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I've brewed a good dozen batches of beer from kits, extract, extract+grain, and now all-grain, and I've never measured gravities. Why measure gravity, besides to know what you're getting? Is there any advantage to putting the beer in the secondary as soon as the measured gravity has finalized, instead of just guessing observing that the fermentation is done? Any other reasons?

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  1. If brewing all-grain, taking gravity readings after mashing allows you to calculate your mash efficiency. If your efficiency is low (meaning you're not getting good conversion), you can use this knowledge to pin down problems in your recipe, milling, and mash/sparge processes.

  2. Measuring the gravity before and after fermentation allows you to calculate the amount of alcohol in your beer.

  3. Taking multiple gravity measurements near the end of fermentation allow you to verify that primary fermentation is complete. Airlock activity alone is not enough. This is especially important when bottling as an incomplete primary fermentation greatly increases the risk of bottle bombs.

  4. Using a beer thief and hydrometer makes you feel like a mad scientist and impresses your friends.

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  • @#3-I've had a beer in the carboy for 45 days (Belgian Tripel), the last 14 of which there was no activity. A few days before bottling I bumped the temp up from 72 to 78 and suddenly got another 24+ hours of vigorous activity. Point being, if I hadn't bumped up the temp and just bottled without taking gravity readings, I would've been way over-carbed.
    – Room3
    Commented Dec 1, 2010 at 19:33
  • I would add that if you're brewing all-grain, and you want to make great beer, you need to take readings. I've had mash efficiencies change wildly from one batch to the next, and my bitterness balance would have been way off if I hadn't done a pre-boil gravity reading. Doing the reading pre-boil allowed me to adjust boil times and/or hopping rates to achieve the bitter/sweet balance I was after.
    – Dustin Rasener
    Commented Nov 13, 2011 at 19:15
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I have brewed many batches where I never checked the gravity in the past. You don't really need to check the gravities to make great beer. You do run the risk of not knowing when a beer is complete and maybe having overcarbonation issues in the bottle. But good fermentation practices should, normally, take care of that.

However, I think that when you get past just wanting to make beer to drink and you really want to start nailing down a great recipe; gravity measurements are part of many different data points to collect. Getting those #s help you to hone in on potential issues. And they also help you monitor consistency batch to batch. A solid process in the brew house yields the ability to build better beer because you are consistent.

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  • Agree completely. I've made many great batches without measuring gravity at all. It only became important to me when I wanted to start honing in on my recipes, and when I started brewing all-grain and wanted to make sure I was actually getting decent conversion.
    – Jeff L
    Commented Nov 28, 2010 at 8:43
  • You most certainly do need to check gravity to make GREAT beer, but you can certainly make GOOD beer without doing it.
    – Dustin Rasener
    Commented Nov 13, 2011 at 19:16

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