What's the point of measuring pre-boil gravity? I'm using a refractometer and would like to improve the accuracy of my system. I understand that adjustments can be made (adding DME or water) at that point, but how do you know adjustments are necessary? Most recipes I've seen indicate a target OG, not pre-boil. Am I missing something? (Obviously, I am.)
Measuring pre-boil gravity
- Thread starter Buffman
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a recipe can include a pre-boil gravity depending on what software generated the recipe.
i think many recipes posted here don't include that info because a lot of it depends on your system. I might get 5% more evaporation during my hour long boil, which would give me a higher OG post-boil if I had the same gravity and wort volume as another brewer who had 5% less evaporation.
that's my take on it. I know beertools.com free version gives me pre-boil OG options.
i think many recipes posted here don't include that info because a lot of it depends on your system. I might get 5% more evaporation during my hour long boil, which would give me a higher OG post-boil if I had the same gravity and wort volume as another brewer who had 5% less evaporation.
that's my take on it. I know beertools.com free version gives me pre-boil OG options.
kanzimonson
Well-Known Member
Probably the most important reason to measure pre-boil is to figure out how well you did, efficiency-wise. I usually get 75% efficiency, but sometimes when I make batches that don't require as much grain, I get upwards of 78%. But I still make the recipe planning for 75. So I measure the pre-boil gravity to determine if I can make a 5.75gal batch instead of the 5.5 I was planning (or whatever). Of course, you also have to adjust your hops if you do this.
WorryWort
Well-Known Member
I think it is crucial for any measure of consistency and/or balance. But if you don't care about repeating recipes, or about the balance of malt and hops in your beer than I guess it doesn't matter.
If my pre-boil gravity comes out low, I add extract to raise it. Or, I can adjust the hops downwards (or upwards if I missed high) to ensure that I have the same balance I originally intended.
For example if you were brewing a barley wine at 1.090, and it came out at 1.110, then you'd want to add more hops to balance that large difference. Otherwise the beer will be sweeter tasting, or more malty than you intended.
Pre boil gravity is only truly useful if you know your pre-boil volume, otherwise you won't be able to predicted the OG, post-boil. Recipes should give this, in my mind. It speaks to how long and how vigorous your boil - I collect more wort for Pilsners, because I boil off more.
If my pre-boil gravity comes out low, I add extract to raise it. Or, I can adjust the hops downwards (or upwards if I missed high) to ensure that I have the same balance I originally intended.
For example if you were brewing a barley wine at 1.090, and it came out at 1.110, then you'd want to add more hops to balance that large difference. Otherwise the beer will be sweeter tasting, or more malty than you intended.
Pre boil gravity is only truly useful if you know your pre-boil volume, otherwise you won't be able to predicted the OG, post-boil. Recipes should give this, in my mind. It speaks to how long and how vigorous your boil - I collect more wort for Pilsners, because I boil off more.
Touristbob
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Once you know what your pre-boil gravity is and what pre-boil volume you collected you can accurately predict your OG. Using ((pre-boil gravity-1) * 1000 * pre-boil vloume)/post boil volume. For instance, if your prebiol gravity was 1.040 and you had 8 gallons collected, your original gravity should be 1.058 if you have 5.5 gallons after the boil. You can then use this information to add water or dme to increase or lower your gravity to reach your target gravity before you even really start the boil.
