Pressurised fermentation and absorbed Co2 affecting FG reading?

[Frisp]

I have pressure fermented a cheap lager kit for a week and today took a hydrometer. when I pulled a sample from the fermenter it had a stunning head on it and well carbonated. so i juggled it between jugs tp remove as much Co2 as I could from the sample, and got 1.012 at 21C

However Im sure there must still be C02 in suspension will that Co2 skew the hydrometer reading. ? or wont it ?

 

[RoomWithABrew]

I think it skews it if bubbles accumulate on your hydrometer.

 

[Agentgonzo]

Dissolved CO2 doesn't affect the SG of the wort/beer in any meaningful way. As mentioned, it's only the bubbles clinging to the hydrometer that will affect it, so just give your hydrometer a spin and it'll dislodge all the bubbles.

 

[foxy]

I have pressure fermented a cheap lager kit for a week and today took a hydrometer. when I pulled a sample from the fermenter it had a stunning head on it and well carbonated. so i juggled it between jugs tp remove as much Co2 as I could from the sample, and got 1.012 at 21C

However Im sure there must still be C02 in suspension will that Co2 skew the hydrometer reading. ? or wont it ?

Carbonated beer will certainly throw off your FG reading, degas the finished beer which you seem to have done.


https://byo.com/article/hydrometers-and-refractometers/

 

[Frisp]

Carbonated beer will certainly throw off your FG reading, degas the finished beer which you seem to have done.


https://byo.com/article/hydrometers-and-refractometers/

thanks a worthwhile wee read

 

[peebee]

thanks a worthwhile wee read

You think? But you are assuming the writer knows what he's talking about.

I'm often ridiculed for the instrument I use, but at least I don't have to describe it with untruths and down-right fibs. So, because I'm ridiculed, I'm going to tear this awful article to pieces ...

First untruth ... "Hydrometers use density to measure the dissolved solids ...". No they don't, they use buoyancy. Density is mass divided by volume. To use a hydrometer, you neither weigh the specimen nor measure its volume.

Next untruth, or in this case deceit (fib, white lie, whatever you'd like to call it). And it's the one key to this query: "Hydrometer readings can also be skewed with carbon dioxide dissolved in solution. Whether the beer has just finished fermentation or the beer has been carbonated, carbon dioxide is going to lift the hydrometer up in the cylinder and give a false reading. ...". Read it carefully. It actually is saying that bubbles forming on the hydrometer are skewing the reading just like the guys here have been telling you. But it's written to give the impression dissolved CO2 is what's skewing the measurement. Smoke and Mirrors, for what gain I don't know. Carbon Dioxide bubbles create buoyancy, hydrometers measure buoyancy. If I was @foxy I'd be pretty peeved being drawn into that deceit.

Enough! I could go on, but I think two blatant, key, errors are enough to discredit that article.

 

[foxy]

You think? But you are assuming the writer knows what he's talking about.

I'm often ridiculed for the instrument I use, but at least I don't have to describe it with untruths and down-right fibs. So, because I'm ridiculed, I'm going to tear this awful article to pieces ...

First untruth ... "Hydrometers use density to measure the dissolved solids ...". No they don't, they use buoyancy. Density is mass divided by volume. To use a hydrometer, you neither weigh the specimen nor measure its volume.

Next untruth, or in this case deceit (fib, white lie, whatever you'd like to call it). And it's the one key to this query: "Hydrometer readings can also be skewed with carbon dioxide dissolved in solution. Whether the beer has just finished fermentation or the beer has been carbonated, carbon dioxide is going to lift the hydrometer up in the cylinder and give a false reading. ...". Read it carefully. It actually is saying that bubbles forming on the hydrometer are skewing the reading just like the guys here have been telling you. But it's written to give the impression dissolved CO2 is what's skewing the measurement. Smoke and Mirrors, for what gain I don't know. Carbon Dioxide bubbles create buoyancy, hydrometers measure buoyancy. If I was @foxy I'd be pretty peeved being drawn into that deceit.

Enough! I could go on, but I think two blatant, key, errors are enough to discredit that article.

I think he knows a lot more than most about brewing, after getting his BA in biology at Colby College he has been working in the brewing industry and now writes a lot of knowledgeable articles for BYO.
I always de-gas that way my bases are covered.

 

[Frisp]

I think he knows a lot more than most about brewing, after getting his BA in biology at Colby College he has been working in the brewing industry and now writes a lot of knowledgeable articles for BYO.
I always de-gas that way my bases are covered.

I think Ill cover my bases too.
Next ferment is going to have an i spindle charting its progress and all I want from that is to indicate that fermentation has flatlined, I shant be using any gravity readings from it . As for ABV I shall get my OG by refractometer and FG from a Hydrometer reading in a degassed sample .

 

[Agentgonzo]

As for ABV I shall get my OG by refractometer and FG from a Hydrometer reading in a degassed sample .

