Taking a gravity sample for a hydrometer reading is one of the basic aspects of homebrewing. Without it, it’s pretty hard to figure out the alcohol content of your beer. But you might be surprised how many homebrewers take gravity readings haphazardly.
How do you take a gravity sample without contaminating your beer?
When testing for original gravity…
This part is a little easier because you can take a gravity sample of boiling (sterile) wort, with little risk of contamination.
- Pull a sample of wort at the end of the boil using a clean, glass measuring cup or thief. You’ll need about 3/4 cup of wort for a sample to take your hydrometer reading.
- Place the measuring cup in an ice water bath to cool the sample to 60-70˚F. You can do this while you chill your main batch of wort.
- Pour the gravity sample into your hydrometer testing jar. Give it some time to settle.
- Take the temperature of the sample so you can correct using a hydrometer adjustment calculator, if needed for temperature correction.
- Suspend your hydrometer in the gravity sample and give it a spin. Take your reading. The spin is to release air bubbles that may have attached to the side of the hydrometer. These air bubbles can throw off the hydrometer reading by adding to the hydrometer’s buoyancy.
- If you want, taste the wort, then discard it. While it may be tempting to put the sample back in the wort, this as a great way to contaminate your homebrew. It’s not worth the six ounces or so of beer.
When testing for final gravity…
This part can be a little trickier. Since the wort is at fermentation temperature, it’s much easier for microbes to grab hold and contaminate your homebrew. To take a sanitary sample for your hydrometer reading, you have two options:
- Use a clean and sanitized thief (plastic, glass, stainless steel) to collect a gravity sample of beer from the fermenter.
- Take your hydrometer reading and, if needed, correct for temperature.
- Taste the beer, or discard it. Again, it may be tempting to put the gravity sample back in the fermenter, but this as a great way to contaminate your homebrew.
Option #2: Sample from spigot or siphon
- If pulling a sample from the spigot, sanitize the spout by spraying the inside with a sanitizer solution. Air dry before collecting the sample. If using a siphon, be sure to clean and sanitize it before placing it in the beer.
- Take a gravity sample of beer into your hydrometer testing jar.
- Take your hydrometer reading and correct for temperature if needed.
- Taste the beer or discard it. Don’t put it back in the fermenter!
- If you pulled a sample from the spigot, rinse it out by spraying sanitizer solution into the spout.
What method do you use to take a hydrometer gravity sample?
David Ackley is a beer writer, brewer, and self-described “craft beer crusader.” He holds a General Certificate in Brewing from the Institute of Brewing and Distilling and is founder and editor of the Local Beer Blog.
Using the Thief, can’t you merely dip the sterilizrd tube into the carboy, depress the vavle against the bottom of the carboy (filling the tube and floating the sterilized hydrometer & thermometer), lift the tube to read it, then return the whole thing to the carboy?
Kilocharlie, yes The Thief will work very well for this purpose — just as you have described. We have a very similar product that is used the same way:
Thank you – I see you just depress the valve against the side of the carboy. I guess you could have named it "the Spy" instead of the "thief" or the "sampler".