SG of mash vs SG of wort

[abrewhal]

Does boiling mash increase SG?
Some youtube videos I've been watching always take a SG measurement of the mash, is the SG measurement of mash the same measurement you get after boil?
If not, why even take a SG measurement for the mash?

 

[VikeMan]

The gravity increases as you boil away water and the sugars/dextrins become more concentrated. A reason to measure gravity before the boil might be to see if the gravity is where it's expected to be at that stage (i.e. the pre-boil gravity target), and if it's not (say it's lower than expected), plan extra boil time or the addition of malt extract to make up the difference.

 

[mac_1103]

SG will increase as volume decreases through boil-off. Pre-boil SG tells you (roughly) how efficiently you got sugar out of your grains. If you don't hit your pre-boil SG target then you won't hit your post-boil SG target either. Recipe building software will give you both numbers.

 

[DBhomebrew]

Pre-boil Vol * Gravity = Post-boil Vol * Gravity

5.5G * 1.050 = 5G * 1.055

5.5 * 50 = 5 * 55

275 = 275

It's the gravity  points that stays constant, not the specific gravity.

 

[AlexKay]

Currently doing a barleywine. Been boiling all afternoon:

4 G * 1.048 = 1.5 G * 1.128

 

[mac_1103]

So is it done yet?

 

[AlexKay]

Hit 1.128 exactly. Pretty good considering the 1.5 G was a rough estimate.