New Giveaway - Wort Monster Conical Fermenter!

Home Brew Forums > Home Brewing Beer > Brew Science > Hot break & specific gravity?




Reply
 
LinkBack Thread Tools Display Modes
Old 08-31-2012, 02:52 PM   #1
sroberts
Feedback Score: 0 reviews
Recipes 
 
Join Date: Sep 2011
Location: Peachtree City, GA
Posts: 60
Liked 7 Times on 5 Posts
Likes Given: 18

Default Hot break & specific gravity?

I understand the pre-boil to post-boil gravity of wort is directly proportional to the amount of boil-off... same qty of sugar, less water.

Why doesn't the fall-out of proteins from the wort affect the gravity? During boil a lot of material drops out of the fluid. Suppose we replaced the water lost during boil - after the boil the fluid appears less dense as evidenced by the hot break fall-out and increased clarity. Apparently the material that fell out of the wort didn't contribute to the gravity in the first place? If that's the case, what is different about the nature of the material that was removed?



__________________
sroberts is offline
 
Reply With Quote Quick reply to this message
Old 08-31-2012, 03:25 PM   #2
drewmedic23
HBT_SUPPORTER.png
Feedback Score: 2 reviews
Recipes 
 
Join Date: Aug 2012
Location: Jackson, NJ
Posts: 162
Liked 4 Times on 4 Posts
Likes Given: 3

Default

I've never really thought about that. Well to start off, the hydrometer will measure the SG of a liquid in which the particles are in suspension....IOW if you take some sand and throw it in the liquid and then measure the SG, it will be the same because it just drops to the bottom. I would have to say that the proteins dont contribute much to the SG so there is no noticable change. When I take my OG reading, I do it right before I pitch the yeast and take the wort right off of the top of my fermentor (after I have strained out any hops or grain particles leftover). When I take my FG, I get a reading right out of the bucket before priming sugar. I guess there is no way to account for the sediment in your gravity readings short putting it in a centrifuge. Good question though, I am curious to see what other people say



__________________
drewmedic23 is offline
 
Reply With Quote Quick reply to this message
Old 08-31-2012, 07:05 PM   #3
ajdelange
Senior Member
HBT_SUPPORTER.png
Feedback Score: 0 reviews
Recipes 
 
Join Date: Aug 2010
Location: McLean/Ogden, Virginia/Quebec
Posts: 5,208
Liked 452 Times on 371 Posts
Likes Given: 13

Default

Quote:
Originally Posted by sroberts View Post
Why doesn't the fall-out of proteins from the wort affect the gravity?
Well it does, of course. Anything dissolved in the wort, be it sugar, protein, hops acids, minerals, is measured as 'extract' by a hydrometer or density meter. If something precipitates during some part of the process, be it calcium phosphate, calcium carbonate, or coagulated protein it reduces the extract.

Quote:
Originally Posted by sroberts View Post
During boil a lot of material drops out of the fluid. Suppose we replaced the water lost during boil - after the boil the fluid appears less dense as evidenced by the hot break fall-out and increased clarity.
I don't follow that. After the boil the wort is more dense. Or do you mean it would be less dense if you replaced all the water boiled off? It would be less dense in that case because you have dropped material, i.e. the protein (and any salts that precipitated).

Quote:
Originally Posted by sroberts View Post
Apparently the material that fell out of the wort didn't contribute to the gravity in the first place? If that's the case, what is different about the nature of the material that was removed?
I must be dense because I really cannot understand how you have concluded this.

