Final Og Lower Than Og Into Boiler

[NeilArge]

Put down an APA yesterday (a SNPA clone adapted from the Northern Brewer forums). Everything went okay, and I was pretty stoked to get 26 litres of wort at 1.056 into the boiler. I put the sample into the fridge to get it down to 20C before reading. Imagine my surprise when I took the final OG out of the fermenter last night and it read 1.052. Any clues as to what has happened here? I did a 70 minute boil and lost 3 litres along the way through boil-off.

Yours

Perplexed

 

[raven19]

Error in the reading maybe?

Sounds impossible if you corrected the temp of the wort.

Perplexed +1 !!!

 

[apd]

g'day ToG,

When you put the sample in the fridge, was it covered? If it was in the fridge, uncovered for a while, some of the liquid might have evaporated which would give you a high gravity reading.

Also, if you haven't pitched your yeast yet, perhaps you have an infection that has started to chew through the wort.

Out of interest, why were you taking two OG readings?

Andrew

 

[NeilArge]

g'day ToG,

When you put the sample in the fridge, was it covered? If it was in the fridge, uncovered for a while, some of the liquid might have evaporated which would give you a high gravity reading.

Also, if you haven't pitched your yeast yet, perhaps you have an infection that has started to chew through the wort.

Out of interest, why were you taking two OG readings?

Andrew

Hi Andrew

The sample was uncovered but I'd be surprised if much evaporated. The yeast was pitched as I was running the cooled wort into the fermenter, all within an hour of flameout, so I wouldn't think that anything could have started munching on the malty goodies and lowering the SG. I take two OG readings: 1 to check the efficiency of my mashing/sparging regime and the second one to check OG into the fermenter (the last being the 'true' OG I guess).

Cheers

Neil

 

[Mr.Moonshine]

Was there a temperature difference between the samples of the two OG's?
If you were running it into the boiler at 15 degrees and your hydrometer is calibrated to 20, that would give you a higher than usual gravity reading.
Similarly, if your hydrometer is calibrated to 15 degrees (as some are, mine is calibrated to 20 I beleive), then having the sample at 20 would give you a lower gravity reading, as the heat made the sample more viscous.

Cheers,

Mr.Moonshine

 

[QldKev]

Welcome to the world of chemistry. Brix is the refraction of light. Dissolved solids, including sugar will cause refraction to occur. Now the theory is you measure the brix of your wort to calculate dissolved sugars, but what about the other solids in the wort? Filtering the sample prior to measuring the brix will help get a more accurate reading, but without also measuring the pol (apparent sucrose content as measured by the polarisation method) you are only using a best guess. Purity is the ratio of sucrose (or pol) to the total soluble solids (brix) in a sugar product.

So you could have had a higher reading pre boil as all the other solids etc are stirred up at that stage; and now the impurities have settled out of suspension.
Also the ambient temperature does comes into play. The brixometer is normally calibrated at 20c.

Generally in homebrewing the amount of other impurities we are measuring into the sample is fairly consistent, so we can use a sample that is unfiltered, but we should be careful to compare samples that are from the same level of being mixed.

Sorry if I got a bit of topic; and yes I have worked in the sugar industry.

QldKev

 

[apd]

Hi Andrew

The sample was uncovered but I'd be surprised if much evaporated. The yeast was pitched as I was running the cooled wort into the fermenter, all within an hour of flameout, so I wouldn't think that anything could have started munching on the malty goodies and lowering the SG. I take two OG readings: 1 to check the efficiency of my mashing/sparging regime and the second one to check OG into the fermenter (the last being the 'true' OG I guess).

Cheers

Neil

So the SG (specific gravity) you take to check the efficiency of your mashing/sparging regime is prior to the boil and the other one is after the boil?

In that case you are getting readings that are to be expected. The boil evaporates some of the liquid (3L in your case) which concentrates the wort which means the SG will go higher.

