Measure OG without hydrometer?

[Shalenkur]

I busted my hydrometer last night. Tried hot glue this morning LOL didn't work.
So,
I measured
out 100ml of water and 100ml of wort.
The water weighs 97 grams, and the wort weighs 102 grams.
102/97=1.0515 OG
Am I correct?

 

[DBhomebrew]

I'm not sure about the premise, but 100ml of water should be 100g.

 

[IslandLizard]

I busted my hydrometer last night. Tried hot glue this morning LOL didn't work.
So,
I measured
out 100ml of water and 100ml of wort.
The water weighs 97 grams, and the wort weighs 102 grams.
102/97=1.0515 OG
Am I correct?

Good idea and not too bad an approximation, as long as you got the exact same volumes when weighing. At a nominal 100 ml volume, 1 ml more or less throws it [Edit for clarity] the SG off by around 10 points...

For high(er) accuracy you would need a volumetric flask. It's the one with the long neck and an etched line at the volume mark. Mind the measuring/calibration temp too.

 

[Vale71]

I'm not sure about the premise, but 100ml of water should be 100g.

Whatever he's using to measure volumes is clearly not very accurate. This is however irrelevant provided he uses the same vessel to measure and weigh both water and wort and then calculates the ratio like he presumably did.

For high(er) accuracy you would need a volumetric flask. It's the one with the long neck and an etched line at the volume mark. Mind the measuring/calibration temp too.

Nope, he just needs to use the same flask for both measurements (see above). Temperature should definitely be as close as possible to 20°C although a couple of degrees more or less is only going to affect the fourth or fifth decimal digits, so no big deal.

 

[Shalenkur]

Ok thanks for the replies! Both samples were 48 degrees F.
So the formula is correct?

 

[DBhomebrew]

Seems like yes, as long as your volumetric measuring is consistent if not accurate.

ETA: I'd measure out another "100ml" of water and see where you're at.

 

[Qhrumphf]

As specific gravity is a ratio, if your volumes were truly identical, whatever they are, it should be accurate. But as said, temp matters a little bit. However volumes matter a LOT since it's only a few percent difference you're looking to measure (think of it this way- if we assume your measurements are correct your wort is only 5.15% heavier than water). If you had 101ml if one and 99ml of the other (where you've thrown each one off by circa 1%), you've thrown your calculation off by a pretty noticeable number.

 

[bruce_the_loon]

The formula is the the density of the sample divided by the density of water at 20°. Units don't matter as long as the volumes and measurements are the same. As it is a ratio, if the volume is out, e.g your beaker/flask is out by 3ml, as long as you use the same flask/beaker filled to an identical level, then it will work.

There's a trick for eliminating volume verification by the Mk.1 eyeball. If you have a small bottle with a tight lid, first weigh it empty to get the tare mass, submerge it in the water to fill it completely, close the lid and then rinse and dry the outside before weighing it again to get the gross mass. Gross mass - tare mass is the nett mass of the liquid inside. Empty the bottle, make sure you get all the drops out or dry the inside somehow and repeat with the wort.

As the volumes should now be identical and at 20°, you can use the simple mass sample/mass water you suggested first.

 

[chipmunk]

You could also use an empty beer bottle as a DIY volumetric flask - just fill and mark a level on the neck. Like a volumetric flask, filling to a line on the skinny neck will provide a more accurate relative reading than a line on say a mason jar. The other advantage... emptying out that beer bottle!

 

[IslandLizard]

You could also use an empty beer bottle as a DIY volumetric flask - just fill and mark a level on the neck.

I'd fill the bottle to the very top, and leave the surface skimmed flat, even with the top of the rim. Much more precise than eyeballing a meniscus at a drawn line or edge of a piece of tape. The small(er) the diameter, the less(er) the effects of small volume misreadings.

At a long neck's nominal 330 ml volume, a 1 ml difference between the 2 measured volumes equates to a 3.3 point deviation of SG.

 

[chipmunk]

In the name of science, I opened a beer and measured a beer bottle opening at 1.6cm - so area is around 2cm2. So that 1ml (=1cm3) difference would rise the liquid in the neck level around 5mm. So not bad accuracy - 0.6 deviation in SG per mm of level.

 

[Shalenkur]

I used a graduated cylinder, but as was said, it makes more sense to fill it or a bottle all the way up for consistency.

Does this work for FG?

Thanks everyone!

 

[bruce_the_loon]

I used a graduated cylinder, but as was said, it makes more sense to fill it or a bottle all the way up for consistency.

Does this work for FG?

Thanks everyone!

No reason why it would not work in theory, you're still measuring the mass of a known volume to get density. The problem would be if your scale isn't accurate enough to differentiate between fractional grams. For example, a 1.004 FG is 0.4g difference on a 100ml sample. So if your scale only reads grams, you would either not see the 0.4g at all, or it might report it as 101g instead.

 

[Silver_Is_Money]

You are making a homemade Pycnometer. The real thing is very inexpensive (about $20-30 for some nice ones on Amazon). To get technical, they measure density as opposed to specific gravity. Much higher precision than a hydrometer if your scale is precise enough and you get one with a thermometer built into the plunger/excess_expeller. Identical temperatures are highly critical for this method to yield valid results. I'm shocked that they are not even minimally popular among home brewers, as they are at least potentially much better than a hydrometer, and don't cost any more than a hydrometer. Precise calibration requires distilled water. Effort is likely the reason why they are not popular.

Instructions and technical stuff here:
https://idoc.pub/documents/density-determination-by-pycnometer-k6nq6g0w19lw

 

[Karn]

I busted my hydrometer last night. Tried hot glue this morning LOL didn't work.
So,
I measured
out 100ml of water and 100ml of wort.
The water weighs 97 grams, and the wort weighs 102 grams.
102/97=1.0515 OG
Am I correct?

I don't know if that formula is correct. It looks good, but everything does on that level. Anyway, I think just the relativity of the two weights provides enough information and it's OK that the water weight indicates 97 grams because it is relative. As long as you weigh each (water and wort) each time you'll get accurate information even though the weights aren't really accurate. The wort weighs five more grams than the water, so something is still going on. Was your measurement of the mL's accurate?

 

[chipmunk]

You are making a homemade Pycnometer.

That is very cool. How about a Beer bottle, filled to the brim, then put a marble (larger than the opening) on top - the curve of the sphere should displace some of the liquid like similar to the store bought ones. I guess it’s down to the accuracy of your scale then...

 

[Silver_Is_Money]

That is very cool. How about a Beer bottle, filled to the brim, then put a marble (larger than the opening) on top - the curve of the sphere should displace some of the liquid like similar to the store bought ones. I guess it’s down to the accuracy of your scale then...

I think that should work!

 

[chipmunk]

You are making a homemade Pycnometer.

That is very cool. How about a Beer bottle, filled to the brim, then put a marble (larger than the opening) on top - the curve of the sphere should displace some of the liquid like similar to the ones. I guess you’re down to the accuracy of your scale then...

Precise calibration requires distilled water. Effort is likely the reason why they are not popular.

Ah I get it .. you measure both at the same time to reduce measurement error from your scale.