Properly using refractometer

[TeufelBrew]

All excited, my new refractometer arrived in the mail!!:D Now I can measure wort right out of the lauter stream without cooling it off.!

Took sample of tap water and it showed 0% brix. Fine there. Took sample of fermenting beer and measured SG with hydrometer. Down to 1.012 right in line with what I expected. Stole a sample from that and put in my new refractometer. I expected to see 4% brix. It was at 7%?!?! Isn't that roughly equivalent to 1.028?

Do I need to calibrate with distilled water and then check against known hydrometer reading? The refractometer is ATC type and measures up to 32%brix. I let all samples cool to temp of device (at least 30 sec.)

[hooky]

I believe without knowing your starting point and doing some math, a refractometer is worthless once your fermentation is underway.

Here's spreadsheet from morebeer.com to help with the math part.

[beerking]

Hooky is right, although I am not familiar with the spreadsheet, the source is good.
Basically, it "boils down" to this (pun intended):
The refractometer you have is design to measure sugar in pure water. Some minor impurities are no big deal, but once your wort has done any significant fermentation, the alcohol in the solution will throw the readings off significantly. The spreadsheet provided should take the amount of alcohol into account (which is why initial gravity is important) and calculate the adjustment for you.

[TeufelBrew]

Thanks guys! I was so worried (I know RDWHAHB!) about my new toy not working I didn't think it through all the way. I know that ProMash lets you enter either Hydrometer or Refractometer readings so I just ran with it. I really am working on the patience part!!! I have let my Weizenbock bottle condition for 2.5 weeks and haven't sampled it once! May break down tonight though.....

[beerking]

I have let my Weizenbock bottle condition for 2.5 weeks and haven't sampled it once! May break down tonight though.....

It is definitely time for that first bottle!

[TeufelBrew]

Hooky, Thanks! Now that brain is plugged in, I checked against OG and it came out .001 different than my hydrometer reading. I'll take operator error (aka variance) if it stays in that range. Much obliged for the sanity maintanence!

[hooky]

sweet. glad it helped you out.