Ask Mr. Wizard

High OG Measurements


George Boras • Niantic, Connecticut asks,

I’ve recently brewed 10 gallons (38 L) of an imperial IPA. I fully expected a high gravity beer, but I didn’t know how high. When I went to take my OG, it was out of the readable range (up to 1.080) of my hydrometer. In the future, what would be the best thing for me to use to be able to get my OG? I’m not very familiar with refractometers (and I do not own one) and was wondering if this would be a worthwhile investment


The easy thing to do here is to stick to lower gravity beers and you won’t have to address this problem. But if you are like most homebrewers and craft brewers who don’t find my humor funny, then my suggestion would be to purchase another hydrometer. Since hydrometers operate on a linear scale, the delineations of the scale are related to the range of the scale, for example 1.000 to 1.080, and the length of the hydrometer. You could have a short hydrometer with a wide range, but it would be difficult to read. Generally, longer hydrometers with smaller ranges are more accurate.

Most commercial brewers have hydrometer sets that cover the range of specific gravities encountered in the typical brewery. One common set has three hydrometers with ranges of 0–8 °Plato (~1.000–1.032 SG), 8–16 °Plato (~1.032–1.064 SG) and 16–24 °Plato (~1.064–1.096 SG). This covers the range from first wort collection through finished beer and the hydrometers are long enough to give an easy to read spindle with 0.1 °Plato resolution. I suggest asking your local homebrew supplier if they offer a range of hydrometers and if they do, then buy another hydrometer or two.

I like hydrometers because they are relatively inexpensive, durable when treated with respect and they do not require recalibration. They also measure density and that is the language of brewing. Refractometers work well for wort, but once fermentation begins alcohol affects light refraction and the data collected from a refractometer is not comparable to data collected from hydrometers. Personally, I do not believe a refractometer is a good investment for most brewers.

Another thing you could do is dilute your wort sample using volumetric flasks so that you have a true volumetric dilution. The math is not straightforward and you need to use an extract table. I won’t clutter this answer with details because most brewers will probably not use this method. If you want to do this you perform a dilution and calculate the weight of extract in your sample after measuring the specific gravity or °Plato (both values are required for the calculation and if you know one you can calculate the other). Weight of extract equals specific gravity x °Plato x liters. If you know how much extract is in a diluted sample, then you can use a table to determine the specific gravity of your undiluted sample. At Springfield Brewing Company we routinely dilute wort after boiling with water to adjust specific gravity. Usually we dilute the wort by 1–2 °Plato. In order to do this we measure wort density and wort volume and do some simple number crunching with the aid of extract tables to accurately calculate dilution water volume.

Of course the other option is to simply know that you have strong wort and to not sweat the details of knowing exact specific gravity. Happy brewing!

Response by Ashton Lewis.