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Why do we measure SG/PA/Brix ?

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arcticsid

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If these measurements are all related to the same thing, than why do we use all three different terms in measuring what is ultimately going to be the final alcohol content?

How are they different, and what can they TELL us differently?

Seth brought this up and I think it is a good question.

When I start a wine, I measure the SG and the PA I can expect out of it if it ferments out. But I use the SG to measure the progress, but can just as easily look on the other side of the hydrometer, see the PA, do the math and come up with the same numbers.

Anyone?
 

Tom

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Brix is used when you have a refractometer. This is used in the field to ck the sugar level in fruit / grapes on the vine. It tells you when to pick at the right sugar level.
PA is just a easy way to convert the SG to know what the alcohol will be. Sure beats a math equation to figure it out right?
 

arcticsid

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We get that. But why do we always say, "my starting SG is 1.0xx", and not "my starting PA is around 13%?"

We all know they are the same but, just a drinking question.
 

Tom

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What U been drinking...LOL
SG is more accurate Now what about"Plato" thats another way to measure
 

seth8530

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I personally prefer the ABV scale. But maybe by using specific gravity we can all make ourselves to appear smarter lol. That way if the wife or GF ask we can say that we have been studieng for out chemistry final lol Just a thought
 

ashappar

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PA is fine as a start measurement if you ferment to completely dry. But if not fermented to completely dry then original gravity and finish gravity to determine ABV

you could just say its convention, quoting SG when discussing the wine stats. Monkey see monkey do etc, but its also convenient to use a number besides PA when discussing not only the start but other points along the ferment before the end.
 

seth8530

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I like your idea on why people use the "monkey see monkey do method" but PA is just as effective and much more descriptive on how much sugar is left in the wine than a series of numbers. even during fermentation. That is just my view on it anyways.
 

ashappar

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hrm, but what if you say :

pitch yeast at 13%
transfer to secondary at 2%

PA is confusing in that context
where SG is not.
 

seth8530

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I dunno that makes sence to me. I Started at 13 percent. Fermented down to 2 percent before i racked it into a secondary. I guess its kinda like toilet paper. There are two ways to hang it and they both get the job done.. but only one way is the right way.....
 

Wade E

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Tom is right in staing that the SG scale is much more accurate then the PA scale. The third measures how much sugar is in 1 liter. I myself only really use sg but will be using my refractometer now that I have one so that will change.
 

seth8530

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I guess the gravity scale is more important if being very exact on measurments is very important to you.
 

ashappar

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I dunno that makes sence to me. I Started at 13 percent. Fermented down to 2 percent before i racked it into a secondary. I guess its kinda like toilet paper. There are two ways to hang it and they both get the job done.. but only one way is the right way.....
cheers, use PA if you like.
when I see it, I think "Potential Alcohol"
so seeing it more than once, seeing it decrease.. confuses me a bit.
I probably hang my TP the wrong way also. :p

my hydrometer has more ticks on the SG scale, so I can get a better reading as well. but to each his own!
 

djrockinsteve

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I dunno that makes sence to me. I Started at 13 percent. Fermented down to 2 percent before i racked it into a secondary. I guess its kinda like toilet paper. There are two ways to hang it and they both get the job done.. but only one way is the right way.....
Somebody did research (and our Gov't. probably paid for it) to which way is the best way to hang toilet paper. The under way will cause you to use more than if you removed T.P. that was placed on the over way. It's based upon how it tears.

All I know is when I hear the spindle roll over and over I just want to scream "How much do you need" or "Maybe you need to eat more vegetables". The following noise heard is the flush with that deep Glug Glug which means there's gonna be another flush, or two.

Do I sound like my parents? Oh and by the way I did walk uphill bothways to catch the school bus!:)
 

Tom

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If you make BEER you will NEVER ferment dry like in wine. So, to figure out the alcohol you need the starting and ending gravity to figure the alcohol in BEER.
 

arcticsid

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never knew that TOM, As you know I don't know much about making beer, but that makes good sense. But, explain to me, if I want my beer to end up at 7%, I still start with an SG of "x". Can't I get this same PA by looking at the other side of the hydrometer?

While we are on the subject, I have never seen the word sorbate mentioned in beer making.

I don't want to turn this thread into a beer making discussion, by why is that?

Got me curious now.
 

seth8530

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If you make BEER you will NEVER ferment dry like in wine. So, to figure out the alcohol you need the starting and ending gravity to figure the alcohol in BEER.
Why cant you just say i want to start out at say 6 PA and end at 1.5 % pa?
 

Tom

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never knew that TOM, As you know I don't know much about making beer, but that makes good sense. But, explain to me, if I want my beer to end up at 7%, I still start with an SG of "x". Can't I get this same PA by looking at the other side of the hydrometer?

While we are on the subject, I have never seen the word sorbate mentioned in beer making.

I don't want to turn this thread into a beer making discussion, by why is that?

Got me curious now.
NO sorbate used.
The yeast only ferments so much. It all depends on which yeast you use and TEMP.
Sorbate is NOT needed in beer. Now you can use nutrient but not clearing agents. Time will clear beer. Remember you want carbonation so some yeast is in most homebrews before adding sugar to bottle combornate. OR kegging like me and Wade.
 

ashappar

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Somebody did research (and our Gov't. probably paid for it) to which way is the best way to hang toilet paper. The under way will cause you to use more than if you removed T.P. that was placed on the over way. It's based upon how it tears.

All I know is when I hear the spindle roll over and over I just want to scream "How much do you need" or "Maybe you need to eat more vegetables". The following noise heard is the flush with that deep Glug Glug which means there's gonna be another flush, or two.

Do I sound like my parents? Oh and by the way I did walk uphill bothways to catch the school bus!:)
And if you aren't using both sides of the TP you are only 50% efficient. Waste!

Why cant you just say i want to start out at say 6 PA and end at 1.5 % pa?
PA = potential alcohol, right?
so its the first reading, before you pitch yeast.
its your potential ABV, if you ferment to dry.

why continue to say PA? your potential doesnt go from 6 to 1.5. It was always 6. Is the issue that your hydrometer only has a PA scale?

jack keller gives you some support (link) - you can use PA if thats all you have :

The potential alcohol scale typically reads from 0 to 16%. Using the standard hydrometer, you cannot measure the alcohol in a finished wine. But you can measure the P.A. before the yeast is added and measure it again after fermentation is complete. By simple subtraction, the P.A. lost is the percentage of alcohol in the finished wine.

per Toms suggestion - I may switch to the more obscure Plato. Now if they just made a quadruple scale hydro that included the Plato.
 

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