OG Measurement Question

[mplsbrewer]

Hello,

I have a question regarding OG measurements. I just boiled an IPA recipe which, according to my calculations, should yield an OG of 1.071. My actual hydrometer measurement came out to 1.090 (twice). Wort temperature was ~75F, so temp correction should be pretty small. My question is, does sediment in the sample (hops/coagulated protein trub) affect the measurement? I didn't pull a particularly clean sample either time, but I wouldn't think it would affect OG since these are suspended particulates and not actually dissolved in the wort. Or are my calculations way off? I'm not using any brewing software, just an Excel calculator I created.

Here's the recipe:

1 lb 40L Crystal (steeped 30 min at 155F)
.25 lb Biscuit malt (steeped 30 min at 155F)

6 lb Pilsen light extract
3.3 lb Amber ale extract

1 oz Columbia - 60 min
0.5 oz Centennial - 30 min
0.5 oz Centennial - 10 min
1 oz Cascade - 2 min

Thanks!

 

[TipsyDragon]

well there are a few possibilities here. this sediment as you call it only displaces the liquid it doesn't actually change its density which is what they hydrometer is measuring.

the most likely explanation is you drew your sample from the bottom of the pot. extracts tend to sink to the bottom and if you drew your sample from there you will get a false high reading.

another possibility is you didn't top off to your target starting volume before taking your reading. if the batch size is 5.5 and you have only 5 or less gallons of beer in your pot you will also get a false high reading.

 

[Revvy]

one thing to realize is the it is hard to miss your OG in an extract batch, and in reality you more than likely DIDN'T.....It's just that it is USUALLY difficult for the original gravity to actually REFLECT this fact.

It's a pretty common issue for ANYONE topping off with water in the fermenter (and that includes partial mashes, extract or all grain revcipes) to have an error in reading the OG...In fact, it is actually nearly impossible to mix the wort and the top off water in a way to get an accurate OG reading...

Brewers get a low reading if they get more of the top off water than the wort, conversely they get a higher number if they grabbed more of the extract than the top off water in their sample.

When I am doing an extract with grain recipe I make sure to stir for a minimum of 5 minutes (whipping up a froth to aerate as well) before I draw a grav sample and pitch my yeast....It really is an effort to integrate the wort with the top off water...This is a fairly common new brewer issue we get on here...unless you under or over topped off or the final volume for the kit was 5 gallons and you topped off to 5.5, then the issue, sorry to say, is "operator error"

If your target volume was correct, then it will be fine.

More than likely your true OG is really what it's supposed to be. And it will mix itself fine during fermentation.

 

[mplsbrewer]

I did draw the sample from the bottom of the fermenter after transferring the wort and topping off to 5 gallons. I'm guessing the top off water was not homogeneously mixed when I sampled. Thanks for the feedback!

 

[Calder]

1 lb 40L Crystal (steeped 30 min at 155F)
.25 lb Biscuit malt (steeped 30 min at 155F)

6 lb Pilsen light extract
3.3 lb Amber ale extract

1 oz Columbia - 60 min
0.5 oz Centennial - 30 min
0.5 oz Centennial - 10 min
1 oz Cascade - 2 min

Thanks!

You didn't say if the extract was DME or LME. I'm assuming the Pilsen is DME and the amber is LME.

My calculation for OG in 5 gallons:

Crystal = 15 points
Pilsen = 46x6 = 276
Amber = 36x3.3 = 119

Total points = 410

In 5 gallons = 1.081

 

[mplsbrewer]

The Pilsen Light and Amber were both LME, so I assumed 37 points for each of them, which is where my calculation differs from yours, Calder (we're pretty much the same for the steeping grain value).

Pilsen LME: 6 lb x 37 ppg = 222 points
Amber LME: 3.3 lb x 37 ppg = 122 points
Biscuit Malt: 0.25 lb x 36 ppg x 0.3 assumed steeping efficiency = 3 points
Crystal 40L Malt: 1 lb x 34 ppg x 0.3 assumed steeping efficiency = 10 points

357 points total; theoretical OG = 1.071


I looked on the Briess website for points data. The .pdf data sheets for each extract did have a table correlating how many lbs/gal of extract to use to reach a desired OG, but nothing explicitly stating the points value. I was too lazy to calculate that, so just assumed 37. Is that a reasonable assumption, or is there a good resource that lists specific extract points values, such as what you used?

 

[Cornraker]

It's a pretty common issue for ANYONE topping off with water in the fermenter (and that includes partial mashes, extract or all grain revcipes) to have an error in reading the OG...In fact, it is actually nearly impossible to mix the wort and the top off water in a way to get an accurate OG reading...
.

This answered the question i was wondering. I measured 1.046 when it should have been 1.052. Makes sense.