Brew Dudes

Homebrewing blog and resource

Gravity Readings During Fermentation

The only way to know that fermentation is complete is to take a gravity reading from your fermentor.

Here are points to keep in mind about gravity readings during fermentation from my perspective:

  1. You want to get a long, thin cylinder/tube of some sort that is easy to clean and sanitize.  I have seen homebrewers use (new) turkey basters.  I have seen homebrewers use glass wine thieves.  I have a nice plastic one that can be broken apart into 3 pieces for easy cleaning.  Whatever you use, you want to make sure it fits the opening of your fermentor and it has openings on both ends.
  2. Like I alluded to earlier, clean your tube well and sanitize it before you use it to take your gravity reading.  It is extremely important that you are confident that your tube is cleaned and sanitized (TWSS).
  3. Open your fermentor in a non-drafty place. You want to minimize the chance that wild yeast get into your fermentor.
  4. Put the tube into your fermentor to a level that fills the tube with a good sized sample.
  5. Put your thumb on the end of the tube that is in your hand and slowly pull the tube out of your fermentor.
  6. Use the sample for whatever tool you use to get gravity reading like a hydrometer or a refractometer. If you are using a hydrometer, you may need to repeat the process to get a sample big enough for a reading.
  7. Some brewers return the unused part of the sample back to the fermentor.  If you think it is clean, then go ahead.  If you feel like you have compromised it in a way that may bring infection or other bad things to your beer, just chuck it or drink it. For instance, if you didn’t clean your hydrometer cylinder, don’t put sample back in the fermentor.

If you have hit your target final gravity, then go to your next stage of the beer’s life.  I use samples from the primary fermentor for a few purposes.  One is to check the gravity.  The other, if I am brewing a lager, is to taste it for diacetyl and see if I need a diacetyl rest to have the yeast clean it up.

Hey, while you’re here… read some other blog posts that are related and you might find helpful:

Kegging Your Homebrew

Cask Conditioned Homebrew


Switching Local Home Brew Shops


Maibock Gravity Reading


  1. I like to setup a “mini fermeter” to check my gravity. That way I have no risk of infection and I also know exactly what is going on in the full scale version. Check out my post on it here:

  2. JW

    Honestly, I also don’t do mid-fermentation gravity checks – its just too much of a pain and you’ll lose about 1/3 to 1/4 a bottle beer each time you do it with a hydrometer. Using a refractometer is the way to go, although it is not straight forward once fermentation starts (i.e. the alcohol in solution will throw off the refractometer reading – the more alcohol, the more trouble it gives the measurement).

    One resource I remember hearing about is the site. They hace posted at least one video on using a refract during fermentation, as well as developing a spreadsheet that will allow you to take SG measurements during the ferment (it mathmatically removes alcohol’s effect on the EG meadure).
    Good luck!


  3. Roel

    For a nice (javascript-driven) page to calculate alcohol from OG and Brix, try . If you’re brave, look at the page source for their calculations.

    I use a refractometer that strongly resembles the one Morebeer sells, and is ubiquitous at Ebay shops. Using it is a breeze, but the contrast of the reading scale is highly dependent on the clearness of the fluid you’re testing- and Bacchus knows beer isn’t necessarily clear.

  4. Sorry, I know this post is a bit old.
    One thing that’s worked for me in the past is to just keep a hydrometer floating in the wort for the entire fermentation. It can be a little tricky to read with the krausen and the diffraction in the sides of the carboy, but you don’t lose anything or risk contamination, and you can take as many measurements as you want.

  5. evan

    if i’m using a bucket with a spigot, is there a reason not to take a sample through the spigot rather than opening the top?

  6. Evan – nope. If you have had luck fermenting in a bucket with a spigot, then you should be able to open up the spigot to get a sample for a hydrometer reading.

    Although I haven’t tested it, I am not confident that my bottling bucket is airtight enough for fermentation.

  7. Dave

    How do you take a sample through the spigot without taking in a bunch of dead yeast and other sediment sitting at the bottom of your bucket? You surely go through a lot of beer trying to get a good one. I don’t even know it is possible.

  8. Good question Dave. I think the sediment layer would make getting a good sample out of the fermentor really tough.

  9. Roan

    Dave if you have a spigot, you will need a sediment reducer. it helps to keep the yeast in the bucket and out of the bottle.

  10. Dave L

    I have a plastic primary fermintation vessel and I intend to keep my beer in there for two weeks. What is the significance of the bubbling coming out into the airlock? For the first couple of days it was really bubbling away. Now, it’s maybe a bubble a minute or two. Is this normal, or should it still be bubbling like it did the first couple of days?

  11. Yes it is normal. The airlock bubbling will decrease as time goes on. Towards the end of the two week period, it may slow even more…but this is ok.

  12. Luciano

    “If you have hit your target final gravity” isn’t a risk ans so assume that all sugar in the wort was really consumed ? Shouldn’t you expect one or two days to assure that the final gravity has stabilized ?

  13. Hi Luciano – if signs of fermentation have ceased and your final gravity has been met, I don’t think you need to wait for any stabilization. In my experience, I have never had any issues with the final gravity going down any lower.

  14. Della

    Sorry, i am really new at this and … French … so the’re is so many terms and words i don’t understand . So my question is.. What is the reading i want to see to actually know when i Hit the target final gravity ????? i see no numbers on my hydrometer ! what is the measure i need ? one inch of brew on top of collected beer ? what am i looking for exactly ?

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