Efficiency, Original Gravity, and Final Gravity

Hi!

I just finished using BeerSmith for the fourth time and am generally very happy with the results.  However, I've noticed that my measured original gravity and final gravity are consistently .005 to .015 lower than the values the program estimated.  My ABV almost always works out as planned (assuming an efficiency of roughly 70%), but my most recent batch has me worried.

I did a weizenbock where I aimed for an original gravity of 1.085, but my measured original gravity ended up 1.060.  I know I'm not going to end up with my planned ABV, as it would take a final gravity of .9957, but I'm having trouble believing that my efficiency dropped very much compared to prior batches.

I usually do a single step infusion with an infusion mash-out, but for the weizenbock I did a triple decoction mash in addition to a decoction mash-out.  I hit all the planned temperatures more or less spot-on.  My mash/lauter tun is a 10 gallon cooler with a false bottom, and I batch sparged with the minimal amount of sparge water involved in my recipe.

Any idea about what's going on with the lower values?  Is it possible that my hydrometer is just off?  Am I missing something obvious?  I spent a good bit of time searching for answers on this and other forums and websites, so I hope I haven't missed another post on the same topic.

Anyway, I've enjoyed perusing the forum for a while now, and I look forward to becoming part of the community here.  Thanks!


Matt

Hi,
  What number are you using for brewhouse efficiency?  This number drives the OG estimate, so it may be possible you are using too large a number and just need to adjust it down a few percent.

  Also, measuring volume is important - as that can significantly sway your readings.

  To get an idea of how you are actually doing you can click on the "Brewhouse Efficiency" button in the recipe you brewed and enter your actual volumes and OG's -- BeerSmith will calculate your actual efficiency from that and you can use that number to better adjust your next batch.

Thanks,
Brad

Higher gravity beers tend affect efficiency, you should really expect to get lower efficiency when you produce a bigger beer.

I have not really made many brews using a decoction mash so I could be just shooting in the dark here, is it possible that 4 decoctions denatured a lot of the enzymes and perhaps conversion was hampered by this?
Perhaps the Sacch rest needed to be extended to allow the remaining enzymes to complete the conversion.

Cheers
Andrew

Thanks for the responses!  I usually estimate my brewhouse efficiency to be 70%, but I did take into account the high gravity of the batch this time and was only hoping to get 65% brewhouse efficiency.  What's frustrating is that with an OG of 1.060, I'm looking at 46% actual efficiency.

The weird thing is that so far I've always ended up with the ABV for 70% or better brewhouse efficiency when my actual efficiency is only around 60%.  For instance, several weeks ago I followed the Wit recipe that came with the program (awesome recipe, by the way...thanks!), and I ended up with a measured OG of 1.037 and a measured FG of 1.001.  ABV was right on target for 75% brewhouse efficiency,  but my actual efficiency was 59%.  Any idea what caused the problem?

My concern is that if I start hitting my estimated OG exactly, I'll end up with way-too-alcoholic beers.  Right now, the beers taste pretty much as planned, with the intended color and ABV too, but my gravities are way off.  Not a huge problem in my opinion, but I'm still a little confused by the discrepancy in numbers.

Which volume measurement do you mean?

Matt,

Sounds like your hydrometer is out of calibration. Have you tested it in distilled water to see if it reads correctly (0.000) ?
The same could apply for a Refractometer if you use one.
A low O.G and a corresponding low F.G could mean a faulty hydrometer reading.
A low O.G should not necessarily mean an extremely low F.G unless you used a lot of sugar or mashed very low. Your attenuation is obviously good so I would think your problem is related to faulty equipement.

Andrew

I haven't tried it with distilled water, but when I put my hydrometer in Chandler, AZ tap water, the bottom of the meniscus is at 1.000 and the top is at .990.  I'm used to reading from the bottom of the meniscus, but I just looked at the instructions that came with my hydrometer, and there's a diagram with an eye looking at a line at the top of the meniscus.  The caption says "reading upper meniscus."  I'm not sure of the brand of the hydrometer, but it says "Wine & Beer hydrometer" and is made in France.  If I do indeed have to read from the top of the meniscus, I guess my problem is solved.  Pays to read the instructions!

