Gravity and Dilution

[MSUCatBrewer]

Hi all,

I had a question regarding getting the proper FG and ABV.

I'm getting ready to brew my 3rd kit. First two are bottle conditioning. The FG on both came out lower than the kit "thought" it would...so the ABV was low.

In both cases I blindly followed the instructions and topped off at 5 gallons prior to pitching. Would it be better to top off slowly while resting the gravity until I hit the BG specified on the sheet, and then STOP topping off? Was my problem adding too much water post boil?

Thanks!

 

[LLBeanJ]

I would do a little math to figure out how much top off water is needed and add that amount.

Equation:
Current gravity points x current volume / expected gravity points = new volume

Example:
Pre top-off gravity = 1.065 (I.e., 65 gravity points)
Pre top-off volume = 3.75 gallons
Expected OG from recipe = 1.052 (I.e. 52 gravity points)

65 x 3.75 / 52 = 4.7 (rounded up) gallons
Add enough water to bring the total to ~4.7 gallons and you'll have an OG of 1.052

 

[McKnuckle]

Yes, now you are thinking beyond the rote directions, which shows you are digging in to the process more. It is perfectly acceptable to dilute less and correct a low OG. It's not "better" per se, but it's a valid choice.

I would just take care to get an accurate gravity reading first. Transfer your cooled wort to a fermenter, let it settle for an hour or so, then take a gravity reading. From there, use a dilution calculator to determine how much water to add, such as this one:

http://www.brewersfriend.com/dilution-and-boiloff-gravity-calculator/

[Edit - or use the math above]

I would not add water slowly and check gravity repeatedly - it's not necessary. The calculation will let you do it all in one shot, and should be "close enough for rock 'n' roll" as they say.

 

[MSUCatBrewer]

Great! Thanks for the feedback!

 

[RM-MN]

Hi all,

I had a question regarding getting the proper FG and ABV.

I'm getting ready to brew my 3rd kit. First two are bottle conditioning. The FG on both came out lower than the kit "thought" it would...so the ABV was low.

In both cases I blindly followed the instructions and topped off at 5 gallons prior to pitching. Would it be better to top off slowly while resting the gravity until I hit the BG specified on the sheet, and then STOP topping off? Was my problem adding too much water post boil?

Thanks!

You're thinking which is good but you are thinking backwards. Lower final gravity gets you a higher alcohol content, not lower. The formula which approximates the ABV is (OG-FG)x.131 (somebody correct this if it is wrong)

If you are reading the FG as alcohol you are on the wrong scale as that would indicate the "potential alcohol" or the sugars that could be fermented out if you were using simple sugars such as with a fruit juice that you were turning into wine.

 

[McKnuckle]

^Good catch... I assumed he meant OG (which I referenced in my reply), but he actually typed FG.

 

[LLBeanJ]

I also assumed (still do) that he meant OG, since he was talking about low ABV and topping off.

 

[flars]

Hi all,

I had a question regarding getting the proper FG and ABV.

I'm getting ready to brew my 3rd kit. First two are bottle conditioning. The FG on both came out lower than the kit "thought" it would...so the ABV was low.

In both cases I blindly followed the instructions and topped off at 5 gallons prior to pitching. Would it be better to top off slowly while resting the gravity until I hit the BG specified on the sheet, and then STOP topping off? Was my problem adding too much water post boil?

Thanks!

Were these all grain, all extract, or extract with steeping grains? Specific gravity can be thrown off if the wort is not thoroughly mixed. Your SG sample may come from part of the wort higher in sugars or part of the wort lower in sugars. Your samples will then error to a higher original gravity or error to a lower original gravity than indicated in the recipe.

 

[BlueHouseBrewhaus]

+1^ Extract kits are usually pretty much spot on as long as all your measurements were accurate. Almost every time, with extract kits suspect OG measurements are caused by inadequate mixing.

 

[MSUCatBrewer]

+1^ Extract kits are usually pretty much spot on as long as all your measurements were accurate. Almost every time, with extract kits suspect OG measurements are caused by inadequate mixing.

Both kits were extract, and like I said, they were my first two (done one day apart...I did this on the advice of a different board on the forum to do your first two ::bang bang:: and then go back and review your process with a critical eye...plus it got the "first time brew" yipps out of my system.

I'm thinking I didn't mix the wort prior to my test. Makes sense.

Should I take the OG reading BEFORE or AFTER I pitch the yeast? And if after, how soon after? And if before, should I take it after it has cooled to pitch temp?

Thanks!

 

[flars]

Both kits were extract, and like I said, they were my first two (done one day apart...I did this on the advice of a different board on the forum to do your first two ::bang bang:: and then go back and review your process with a critical eye...plus it got the "first time brew" yipps out of my system.

I'm thinking I didn't mix the wort prior to my test. Makes sense.

Should I take the OG reading BEFORE or AFTER I pitch the yeast? And if after, how soon after? And if before, should I take it after it has cooled to pitch temp?

Thanks!

I don't take OG readings any more with all extract kits if the kit is from a reputable source. The OG will be as stated in the recipe if all the extract is used and the volume in the fermentor is correct.

Factory volume markings on fermentors are often not accurate. It is best to pour a measured volume of water into fermentors to make your own gallon marks.

edit: An OG read would be best done after thoroughly aerating the wort for the best mixing possible.

 

[BlueHouseBrewhaus]

A great way to kill two birds with one stone is to shake the $#it out of your (sealed) fermenter after you top off and cool to pitching temp. This mixes and aerates your wort, both of which you should do before pitching. Once you've done this, take your OG measurement and pitch your yeast.