Gravity Readings

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Dlax006

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As a new brewer, I've done about two brews, but never really paid attention to gravity readings. I've just been trying to get the bare-bones of the process down to this point. Now, I'm ready to get more technical, and get better brewing results. My question is, at what point during the brewing process do I take an original gravity reading and final gravity reading? Are there other points during the process I should be taking readings also? Any advice is much appreciated! Thank you!
 
You take the OG reading after thoroughly mixing wort & top off water & aerating. But before pitching yeast. Then wait till the 2 week mark,& test again to see how close to FG you are. Some even wait 3 weeks to take an FG reading. When the numbers are the same 2 days apart,it's ready to package.
 
In all honesty, taking gravity readings should have been apart of your initial process. But to answer your question, you can take an OG reading after your boil process and when it's cooled. You'll want to take it before pitching the yeast. For FG you'll want to wait a few weeks after pitching the yeast, take a reading between 14 and 21 days, wait two to three days and take another. If it remains constant, the beer is done.
 
I try to take readings as close to the temp my hydrometer is calibrated to as possible (60f). I am around that point after adding cold water to my cooled boil, so I take it then, right after pitching yeast. I mostly have been trying to hold that temperature for fermenting, so I take another reading when I think it is getting close to done fermenting or completely done. Then I check again after a few days to ensure it is stable and then bottle.

Feel free to check more to see how fermentation is progressing, but I don't think any more are necessary.

And it isn't a problem to check at temperatures other than where your hydrometer is calibrated, you just have to make an adjustment to your reading based on the temperature.
 
unionrdr said:
You take the OG reading after thoroughly mixing wort & top off water & aerating. But before pitching yeast. Then wait till the 2 week mark,& test again to see how close to FG you are. Some even wait 3 weeks to take an FG reading. When the numbers are the same 2 days apart,it's ready to package.

Before pitching? Oops...

Is there a reason for that? Learn something new every day...
 
Well,the yeast would ad to the gravity I think. It's also a good practice to do it before pitching,as most will pitch & seal it up straight away. Then remember later that they didn't take an OG reading.
 
Good call. I guess I figured that since the yeast will be in for final gravity measurements, I should do OG measurements with it present as well.

As far as practical measurements go, how critical is it to do it one way or the other? The only thing it will affect is the calculation of ABV, correct? Anyone have an idea how far off the ABV calc will be?

As long as one is consistent batch to batch, is it something to worry about?
 
I take a sample right before pitching yeast. Then I take a sample after about a week. Then another a day before bottling. This way I can compare the gravities after about a week (which for most beers is enough time to fully ferment) and after it's cleaned up. Knowing they are they same assures that the fermentation is complete and that you won't get bottle bombs!

Good call. I guess I figured that since the yeast will be in for final gravity measurements, I should do OG measurements with it present as well.

As far as practical measurements go, how critical is it to do it one way or the other? The only thing it will affect is the calculation of ABV, correct? Anyone have an idea how far off the ABV calc will be?

As long as one is consistent batch to batch, is it something to worry about?

The ABV part of the scale should be ignored for beer purposes. But, if you did make note of where this was before your beer started fermenting, take out your hydrometer and look at the specific gravity that corresponds to that same level of "ABV." That would be your OG.
 
It's just excepted practice to get a more accurate OG reading before the pitch. Later on,while it is present,there's less sugar,having been converted to alcohol. Alcohol is lighter than the sugars,so the specific gravity reads lighter.
 
Thanks.

I guess what I am trying to ask is this. Since I use my hydrometer primarily to ensure I have a steady FG, pre- or post-pitch doesn't matter, correct?

Where it does matter is in the CALCULATION of ABV (based on OG-FG), correct? (JordanThomas, I think you misunderstood because I am only reading gravitates, not ABV directly.)

I guess what I am really wondering is how do I get the most accurate numbers for my ABV calculation? What complicates this is that the amount of yeast in suspension changes as the beer ferments.

Maybe I should ask this: when fermentation is complete, how much yeast is in suspension and how does this compare to the values of yeast in suspension pre- and post-pitch (ie. 250M cells and end of fermentation is closer to zero than to 1B cells at pitch, so pre-pitch is more accurate)? Have I taken this too far? Thanks again, everybody. Sorry if I have hijacked the thread.
 
Thanks.

I guess what I am trying to ask is this. Since I use my hydrometer primarily to ensure I have a steady FG, pre- or post-pitch doesn't matter, correct?

Where it does matter is in the CALCULATION of ABV (based on OG-FG), correct? (JordanThomas, I think you misunderstood because I am only reading gravitates, not ABV directly.)

I guess what I am really wondering is how do I get the most accurate numbers for my ABV calculation? What complicates this is that the amount of yeast in suspension changes as the beer ferments.