Andrewqld said:

I have not really made many brews using a decoction mash so I could be just shooting in the dark here, is it possible that 4 decoctions denatured a lot of the enzymes and perhaps conversion was hampered by this?
Perhaps the Sacch rest needed to be extended to allow the remaining enzymes to complete the conversion.

Cheers
Andrew

Click to expand...

This should not be a problem with a decoction,  there should be plenty of enzymes left for conversion.  An effect of decoctions is to boost efficiency, 5% is not unusual.  The boiling action really breaks down the grains making everything extremely available.  Just make sure you have a sufficient rest after adding the decoction back in.

When decocting for mashout pull just the liquid, no grains.

Fred

I've never done decoction, however I recently raised my efficiency from 60-65% to over 80% simply by raising my mash temp and using a hotter sparge.
Sugar dissolves more the warmer the water, of course if you get things too hot you'll get tannins which while being desireable in wine are not a good thing to have in beer.

I think we have the same hydrometer. Did you notice that it is calibrated for 600F? A higher temperature will give you a lower specific gravity. A lower temperature shows a higher gravity. Since you seem to get consistent ABV (a function of OG-FG) but equally consistent low gravities, perhaps you are reading at too high a temperature?

Just a thought.

- Hare

...perhaps you are reading at too high a temperature?

Funny you mention that.  I made a batch over the weekend, a low octane 'red' intended for a friend's bbq this July.
The intent was a S.G. in the 1.035-1.040 range, low alcohol so as to not result in a bunch of OUIs on a Saturday afternoon.
I tasted the wort before the boil and it was decidedly weak, so I put some into the hydrometer.  It read 1.022 so I freaked out, thinking I'd miss-weighed my grain I added 1# each LME and DME at the end of the boil, the goal being to raise the S.G. by .016 or so.
Then I remembered temperature and consulted the chart that said at 118 degrees you should add .01 to your reading, so at 150 degrees my 1.022 was probably right around my intended target.  The reading before pitching my yeast of 1.050 only confirmed this.

Lesson learned - temperature matters when measuring specific gravity.

Maine Homebrewer said:

I made a batch over the weekend, a low octane 'red' intended for a friend's bbq this July.

The intent was a S.G. in the 1.035-1.040 range, low alcohol so as to not result in a bunch of OUIs on a Saturday afternoon.

Click to expand...

Remind me to avoid your BBQ's.

Maine Homebrewer said:

I tasted the wort before the boil and it was decidedly weak, so I put some into the hydrometer.  It read 1.022 so I freaked out, thinking I'd miss-weighed my grain I added 1# each LME and DME at the end of the boil, the goal being to raise the S.G. by .016 or so.

Click to expand...

I brewed extract for years. I always boiled that stuff for a full 60 mins. Why did you add it at the end?

Maine Homebrewer said:

Then I remembered temperature and consulted the chart that said at 118 degrees you should add .01 to your reading, so at 150 degrees my 1.022 was probably right around my intended target.  The reading before pitching my yeast of 1.050 only confirmed this.

Click to expand...

Where did you get that chart? I haven't looked but I bet Beer Smith does that conversion. (Note to self: Check the OG tool...)
I waste a lot of time cooling wort to 60F to take gravity.

- Hare

My hydrometer came with a temperature correction in the instruction sheet.

At 70° add 1
at 77° add 2
at 84° add 3
at 95° add 5
at 105° add 7

Example
Temperature is 84 degrees F
Specific gravity reads 1.035
Correction figure is 3
Corrected gravity is 1.038

Hi,
  Actually the hydrometer correction can be done with the hydrometer tool in BeerSmith - just enter the temperature of your reading and the reading itself.

Cheers,
Brad

what Bilbo said