Hydrometer or Refractometer

I was just wondering what peoples experiences have been with refractometers. Worth the price?

I recently purchased a refractometer (from northern brewer) so that I can take more readings and use less beer, but I have found that it contradicts my hydrometer. My current beer reads 1.030 on the Hydrometer but on the refractometer is showing 12 % brix (no matter how many times I retry the sample). My understanding is that 12 brix is the same as 1.0485.

I have checked the hydrometer reading from two independent hdryometers, so I don't think thats broken.

Anyone have an idea what is going on? Is my refractomter broken? Am I using it incorrectly?

Thanks

The refractometer doesn't actually measure the gravity (or density) of the beer. It measures the refractive index (how much light is bent when passing through it). Before you start fermenting, the amount of light bending and gravity are directly proportional to the amount of sugars present. Because of this, you can convert one to the other using a simple formula.
When you start fermenting, you produce alcohol by converting the sugars. This causes a reduction in gravity because sugars are heavier than water, while alcohol is lighter; but only has a minor effect on the refractive index as alcohol has a similar affect on the refractive index as sugars. As you use up the sugars, (lowering the refractive index) you produce alcohol (raising the refractive index)
The refractometer is therefore pretty much useless once fermentation has started, but they are great for determining (indirectly) the original gravity.

I hope this makes sense.

-a.

Yep that makes tons of sense.

What about promashes conversion for refrectometer readings during fermentation? Do you consider it to be accurate (i.e. can I rely on it, or should I just stick with my hydrometer)?

My guess is that it can adjust based on the amount of alchohol in the sample, assumming you have your OG.

Thanks

You can make adjustments, but they really have two different jobs. The refrectometer shines for checking the wort coming out of the mash or any time before fermenting. The hydrometer is best for verifying the fermentation is done.

I just checked Promash, and played with a few figures (both Gravity and Plato).
The gravity figures are interpreted as I would expect, but the Plato figures seem to assume that the only thing to be considered is the amount of sugar in the sample. i.e. it seems to ignore the effect of alcohol.
I assume that it may be possible to use Promash if the sample is heated enough to evaporate the alcohol before taking a reading, but I don't make any guarantees.
You could check out http://byo.com/feature/1132.html which explains how to calculate ABV, but it made my brain hurt. I just use mine for monitoring the sparge, and getting pre-fermentation gravities (but I may try boiling off the alcohol and comparing the results against the hydrometer).

-a.