Measure the OG with a hydrometer as well. Google "wort correction factor" because Refractometers are calibrated for the wine industry so measure fructose not maltose. Refractometers can vary (just like any other piece of equipment), especially cheap ones from eBay /Amazon (my wort correction factor is 0.9, not 1.04). Of course, if the two differ, you won't know which one is actually correct

As explained by Peebee, you don't need to go crazy with degassing it - as long as there aren't any bubbles clinging to the hydrometer you'll be fine (ie what you've already done). Full degassing won't hurt though, but won't achieve anything. If you want to prove it to yourself degas sufficiently to get rid of bubbles, give the hydrometer a spin to knock off any remaining bubbles and take a reading. Then thoroughly degas and wait 24 hours to be sure there's no CO2 in solution and measure again. You'll notice the reading is the same. (Or if you have a soda stream you can measure your tap water, carbonate it a bit and measure again ensuring no bubbles cling to the hydrometer).

 

[hoppyscotty]

Measure the OG with a hydrometer as well. Google "wort correction factor" because Refractometers are calibrated for the wine industry so measure fructose not maltose. Refractometers can vary (just like any other piece of equipment), especially cheap ones from eBay /Amazon (my wort correction factor is 0.9, not 1.04). Of course, if the two differ, you won't know which one is actually correct

As explained by Peebee, you don't need to go crazy with degassing it - as long as there aren't any bubbles clinging to the hydrometer you'll be fine (ie what you've already done). Full degassing won't hurt though, but won't achieve anything. If you want to prove it to yourself degas sufficiently to get rid of bubbles, give the hydrometer a spin to knock off any remaining bubbles and take a reading. Then thoroughly degas and wait 24 hours to be sure there's no CO2 in solution and measure again. You'll notice the reading is the same. (Or if you have a soda stream you can measure your tap water, carbonate it a bit and measure again ensuring no bubbles cling to the hydrometer).

Yep...


I usually leave my samples out for a good while to get to the right temp before measuring and if it's carbonated give it a good stir to Degas. Degassing doesn't take long. Just think how quickly a glass of beer or Coca Cola goes flat if you leave it out.

 

[Agentgonzo]

Enough! I could go on, but I think two blatant, key, errors are enough to discredit that article.

I wouldn't necessarily agree with saying they are errors and it discredits the article. The author has tried to simplify the physics to make it easier to be understood by beginners and those who don't have a good grasp on the science - which is a good aim for an introductory article like the above.

As with all simplifications (over simplifications?) It causes confusion when people assume it is 100% true and correct (which it isn't, and wasn't intended to be). It is then made worse by people in the internet echo chamber repeating their misunderstanding and quoting it as definitive source of truth, which leads to more beginners misunderstanding the science and the situation perpetuates itself. It takes people like Peebee to point out the inaccuracies in the simplification (I'm sure if you contacted the author, they would be the first to agree it's a simplification and peebee's analysis is accurate), but not everyone will have read it and the misunderstanding continues to be perpetuated.

 

[peebee]

I think he knows a lot more than most about brewing, after getting his BA in biology at Colby College ...

WHAT! That makes it many times worse! He knows his stuff (or should) yet writes drivel! Although to be fair, Biology won't necessarily help him discussing topics of Physics.

I'd have far more sympathy if he was an ordinary homebrewer who has picked up some dodgy information.

Note: I am in no-way criticising you for falling foul of this rubbish. But I might if you keep supporting it! Which might not go down well with the others if I settle into a lengthy dialog discussing the other points of nonsense in that article. During which I might even mention pyknom... mmm...mmph ...

 

[peebee]

I wouldn't necessarily agree with saying they are errors and it discredits the article. ...

Mmmm-gumph, Perhaps. But he still said "Hydrometers use density ..." when they don't. An inexcusable error in my book. Hydrometers use buoyancy, which is slaved to density and hydrometers are graduated in a density scale. And not an ordinary density scale, but one that's "relative" to water (relative density or specific gravity). Hence water is SG 1.000, not because water's density is close to 1.000g/ml at 4°C, that's just a by-the-way (ask an American who doesn't measure things in "metric").

Okay, that's a long-winded explanation, but "Hydrometers use density ..." isn't simplifying, it's confusingly wrong. I'm particularly sensitive to it because I was making this wrong assumption for years before figuring it out.

 

[Agentgonzo]

Hydrometers use buoyancy, which is directly related to density. Is that a simplification, or an error - I suppose that's in the eye of the beholder.

Given people have already got the science wrong from his simplification/error, I have a feeling they would have got the science even more wrong if he'd introduced buoyancy

 

[peebee]

... I have a feeling they would have got the science even more wrong if he'd introduced buoyancy

Certainly. Buoyancy is horribly convoluted. But perpetuating the idea that the hydrometer is the tool to measure "gravity" when gravity isn't even a native thing for a hydrometer to measure is a deceit. Perhaps okay when typical weighing scales weren't up to the job, but these days weighing scales at a reasonable price are up to the job. Because hydrometers can't weigh and can't measure volumes, (they measure buoyancy remember) they have to be "calibrated" to a particular temperature ... which homebrewers ignore, and instead worry the scale isn't precisely zeroed, etc.

Less deceit will help users to use hydrometers correctly, or else understand when they are not using them in the most optimum manner.

There isn't really any excuse for using deceit.

 

[foxy]