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I've taken my OG at the start, and another reading last night. Only last night did I register that my OG seemed slightly low according to what the brew can suggested as typical. My OG was 1.037 (can said 1.046 was likely) Last nights reading was 1.019 (after 6 days)

My OG was taken at roughly 26C, and last night at a frosty 19C (the fermenting has been very steadily at 20C almost the entire time - yesterday a cold front hit my area :( )

So, should I be adjusting these readings somehow because of the temperature? Oh yeah, using a hydrometer... I guess that's important to know? :)

EDIT: I now see there are calculators to do so, and it seems like the difference in gravity is tiny, from a 7degC variance (which is a fairly big temperature difference, so I'm surprised)

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Do you know the calibration temperature of your hydrometer? It's usually given in the instructions. –  mdma Apr 11 '13 at 11:55
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You could always go the easy way and get a thermohydrometer. –  jsmith Apr 11 '13 at 12:19
    
Unfortunately the hydrometer came in a kit from a local shop, so no instructions... Probably a cheapo hydrometer, all I know is its a Coopers brand... :/ –  baldric Apr 11 '13 at 14:00
    
why the downvote? Is there something I can change in my question to improve? –  baldric Apr 11 '13 at 15:12
    
FWIW, if you used canned extract, and are sure you had the appropriate volume of water, then your gravity is highly unlikely to deviate from the listed gravity of the recipe. Extract doesn't immediately disperse evenly into water, and you can get a stronger/weaker gravity reading if you happened to pull the sample from some area of the wort that wasn't yet evenly distributed. –  Graham Apr 11 '13 at 18:15

2 Answers 2

A 5C difference from calibration temperature variation accounts for about 1.0 gravity point, which can be neglected considering hydrometer precision is 2 points.

A 10C variation account for about 2.0 gravity points.

On the other hand it is a bad idea to not correct let's say up to 5C difference and correct starting from 6C, since this would create some systematic error (1C variation for the same gravity would result in one or two gravity points difference in the measures).

So to be safe correction should be always applied, a variation of 1C or 2C can be still ignored considering you are not in a metrology lab :)

This online calculator supports Fahrenheit and Celsius. And this table shows correction values(using 15C calibration).

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Most hydrometers are calibrated at 60°F (15.56°C). Though the difference will be negligible at your temperatures, you should still use a calculator like this one: http://hbd.org/cgi-bin/recipator/recipator/hydrometer.html

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True for hydrometers in the US maybe, but in Europe it's 20°C. –  mdma Apr 13 '13 at 8:51

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