Or have I misunderstood what you're saying?

By the way, I think there's only one OG. That's the SG reading that is taken after the boil, before fermentation. The SG you take after mash, before boil is called the pre-boil gravity.

Andrew

 

[bigfridge]

Hi Andrew

The sample was uncovered but I'd be surprised if much evaporated. The yeast was pitched as I was running the cooled wort into the fermenter, all within an hour of flameout, so I wouldn't think that anything could have started munching on the malty goodies and lowering the SG. I take two OG readings: 1 to check the efficiency of my mashing/sparging regime and the second one to check OG into the fermenter (the last being the 'true' OG I guess).

Cheers

Neil

Once the wort has started to ferment you have to correct the reading due to the presence of Alcohol. You should get back to whoever sold you the uinit and ask them for proper instructions, otherwise there are plenty of info available on the net.

 

[matho]

you have to remember that when you boil you get hot break and when you cool you get cold break before both processes they are disolved solids which would add to the SG of the wort.

cheer's matho

 

[buttersd70]

Andrew, the OP states that his post boil gravity is lower than his preboil gravity. Which is of course the opposite as to what should occur. Hence his perplexed question.

edit: I end to think it's likely an error in one of the readings.

 

[cdbrown]

edit: I end to think it's likely an error in one of the readings.

or failed to adjust the readings properly based on the temp.

 

[Kai]

Welcome to the world of chemistry. Brix is the refraction of light. Dissolved solids, including sugar will cause refraction to occur. Now the theory is you measure the brix of your wort to calculate dissolved sugars, but what about the other solids in the wort? Filtering the sample prior to measuring the brix will help get a more accurate reading, but without also measuring the pol (apparent sucrose content as measured by the polarisation method) you are only using a best guess. Purity is the ratio of sucrose (or pol) to the total soluble solids (brix) in a sugar product.

So you could have had a higher reading pre boil as all the other solids etc are stirred up at that stage; and now the impurities have settled out of suspension.
Also the ambient temperature does comes into play. The brixometer is normally calibrated at 20c.

Generally in homebrewing the amount of other impurities we are measuring into the sample is fairly consistent, so we can use a sample that is unfiltered, but we should be careful to compare samples that are from the same level of being mixed.

Sorry if I got a bit of topic; and yes I have worked in the sugar industry.

QldKev

I don't think dissolved solids would be the issue here, firstly because if it was then a lot more people would experience this problem. Secondly, I thought the MOS (material other than sugar (I like making up acronyms)) had to be *dissolved* to affect the refraction; in my experience undissolved solids just make the reading blurrier.

My take is that it was just a misread or sampling error... perhaps the preboil sample was taken when the runnings had not mixed properly?

If evap rate hadn't been mentioned, I'd ask if it was raining heavily on the day

 

[QldKev]

I don't think dissolved solids would be the issue here, firstly because if it was then a lot more people would experience this problem. Secondly, I thought the MOS (material other than sugar (I like making up acronyms)) had to be *dissolved* to affect the refraction; in my experience undissolved solids just make the reading blurrier.

My take is that it was just a misread or sampling error... perhaps the preboil sample was taken when the runnings had not mixed properly?

If evap rate hadn't been mentioned, I'd ask if it was raining heavily on the day

lol at the MOS, I though I was back at work in IT.

As far as undissolved solids I will quote an email from the Chief Chemist where I used to work (in the sugar industry), when I asked him about Brix in homebrew; he was also a fellow homebrewer.

"The colour of the liquid in the refract will not affect the reading but the amount of shit in it will.
The liquid needs to be clarified / filtered properly for it to work.
So that is where the variation is most likely coming from"

This email is from a discussion when I tested some brew through the brixometer at work (now ex work, I left for a new job) when I was programming the interface, the brixometer is an automated, very expensive piece of gear to measure the brix. It has built in temperature compensation, does three samples blah blah blah... it is one of the key devices that based our payment to the growers from... I actually had varying (slightly) readings when I was playing with it over the day. I had not filtered my sample.

