Ben Stange on February 18, 2015 7 Comments There are many ways to consistently improve the consistency of your brewing process. Measuring and evaluating the results of a brew day is one of the most important ways you can evaluate your ability to make consistent beer and identify areas in which you can improve your process. Of all of the measurements you can take during the brewing process, one of the easiest and most important to do is measuring the specific gravity of your beer. The specific gravity is used to measure the density of a liquid to infer the contents of that liquid. In beer brewing, we use specific gravity to measure the sugar content of a beer by measuring the specific gravity of the wort or finished beer and comparing it to water. For instance, a specific gravity of 1.000 indicates the liquid has the same density as pure water. A specific gravity of 1.050 is more dense than water by 5%, and a specific gravity of 0.950 would be less dense than water by 5%. Any brewer worth his wort understands that measuring gravity often and well is key to producing consistently high quality beer. Measuring gravity properly will help a brewer do several things: Measure your mash efficiency. Gauge whether you are hitting the targets set for your recipe. Help you understand the balance of your beer and how it can be improved if necessary. Measure the progress of fermentation. Know with certainty when fermentation has stopped or is finished. Calculate the alcohol content of your brew. Hydrometers The most basic tool for measuring the specific gravity of wort is the Hydrometer. A hydrometer functions by displacing liquid based on its own density and measuring the amount of liquid it displaces. If you look at the bottom of a hydrometer, there is typically a wide portion of the body at the bottom and a tapered portion of the body at the top. Inside the bottom of the wider portion is a small amount of metal which functions as a ballast (to keep the hydrometer upright and to weigh it down properly). Along the narrow portion of the body will be a scale that has a prominently marked 1.000 on it. This is the specific gravity of pure water, and all specific gravity measurements are taken in relation to this number. Hydrometers are probably the most basic and least expensive tool for measuring the specific gravity of a liquid, but they do have several drawbacks: Require Adjustments Based on Temperature: They have to be adjusted for temperature. Hydrometers are designed to function at a specific temperature, and variations in the temperature of the liquid require an adjustment to the results. The warmer the liquid, the less dense it will be, affecting your assumptions about sugar content. For best results, follow the instructions which some with your hydrometer. Require Large Sample Sizes: They require large sample sizes. In order to measure specific gravity using a hydrometer, a brewer will usually pull a sample of beer from the fermenter into a graduated cylinder and then discard the sample to prevent contamination. If you measure your gravity several times over the life of your beer, which is a good practice, this will waste several beers’ worth of wort as it ferments. I think we can all agree that this is a bad thing. Click Here to View the Thermometer & Hydrometer Test Kit Risks Batch Contamination: Risk of contamination is increased. Whenever you pop a fermenter open to take a sample, you are increasing the risk of contamination significantly. Some brewers, to get around taking large samples and discarding them, will even simply set their hydrometer in their fermenting wort when they take a measurement, thereby increasing the risk of contaminating the whole batch. Unfortunately, you cannot measure the density without putting a foreign object into your fermenting wort, but you can lower the risk significantly by properly sanitizing equipment and using the right equipment for taking a sample. It requires additional equipment to do correctly. In order to take a sample from a fermenter, you need a thief. In order to measure the results, you need a graduated cylinder. You also need to take the temperature of the wort, so you have to have a thermometer (which you probably already own). The point is that you can’t just have a hydrometer, you also have to have ancillary equipment. Overall, the hydrometer is absolutely a worthwhile investment, and will help you make better beer by measuring your results for repeatability, but it does have several drawbacks. Refractometers Another popular tool for measuring sugar content is the Refractometer. The refractometer does not work by measuring the density of the liquid. It works by measuring the refraction of light through the liquid and calculating the sugar content based on that measurement. There are several advantages to using a refractometer instead of a hydrometer, especially in that the refractometer does not suffer from many of the same shortcomings of the hydrometer. Here are some examples of the advantages of a refractometer: Uses Smaller Sample Sizes: Unlike the hydrometer, the ideal sample size for the refractometer is only a few drops of wort, meaning you can leave more in the fermenter for packaging. Temperature is Less of an Issue: First of all, a small sample size means the sample will cool much faster than a hydrometer sample would. In addition, many refractometers have temperature correction features which will allow for small differences in temperature without inaccuracies. Requires Less Equipment No need for a big, bulky thief and a graduated cylinder or a sanitized thermometer. You can simply sanitize a dropper or a pipette and pull a very small sample. You Don’t Open the Fermenter Much To get a beer or wine thief into a fermenter, you pretty much have to take the entire top off your fermenter. To take a measurement with a pipette, you can simply pull out the airlock, dip the sanitized pipette, and replace the airlock. By reducing the size of the entry point and the time of exposure to open air, you minimize the risk of contamination during sampling. Because you are able to lower the risk of contamination, suddenly you can sample more often during fermentation, and this can help to build a profile of your typical fermentation process and identity problems early on. In addition, because temperature is less of an issue and the sample size necessary to take a reading is smaller, the refractometer allows you to quickly take samples more often during the brew process. For example, you can more easily take your pre-boil gravity and take quick readings during the mash process. The Takeaways For any brewer, a hydrometer can be a valuable tool. For beginning brewers who want to budget their brewing equipment expenses, the purchase of a hydrometer can be easy to justify over the expense of a refractometer. If you are an intermediate or advanced homebrewer, however, the additional one-time expense of the refractometer is well worth the money and will pay dividends in the better consistency of your brewing process and the additional convenience of easier and smaller sampling.