things being equal, you should hit the same OG. Ferment the two batches the same way and you reproduce the original beer.

It is not necessarily an indicator that you followed the recipe correctly. Recipes are formulated for a generic brewing setup. The creator may be using his or her own system as a reference and knows it produces beer at the same efficiency every time.

Before you start worrying about hitting recipe gravities, get to know your system and the process. One good question to ask is where do I lose water? Leaving sweet wort behind in your mash tun will lower your efficiency.

So I screwed up. What do I do about it?

Relax, don't worry. This is your first all-grain batch.

Instead of chasing every bit of efficiency in your system at first, spend your time discovering how your system performs. Getting the process down and understanding what is going on will eventually lead to better efficiency.

La dee da, where's the concrete advice?

Okay, here you go:

Perhaps more important is pre-boil gravity

Once you are done boiling the options for hitting OG and maintaining hop level are limited. Boiling off more volume to raise the gravity also concentrates the hop flavors and drives off aroma. Adding water to lower the gravity and raise volume dilutes hop flavor and bitterness.

If you hit the wrong pre-boil gravity you can fix it before starting the hop schedule.

The pre-boil gravity, along with volume, will tell you the final gravity.

Gravity Units = Volume * Gravity Points

Gravity Points = 1000 (SG - 1)

Assuming you add no sugars in the boil their weight will not change as water is driven off. From your description, it sounds like you started with, maybe, 5.75 gallons at 1.045 pre-boil. Your sweet wort contains 258.75 "gravity units" (volume * points, 5.75 * 45 = 258.75). At the end of the boil the volume will be different, but the gravity units will not. Dividing the GU (258.75) by final volume (4) gets you to 1.064, which you diluted to 1.052 in 5 gallons (4 * 64 / 5 = 52).

Bah, numbers. Get to the point already

When you get a recipe (or create one yourself) work backward to the pre-boil numbers, and try to collect the right volume and gravity.

For example, on my system I collect 12.5 gallons and after a typical 60 minute boil I'll hit my target 10 gallons. My pre-boil gravity will always be about 80% weaker than my original gravity because of this. I collect sweet wort until I've hit the volume and adjust my gravity if necessary.

A good read: How Do You Calculate Original Gravity

  • Fantastic answer, sir! I second the notion that working backwards from pre-boil volume and gravity is the best way to dial in a recipe after you know the system's mashing efficiency (assuming a standard mill every time) and boil-off rate.
    – BoilerBrad
    Oct 29, 2015 at 13:21

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