BTW when one analyzes beer he takes a precisely measured volume (100 mL), adds some water to that, boils it down to about 50 mL (collecting the vapor which contains all the alcohol) reconsititutes to 100 mL and measures the density of the reconstituted beer. Protein precipitates during the boil and so is not measured when the density determination is done. This results in a true extract estimate which is low because some of the extract has been removed. But in this case it hasn't really beacause it tends to float about in the flask i.e. its density is about the same as that of the reconsitituted beer. Thus it would be displaced by a hydrometer or could enter the density meter U-tube without throwing the reading off and thus, in this case, the loss of protein does not count appreciably. In the kettle the protein globs are a little heavier than the wort because they sink to the bottom eventually but not by much so the error is small.
__________________
ajdelange is offline
 
Reply With Quote Quick reply to this message
Old 08-31-2012, 08:43 PM   #4
sroberts
Feedback Score: 0 reviews
Recipes 
 
Join Date: Sep 2011
Location: Peachtree City, GA
Posts: 60
Liked 7 Times on 5 Posts
Likes Given: 18

Default

Quote:
Originally Posted by ajdelange View Post
do you mean it would be less dense if you replaced all the water boiled off? It would be less dense in that case because you have dropped material, i.e. the protein (and any salts that precipitated).
So if I replace the water boiled off, my post-boil gravity should be less than my pre-boil gravity due to material that dropped out of solution? That's what I'm wondering because it is commonly reported that post-boil gravity can be calculated from pre-boil gravity by simply adjusting for boil off, using a formula such as
[1,000 x (PreBG - 1)] x [PreBV/PostBV] = (PostBG/1000) +1

Ex:
6 gal @ 1.050: 6 * 50 = 300 "points" pre-boil
Boiling down to 5 gals results in 1.060, 300 / 5

But that formula does not account for the protein dropped during the boil. So does the protein content not affect the gravity, or is its effect just insignificant?
__________________
sroberts is offline
 
Reply With Quote Quick reply to this message
Old 08-31-2012, 09:28 PM   #5
ajdelange
Senior Member
HBT_SUPPORTER.png
Feedback Score: 0 reviews
Recipes 
 
Join Date: Aug 2010
Location: McLean/Ogden, Virginia/Quebec
Posts: 5,208
Liked 452 Times on 371 Posts
Likes Given: 13

Default

Quote:
Originally Posted by sroberts View Post
So if I replace the water boiled off, my post-boil gravity should be less than my pre-boil gravity due to material that dropped out of solution?
Yes. Mass is conserved. You have water, protein, minerals and sugar in a wort. You boil. Some water flies off as vapor. Some minerals precipitate as does some protein. You replace the water. You now have the same sugar and water but somewhat less protein and minerals. The wort now weighs less than it did and as the volume is the same the density is less.

Quote:
Originally Posted by sroberts View Post
That's what I'm wondering because it is commonly reported that post-boil gravity can be calculated from pre-boil gravity by simply adjusting for boil off, using a formula such as
[1,000 x (PreBG - 1)] x [PreBV/PostBV] = (PostBG/1000) +1
That's an approximation because the mass of salts and protein lost is small. Note that the formula is also an approximation because 'points' are not linearly related to mass (though they are nearly so).



Quote:
Originally Posted by sroberts View Post
But that formula does not account for the protein dropped during the boil. So does the protein content not affect the gravity, or is its effect just insignificant?
It's not significant compared to errors in measurement of volume, measurement of density, errors in assuming points are a measure of mass etc.
__________________
ajdelange is offline
sroberts Likes This 
Reply With Quote Quick reply to this message
Old 09-02-2012, 08:08 PM   #6
sroberts
Feedback Score: 0 reviews
Recipes 
 
Join Date: Sep 2011
Location: Peachtree City, GA
Posts: 60
Liked 7 Times on 5 Posts
Likes Given: 18

Default

Thanks for the info!



__________________
sroberts is offline
 
Reply With Quote Quick reply to this message
Reply


Quick Reply
Message:
Options
Thread Tools
Display Modes


Similar Threads
Thread Thread Starter Forum Replies Last Post
Lactic Acid and Specific Gravity Bsquared Brew Science 6 05-09-2013 03:04 AM
Can someone help me break this down? Pugs13 Brew Science 23 03-02-2012 11:58 PM
Specific gravity after brewing and after priming. adamant Brew Science 7 08-26-2011 02:46 AM
Brix to Specific Grav confusion christoph200071 Brew Science 3 06-06-2011 01:02 PM
NO hot break?? beerman77 Brew Science 8 12-15-2009 03:07 PM