What is causing the change in Specific Gravity?

[RocketBee]

Before I pitched the yeast, I stirred the must thoroughly and took a reading which showed a starting specific gravity of 1.098. While waiting for the must to drop a few degrees before I pitched the yeast, I remeasured a little while later and the S.G. climbed back up to 1.100. Thinking that I "mis-measured", I repeated the process. I stirred the must thoroughly came up with 1.098, then a little while later, back up to 1.100. I'm taking the reading directly in the 6-gallon fermentation bucket, not using a test beaker.

Am I seeing things...doing anything wrong? What's causing the delta and what do I use for starting S.G?

Thanks and Happy New Year!

 

[crabjoe]

This is a guess and it's assuming you're not miss reading what you're seeing...

1st hydrometer is actually measuring the density of the liquid, not just the sugar level. It seems like your must is separating.. and something thicker is moving to the top, causing the hydrometer to float different. Think of it like oil in water... sure you can mix it to get a more even density throughout, but once you stop shaking it, the water will go drop and the oil will float to the top...

That's my guess and I hope it helps.

 

[cmason1957]

I think @crabjoe might be on to something. I mix up my kits and then stir rather vigorously with the three-pronged degassing tool. and then wait until the next day to take my initial reading. I always take my initial readings in the fermentation bucket, since I'm not all that interested in exactly what it is, just ballpark, both upper and lower numbers. It could be that you are at slightly different angle and read it just slightly differently we are only talking a .002 change in the reading, which is certainly within the error in reading bracket, when reading inside the bucket.

 

[bshef]

Temperature affects SG reading. There are conversion tables included with hydrometers and on the internet.; that probably accounts for the minute changes as well.

 

[salcoco]

the must could be releasing sugar also.I would vote for misreading based on viewing angle. go with which either reading you prefer. one way to verify fill measurement jar with the must liquid after minor filtering through a cloth take that reading as gospel.

 

[Rocky]

We are only talking about a variation in ABV of about 0.25%. What is the variation is on store bought wines that say "13% ABV?" How many wines are exactly 13% ABV? ABV is an analog value, not a digital value, so there are none!

 

[cmason1957]

We are only talking about a variation in ABV of about 0.25%. What is the variation is on store bought wines that say "13% ABV?" How many wines are exactly 13% ABV? ABV is an analog value, not a digital value, so there are none!

Commercial wines are allowed to be +/- 0.5% on ABV, so that 13% could be 12.5 - 13.5 %. In reality the conversion numbers we use to determine ABV from Hydrometer readings are not within that tolerance, so why worry about it, is certainly true.

 

[BernardSmith]

Readings based on hydrometers are fundamentally unreliable and inaccurate. First, your hydrometer measures in increments of 2 points, then you take a reading where your eye is unlikely to be horizontal to the surface of the liquid and then you have to account for how level the container is. If your reading is accurate to 0.5% of ABV you are doing exceptionally well. In short, as long as your readings are in the same ballpark I wouldn't lose a moment's sleep over this. The tool works well enough but it is from a technology that is almost 2000 years old (though, 2000 years ago they tended to look at how high an egg would float in the must rather than glass tubes with weights on one end). A reading gives you a false sense of accuracy which is why it is quite funny when someone claims that they just bottled a wine at 10.38% ABV (they meant 10%)...

 

[RocketBee]

Thanks for all the great responses and since I really like history @BernardSmith I think yours is the best...really provided some needed perspective for the neophyte that I am.

 

[BernardSmith]

There are some really fascinating mead recipes available on line that come from the middle ages when eggs were still being used to estimate the equivalence of what we refer to today as the starting specific gravity of the must (the fermentable solution). The thing is, the freshness of the egg (how much air is trapped in egg), how large the egg, etc would make this tool very subjective but for hundreds of years people have been making wine and mead. That said, even when these drinks were being made by master wine makers who served the whims of the powerful not every batch made was a success, largely because those making wines and meads (and brewing beers) knew what to do but they did not really know why they did what they did, only that what they did worked ... unless it didn't. Heck! Yeast was discovered to be an organism by Pasteur only in 1859. In some cultures before that if you were a wine maker you might have brought a new fermenting container to meet the older ones so that the new one would eventually learn how to ferment. But that's anthropology , not so much history, though it does highlight how humans have understood wine making. In short, you may be a novice but it's the yeast that do the heavy lifting. Our job is to stand back and let the yeast get on with their job, though sometimes the yeast need us to remove an obstacle or two so that they can do what they do best but at the end of the day it's always us that take all the credit.

 

[Scooter68]

By the way, It takes a huge change in temp to affect the SG readings significantly. Using a Hydrometer calibrated for 60 degrees Fahrenheit - a wine at 90 degrees temp Fahrenheit would in fact be 1.1004 and of course spoiled very quickly at that temp. If that same wine was measured at a temp of 40 degrees Fahrenheit the actual Sg would be 1.099

For that reason I never bother with trying to do a temp correction with my wine batches. The differences are not enough to worry about - I'd be more worried about the wines temperature than an SG reading at either of those temps.

(You can check those numbers here: https://www.brewersfriend.com/hydrometer-temp/

 

[pillswoj]

Also keep in mind that the hydrometers for wine makers for $10-20 (buy 2 for when you break one) are not that accurate to begin with. Real laboratory grade reference hydrometers go for $100 or more each, alcohol hydrometers for regulatory are in the $400 range.

I would not worry about reading differing by .002 or so at all

 

[crabjoe]

Also keep in mind that the hydrometers for wine makers for $10-20 (buy 2 for when you break one) are not that accurate to begin with. Real laboratory grade reference hydrometers go for $100 or more each, alcohol hydrometers for regulatory are in the $400 range.

I would not worry about reading differing by .002 or so at all

This got me laughing. Not because I disagree with you, but because I think the ones I have are off... I say that because I gave a few different wines I had made to friend of mine that's a regular drinker. What I got from her was "you're wine really sneaks up on you." As to say she's sure it's got more alcohol that what I had printed on the labels.

Mind you, the calculation I'd bee using was:

ABV = (og – fg) * 131.25

I think I might need to switch to the below to maybe make it a bit more accurate:

ABV =(76.08 * (og-fg) / (1.775-og)) * (fg / 0.794)

 

[sour_grapes]

I think I might need to switch to the below to maybe make it a bit more accurate:

ABV =(76.08 * (og-fg) / (1.775-og)) * (fg / 0.794)

Do you have some sort of reference for this other formula?

 

[crabjoe]

Do you have some sort of reference for this other formula?

https://www.brewersfriend.com/2011/06/16/alcohol-by-volume-calculator-updated/

Snippet: "The complex formula, and variations on it come from Ritchie Products Ltd, (Zymurgy, Summer 1995, vol. 18, no. 2) -Michael L. Hall’s article Brew by the Numbers: Add Up What’s in Your Beer, and Designing Great Beers by Daniels."

 

[sour_grapes]

https://www.brewersfriend.com/2011/06/16/alcohol-by-volume-calculator-updated/

Snippet: "The complex formula, and variations on it come from Ritchie Products Ltd, (Zymurgy, Summer 1995, vol. 18, no. 2) -Michael L. Hall’s article Brew by the Numbers: Add Up What’s in Your Beer, and Designing Great Beers by Daniels."

Thank you.

 

[Scooter68]

OR... you could simply use Brewer's Friend Online calculator The one they refer to in the link posted by crabjoe, and let it do the math for you.