Low OG

[Mare_Mortis]

So today I transferred my first batch (Kolsch) into my secondary fermenter and brewed my second batch (IPA). I took an OG reading on the kolsch which should have been 1.040ish but it came out 1.030 (I expected as much since I ended up with a little over 5gal total) my reading on the kolsch today was 1.010. The IPA that I brewed today should have had a OG around 1.060 but it came out 1.048 and I made sure I was just shy of the 5 gal mark this time. Could it be that I am using soft water or is there something else that I am missing...

 

[boydster]

If you are extract brewing and hitting your volumes, you should be very close on your OG readings. Usually the issue is your top-off water not being thoroughly mixed. That is easily the most common reason to have a low OG with extract brewing. If you are doing all-grain, there are efficiency issues to address.

 

[Mare_Mortis]

Extract, Ill make sure to stir in my top off water next brew...if you need to bottle quietly, would stirring now help?

 

[Qhrumphf]

If you can accurately measure volume, you can take your gravity reading before you top off and then adjust for volume. Takes the top-off mixing issue out of the equation, since even with some heavy stirring you can't be sure of the accuracy. Because there's a finite amount of sugar present, the only thing changing when you top off is the density of the solution. Since that's more or less what specific gravity measures, it's simply a matter of conversion.

Use "gravity points" ie read 1.048 as 48, or 1.065 as 65, etc. etc. Then current gravity x current volume = new gravity x new volume. So 3 gallons of 1.084 wort means 3 x 84 = gravity x 5 (assuming 5 gallons), or 50.4. Meaning a gravity of 1.050 if you top off to 5 gallons.

It's the exact same math used for pre-boil gravity readings in all-grain brewing, and the same principle applies. Just a matter of either boiling off or adding back water.

Should also be noted that this equation only works if you accurately know the post-boil volume.

 

[boydster]

Extract, Ill make sure to stir in my top off water next brew...if you need to bottle quietly, would stirring now help?

Not sure what you want to accomplish here? If you need to bottle quietly, just don't make much noise. Or wait until the kids are already awake.

If you are talking about stirring the batch you just made to get the water to mix in, don't worry about that. If you have the right total volume, you have the right OG. Just because it might not be mixed thoroughly doesn't mean the sugar isn't there to ferment, it just means the sample you pulled wasn't an accurate representation of how much total sugar was in the wort. The yeast will handle business from here and mix everything for you while they eat the sugar.

 

[flatlanderHQ]

By the way you must aerate the wort vigorously prior to pitching your yeast. And plus one to calculating gravity / volume.

 

[sheldonsteen]

Extract, Ill make sure to stir in my top off water next brew...if you need to bottle quietly, would stirring now help?

I assume you mean bottle quickly? Don't stir after fermentation has begun. The good news is that once fermentation begins your top off water will get mixed in no problem on its own, but you may never know your actual OG. I use a wine degasser attached to my drill for about 5-10 mins to mix and properly aerate the wort before pitching. This is usually pretty effective for me.

 

[logan3825]

After pitching you want your beer to stay as still as possible. NO stiring, no sloshing if possible.

 

[hou_me]

I'm pretty new to all this, so my advice may not be worth much, but maybe you should check your hydrometer's accuracy. I noticed that mine always seemed a liitle high so I took a reading on plain old water (the same RO water that I brew with) and found that reading to pretty much match the difference between my expected OG and my actual OG. I wasn't off by that much so the whole exercise was mostly to satisfy my curiosity but if your hydrometer is off a little then maybe you're actually closer than you think.

-ben

 

[Hemphill]

I'm new to brewing as well so don't bash me please! that being said, is this formula correct since an additional two gallons of water would change the density of the wort?

 

[Demus]

Which formula do you mean?

 

[Hemphill]

The gravity/volume formula posted above using cross multiplication. He is stating you can predict your 5gal gravity reading by measuring your 3gal wort before top off. I was thinking the density would change the reading with the additional 2gallons of water. Or am I just over thinking this?

 

[Qhrumphf]

The gravity/volume formula posted above using cross multiplication. He is stating you can predict your 5gal gravity reading by measuring your 3gal wort before top off. I was thinking the density would change the reading with the additional 2gallons of water. Or am I just over thinking this?

You're right, it changes the density, and that's why it works. Specific gravity is based upon density (ratio of density of substance/wort vs. density of water). Adding equal volumes water to wort will cut the gravity in half, or whatever the ratio may be.

 

[Demus]

You're right, it changes the density, and that's why it works. Specific gravity is based upon density (ratio of density of substance/wort vs. density of water). Adding equal volumes water to wort will cut the gravity in half, or whatever the ratio may be.

++1

Think simple here. If you put a pound of sugar in a gallon of water, you'll get a certain density (gravity) fluid. If you now add 2 more gallons of water, you still have the same amount of sugar, it's just more dilluted (lower gravity).
The simple way this translates to beer is "gravity points". 3 gallons of say, 1.070 wort would be 210 gravity points (3 x 70). Now you can boil off water or add more but you'll still have 210 points. Lets say you add 2 gallons after your boil. Now you need to divide the same amount of points by 5. 210 divided by 5 is 42, or a 1.042 gravity. This is a mathematical certainty. The two most common errors though are uncalibrated hydrometers and unmixed top off water. Measuring your wort before topping off eliminates the second error. To eliminate the first check your hydrometer with distilled water at the calibration temperature and don't forget the temperature correction whenever your sample is a different temperature.
Hope this helps...

 

[Mare_Mortis]

++1
Hope this helps...

Very much so thanks

 

[Hemphill]

Got it! Thanks so much. I've definitely forgot to stir or not stirred my top off well enough due to haste. This definitely removes room for error!

 

[speeddemon190]

This helped me as well, I had a low OG reading. extract off by 14 points (1st time its happened in my 10 or so brews) and I now realize i didnt stir my top of water...so maybe my gravity was ok. Thanks again everyone for the help!!

 

[Qhrumphf]

Just going to put this out there, I'm all for taking measurements, but taking an OG reading with an extract batch isn't really all that necessary. If you add the right amount/kind of fermentables, and you have the correct batch volume, your gravity is going to be correct, and you can assume that the gravity your recipe (or software) provided is accurate. If you're using a different maltster for your extract (there's some slight variation, one brand of DME may provide 40 ppg of fermentables, where another may provide 44 ppg) it might change a tiny bit, but insignificantly.