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Old 03-18-2009, 11:46 AM   #1
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Default Reading a hydrometer - confused

What's the correct way to read a hydrometer?

This website - Stevenson Reeves - How to use a hydrometer - says:

The correct scale reading is that corresponding to the plane of intersection of the horizontal liquid surface and the stem. This is not the point where the surface of the liquid actually touches the hydrometer stem. Take the reading by viewing the scale through the liquid, and adjusting your line of sight until it is in the plane of the horizontal liquid surface. Do not take a reading if the hydrometer is touching the side of the hydrometer jar.

And they have this image to illustrate:



The instructions that came with my hydrometer tell me different, however. From the picture above, they say the reading should be 980 - ie, where the surface of the liquid touches the stem, not the intersection of the horizontal liquid surface. This contradicts everything I've read on the internet

Also, the hydrometer jar/tube is quite thin and the hydrometer always slightly touches the edge.

My beer is now at 1007 or 1006 depending on which point I should take. Bottling should occur at 1006 or less. The kit advises 4-7 days and it has been six days. Should I wait another day or is it ready?

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Old 03-18-2009, 11:58 AM   #2
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Start here http://www.homebrewtalk.com/f14/hydr...lenged-108960/
then do a search if that doesn't answer your questions. lot's of info on how to read them

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Old 03-18-2009, 12:12 PM   #3
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I sterilise my hydrometer and drop it in the bucket. Then I compensate for the water tension directly around the hydrometer.

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Old 03-18-2009, 12:20 PM   #4
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Make sure that your test tube is as vertical as you can get it, and put your sample+hydrometer into that. The meniscus is the "collar" or bent up liquid around the edges of the tube, and around the hydrometer on the surface. It is caused by surface tension in the liquid. Your illustration shown above is correct - don't measure where the liquid curves up to touch the instrument, instead try to see where the sample is flat and try to figure out where that level of liquid would bisect the instrument's graduation marks.

If your hydrometer is different and calibrated to the meniscus instead of how all others are calibrated, fill the tube with ~70F (or whatever temp is says it is calibrated to) distilled water and re-measure. If all is well, it should be exactly 1.000.

Grab a couple or 3 sanitized turkey baster's full, put them in your test tube (usually the tube the hydrometer comes in works great), put in the hydrometer, spin the instrument to fleck off bubbles, and do the stuff above. Drink up the sample when finished.

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Old 03-18-2009, 12:29 PM   #5
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There is conflicting information out there regarding how to read the meniscus. The instructions with my hydrometer say to read the upper part of the meniscus. Maybe it just depends on the calibration of the hydrometer when it was manufactured.

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Old 03-18-2009, 12:54 PM   #6
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There is a standard "proper" technique to read a hydrometer in use by the scientific community. However, they are probably not using the $0.47 "Made Somewhere Overseas POS" that we commonly encounter in homebrewing. For this reason, instructions differ from the norm.
As nebben stated, the best recourse would be to take a reading with YOUR hydrometer in distilled water at it's calibration temp and see where you should read YOUR hydrometer...... On the meniscus or level with the surface of the liquid.

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