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Old 02-25-2010, 04:08 PM   #1
Dunkelweizenpants
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Default Can tons of hops affect your gravity reading?

Hi guys,

Been brewing extract for about 2 years and have a question about taking gravity readings. I recently brewed a very hoppy amber ale which included adding 1.5oz of hops at knockout. Transferred to primary and took a reading that was MUCH higher than I had calculated (I was shooting for 1.072 and hit 1.086). There were plenty of hops in suspension in the hydrometer tube.

Fast forward 5 days, fermentation is still pretty active and I took a sample (I use Better Bottle with a spigot) and there were still plenty of hops in suspension in the hydrometer tube. Gravity read 1.030.

I left this sample with hydrometer in place sitting out overnight. A sediment formed in the bottom of the hydrometer tube and my hydrometer now read 1.026.

Question - did the gravity drop .004 points because the hops in suspension had settled out, or due to something else? Wondering now what my true OG reading was...

Thanks!

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Old 02-25-2010, 04:23 PM   #2
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I would guess that the .004 drop you saw was from fermentation that was still taking place. There were probably still a ton of yeasties in your sample and overnight was plenty of time for them to ferment down a bit.

I have not noticed that hops affect my gravity readings. The hydrometer measures the dissolved sugar and I cant imagine that the hops would affect the sugar content

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Old 02-25-2010, 04:28 PM   #3
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If hops stick to the hydrometer it will throw off the readings from a minor correction to a major deal. If not then it has no effect. Same thing with bits of grain or any other particles. Overnight temperature changes would have an effect on gravity readings as well as bubbles or foam on the side of the hydro in addition to continued fermentation in such a small vessel.

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Old 02-25-2010, 11:44 PM   #4
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Quote:
Originally Posted by chode720 View Post
The hydrometer measures the dissolved sugar and I cant imagine that the hops would affect the sugar content
Technically, this is not true. The hydrometer measures the specific gravity of a liquid. A high gravity wort is high in sugar, and the sugar is what causes the the SG to be above 1.0 (SG of plain water), however the hydrometer is not measuring the sugar content itself.
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Old 02-25-2010, 11:50 PM   #5
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Quote:
Originally Posted by Dunkelweizenpants View Post
Question - did the gravity drop .004 points because the hops in suspension had settled out, or due to something else?
hops chunks wont affect a SG reading. all they do is displace liquid not change its density. its posable the difference was due to a temperature change or continued fermentation in your sample.
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Old 02-26-2010, 12:04 AM   #6
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Quote:
Originally Posted by firebird77 View Post
Technically, this is not true. The hydrometer measures the specific gravity of a liquid. A high gravity wort is high in sugar, and the sugar is what causes the the SG to be above 1.0 (SG of plain water), however the hydrometer is not measuring the sugar content itself.
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hops chunks wont affect a SG reading. all they do is displace liquid not change its density. its posable the difference was due to a temperature change or continued fermentation in your sample.
Exactly because the main difference is this: the hops aren't dissolved within the liquid however the sugar is.
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Old 02-26-2010, 12:08 AM   #7
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Quote:
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Exactly because the main difference is this: the hops aren't dissolved within the liquid however the sugar is.
I'm pretty sure that the acids from the hops do dissolve in the wort, and the gravity of acids can be pretty high, but I don't know how much acid you would have to have for noticeable change in gravity.
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Old 02-26-2010, 01:41 PM   #8
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IBU = mg/L (AKA ppm), so the dissolved alpha acids won't make any difference.

I've occasionally had trouble with floaties and my precision hydrometer, as there is very little clearance between the bulb and the tube. Not a problem with the regular one.

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Old 02-26-2010, 01:46 PM   #9
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Is it possible that the temperature of the sample changed after leaving it out on the counter all night, and that is why it might have dropped the 0.004?

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Old 02-26-2010, 01:55 PM   #10
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Quote:
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Is it possible that the temperature of the sample changed after leaving it out on the counter all night, and that is why it might have dropped the 0.004?
That's a pretty big temp swing to cause that much, but it is a very good observation to bring up.

Scott
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