So by the time you allow from pre-boil to post boil it should concentrate; but then you add into clarifying, and then a bit of fermentation I think I can justify the reduction of the brix reading read.

But also as Kai says (who I consider one of the more senior posters, so good advice) , we don't normally get a huge variation in the real world as we are generally within a pretty limited environment.

QldKev

 

[NeilArge]

lol at the MOS, I though I was back at work in IT.

As far as undissolved solids I will quote an email from the Chief Chemist where I used to work (in the sugar industry), when I asked him about Brix in homebrew; he was also a fellow homebrewer.

"The colour of the liquid in the refract will not affect the reading but the amount of shit in it will.
The liquid needs to be clarified / filtered properly for it to work.
So that is where the variation is most likely coming from"

This email is from a discussion when I tested some brew through the brixometer at work (now ex work, I left for a new job) when I was programming the interface, the brixometer is an automated, very expensive piece of gear to measure the brix. It has built in temperature compensation, does three samples blah blah blah... it is one of the key devices that based our payment to the growers from... I actually had varying (slightly) readings when I was playing with it over the day. I had not filtered my sample.

So by the time you allow from pre-boil to post boil it should concentrate; but then you add into clarifying, and then a bit of fermentation I think I can justify the reduction of the brix reading read.

But also as Kai says (who I consider one of the more senior posters, so good advice) , we don't normally get a huge variation in the real world as we are generally within a pretty limited environment.

QldKev

Thanks everybody for the thoughtful and constructive feedback. The only thing I can think of is that I may have used two different hydrometers to take the SG readings and one is a bit out relative to the other. To be honest, I have never had this happen before, so it doesn't appear to be something systemic in my brewing process (i.e. most things are done the same from brew to brew). Even when I have had poor efficiency due to channelling during sparging, or not boiling hard enough for long enough I have never had the 'pre-boil gravity' higher than the OG. I think I'll go an test those hydrometers now. Yesterday, the pre-boil gravity wort and the wort running into the fermenter were at the same temp.

Thanks and cheers :icon_cheers:

Neil (aka ToG)

 

[gregs]

I must say that I know this QldKev and he is a very unassuming fella when first met, then you realise he is very, very clever. So much so that, you need to listen to his kind.

 

[apd]

Andrew, the OP states that his post boil gravity is lower than his preboil gravity. Which is of course the opposite as to what should occur. Hence his perplexed question.

edit: I end to think it's likely an error in one of the readings.

My bad. My very, very bad. Apologies for wasting bandwidth.

Andrew

 

[Kai]

Thanks everybody for the thoughtful and constructive feedback. The only thing I can think of is that I may have used two different hydrometers to take the SG readings and one is a bit out relative to the other. To be honest, I have never had this happen before, so it doesn't appear to be something systemic in my brewing process (i.e. most things are done the same from brew to brew). Even when I have had poor efficiency due to channelling during sparging, or not boiling hard enough for long enough I have never had the 'pre-boil gravity' higher than the OG. I think I'll go an test those hydrometers now. Yesterday, the pre-boil gravity wort and the wort running into the fermenter were at the same temp.

Thanks and cheers :icon_cheers:

Neil (aka ToG)

Two different hydrometers would definitely be a potential cause, it would be good to know if they read differently or not. It's not that hard for the piece of paper to slip up or down inside that glass tube.

 

[buttersd70]

My bad. My very, very bad. Apologies for wasting bandwidth.

Andrew

Apologies for 'wasted bandwidth' is not required....just as a sarcastic response to a polite (and subdued) clarification of the OP's actual question is also not required.

 

[manticle]

I thought the apology was genuine as he realised he'd completely misread the original post?

I've been wrong before but today is my birthday which makes me infallible.

 

[Kai]

::berfday::