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AVLbrewing · 02-08-2013, 11:56 AM

Reminds me of a saying I once heard: "A man with one watch knows what time it is, a man with two is never quite sure."

I guess other than doing some two point calibration or buying a third and hoping there is agreement between two of them I'm not sure what else you could do.... Maybe buy a refractometer?

**discokid2k** · 02-10-2013, 03:23 AM

Quote:

Originally Posted by AVLbrewing

Reminds me of a saying I once heard: "A man with one watch knows what time it is, a man with two is never quite sure."

I guess other than doing some two point calibration or buying a third and hoping there is agreement between two of them I'm not sure what else you could do.... Maybe buy a refractometer?

Ha! So true...the refractometer is on my list. I brewed tonight and I had better results doing a few different tricks. 1st, I re-crushed my grain using a bowl and mallet...just to be extra sure. Then I added my full sparge to my mash out to hopefully thin the sugars a little. Also cut nearly 1/2 gal out of calculation just to be sure I wouldn't pull too much water (also added a little over 1qt to cool my mash before starting timer).

Old hydrometer read 1.040 and new read 1.044. Temp correction (@77*) gives me a 1.046 and only -7pts from my expected OG of 1.053. Brewhouse efficiency today rose by 10%, up to an 85%. Not to shabby

**TheZer** · 02-10-2013, 08:08 AM

Quote:

Originally Posted by discokid2k

That is actually not a bad idea. I have tested both hydro's in water and one is spot on, the other is -.04pts. Testing in a solution say, four or five times each and averaging the results is a great test. I will give that a shot.

A 0.04 pt difference in water and a 0.07 difference in wort means the slopes of the two hydrometers are not the same. Take a third reading after adding a teaspoon of sugar to your wort sample, plot the results on a graph, then throw away the hydrometer on the left.

**MichaelBrock** · 02-10-2013, 09:59 PM

Quote:

Originally Posted by BargainFittings

One of the scales is printed wrong. That would be the only way they would be different at start and finish barring user error reading the scale.

I have been thinking about this and I'm not certain that it is true. The variation of buoyancy with density is linear. The relationship between the density of the wort and the vertical movement of the hydrometer is not linear. As the hydrometer sinks further with lower gravity more of the stem is under the surface and so the buoyancy force goes up. Is the diameter of the stem tapered to counter-act this or is the scale non-linear? I have no idea. If it is isn't, then I would expect the hydrometers to be more accurate at higher gravities when less of the stem is under the surface. I tried a two-point calibration which bore this out. Of course it is entirely possible I flubbed something up.