If you think this sounds like a cock & bull story I would agree.
I made a Porter at the weekend and tested the OG using my new refractometer against my hydrometer. The reading on my refractometer was 14.25(brix), which when multiplied by 4 agreed with my hydrometer reading of 1057. Now 72 hrs later the refractometer reading is 8.25 which presumably should give an SG of 33. However my hydrometer reading is 20.
I've borrowed my mates refractometer and 2 of his hydrometers and they all agreed with the readings from my own equipment. Have I got this totally wrong? I feel the need for a serious drink!!
A Cock & Bull Story
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mysterio
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Aleman
- It's definitely Lock In Time
- Posts: 6132
- Joined: Sun Jun 03, 2007 11:56 am
- Location: Mashing In Blackpool, Lancashire, UK
Refractometers are no good on fermented/fermenting wort
Well thats not strictly true. What you have to remember is that your refractometer is calibrated to measure the concentration of sucrose in water . . . Maltose is close enough so that it doesn't matter (The actual conversion is 4 times the brix reading less about 4%). When you throw alcohol into the mix that alters the amount the light is bent by as well, making it seem as though there is more sugar in the solution than really is. If you know the SG of the wort there are some complex calculations you can do to convert the 'Apparent' reading to an actual reading (Promash does it for me
)
What this means is that while you cannot measure the current gravity directly you can tell if the gravity is still falling and when it becomes stable. At this point you fill a hydrometer jar, and using your trusty narrow range hydrometer determine the gravity
Well thats not strictly true. What you have to remember is that your refractometer is calibrated to measure the concentration of sucrose in water . . . Maltose is close enough so that it doesn't matter (The actual conversion is 4 times the brix reading less about 4%). When you throw alcohol into the mix that alters the amount the light is bent by as well, making it seem as though there is more sugar in the solution than really is. If you know the SG of the wort there are some complex calculations you can do to convert the 'Apparent' reading to an actual reading (Promash does it for me
)What this means is that while you cannot measure the current gravity directly you can tell if the gravity is still falling and when it becomes stable. At this point you fill a hydrometer jar, and using your trusty narrow range hydrometer determine the gravity
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MARMITE