Maybe I should ask this: when fermentation is complete, how much yeast is in suspension and how does this compare to the values of yeast in suspension pre- and post-pitch (ie. 250M cells and end of fermentation is closer to zero than to 1B cells at pitch, so pre-pitch is more accurate)? Have I taken this too far? Thanks again, everybody. Sorry if I have hijacked the thread.

I think you are over-thinking it. I'm pretty sure the yeast adds nothing to the gravity. You can take an OG after you pitch, but as was said, it's more habit to close up right after pitching and you forget to take a reading. The number of yeast in suspension is inconsequential, the gravity reading is based on sugar content. Wort is high in sugars and is "heavier", beer is lower in sugars after the yeast get to it and is "lighter". The best way to make sure your ABV is accurate is to take accurate hydro readings and make sure your hydrometer is calibrated properly. There are ABV calculators online to help you do the math, but the input numbers have to be right.
 
Thanks.

I guess what I am trying to ask is this. Since I use my hydrometer primarily to ensure I have a steady FG, pre- or post-pitch doesn't matter, correct?

Where it does matter is in the CALCULATION of ABV (based on OG-FG), correct? (JordanThomas, I think you misunderstood because I am only reading gravitates, not ABV directly.)

I guess what I am really wondering is how do I get the most accurate numbers for my ABV calculation? What complicates this is that the amount of yeast in suspension changes as the beer ferments.

Maybe I should ask this: when fermentation is complete, how much yeast is in suspension and how does this compare to the values of yeast in suspension pre- and post-pitch (ie. 250M cells and end of fermentation is closer to zero than to 1B cells at pitch, so pre-pitch is more accurate)? Have I taken this too far? Thanks again, everybody. Sorry if I have hijacked the thread.

Yes, I must have misunderstood. The yeast in suspension is needed at the end of your beer in order to carbonate it in the bottle. To have the most accurate ABV calculation, you just want to make sure that you have a properly working hydrometer, ensure that any residual carbonation bubbles have been removed (I just use a rolled up piece of paper towel dipped into my test tube) and that the sample is at 59-60F. Then make sure you measure at the cusp of where the liquid meets the glass of your hydrometer. There's a term for that cusp, but I cannot recall. If you are off by 1 point, it would only amount to about .1% difference, so don't sweat it too much.
 
Take OG before pitch. You dont want to waste the new yeast that will stick to the sides of your thief and ends up in your test tube. that sample you should drink rather than return to the fermenter.
 
Yes, I must have misunderstood. The yeast in suspension is needed at the end of your beer in order to carbonate it in the bottle. To have the most accurate ABV calculation, you just want to make sure that you have a properly working hydrometer, ensure that any residual carbonation bubbles have been removed (I just use a rolled up piece of paper towel dipped into my test tube) and that the sample is at 59-60F. Then make sure you measure at the cusp of where the liquid meets the glass of your hydrometer. There's a term for that cusp, but I cannot recall. If you are off by 1 point, it would only amount to about .1% difference, so don't sweat it too much.

I believe you are looking for "meniscus" :fro: :mug:
 
Only dissolved compounds affect the gravity. Anything in suspension, like yeast, will have no affect. There is no necessary reason to take an OG reading before pitching the yeast - there should be plenty in there so that you don't need to worry about removing some (if you pitch so little yeast that this is a concern, you've got bigger concerns than that). Like others have already mentioned, taking a reading before pitching is the norm. But if you forget and need to take a reading after you pitch, you'll be fine. Assuming of course you remember soon after pitching, before the yeast have started working on the sugars.
 
JLem said:
Only dissolved compounds affect the gravity. Anything in suspension, like yeast, will have no affect...

I wondered about this, but wasn't sure so I didn't mention it. Yeast (although small and individually invisible in a liquid) is an undissolved solid which shouldn't have an effect. Thanks!
 
They are both alcohol indicators and neither is more right than the other. I think it depends on where you are as far as the value you are used to. I always read ABV, so that is what I am used to. Because alcohol is less dense than water, ABV will always be higher than ABW. Both can be calculated from the difference in OG and FG. For instance if OG is 1.059 and FG is 1.010, ABW is 5.2% and ABV is 6.6%.

Somebody check my math.
 
Hi, i just want to know what is the difference between alcool by volume and alcool by weight? Wich one is the alcool indicator?

Thanx

ABV is the typical alcohol content indicator. Because you are drinking 12 ounces... It's the same amount of alcohol regardless, but different beers would have different weights, so if you wanted to think about it that way you would use ABW.

Never saw anyone measure by weight though. That just seems strange...
 
Thanks for all the input! The more educated I am, the better beer I'll produce (and enjoy). I'm sure you all will be getting more than a few more questions from me in the future! I'm already beginning to become intrigued with partial mashing. Anyway, thanks again everyone! :mug:
 
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