Multiple FG readings

[davidabcd]

Hello everyone,

Most of the recipes for extract brewing that I've seen (and use) list the OG and the FG. A few list just the OG and ABV%, but the FG could be worked out quickly, even if only by plugging in logical guesses to the formula (OG-FG X 131.25=ABV%).
I go primary three weeks, check the FG and then bottle. I do three weeks because I do and I also can't imagine a full fermentation taking longer.
I see a lot of advice peppered throughout this forum and the UK sister site to check the gravity multiple times; however, that's a lot of fermentor opening. I do understand the purpose of multiple checks but why not just leave the fermentor alone until you know it's done? If someone wants to do one or two weeks and then bottle, why check it more than once if you've hit the recipe's FG?
But to repeat my main question, is taking only one gravity reading at the end safe if it's what the recipe says it's supposed to be? Any reason not to do this?
Thank you.

 

[ancientmariner52]

Hello everyone,

Most of the recipes for extract brewing that I've seen (and use) list the OG and the FG. A few list just the OG and ABV%, but the FG could be worked out quickly, even if only by plugging in logical guesses to the formula (OG-FG X 131.25=ABV%).
I go primary three weeks, check the FG and then bottle. I do three weeks because I do and I also can't imagine a full fermentation taking longer.
I see a lot of advice peppered throughout this forum and the UK sister site to check the gravity multiple times; however, that's a lot of fermentor opening. I do understand the purpose of multiple checks but why not just leave the fermentor alone until you know it's done? If someone wants to do one or two weeks and then bottle, why check it more than once if you've hit the recipe's FG?
But to repeat my main question, is taking only one gravity reading at the end safe if it's what the recipe says it's supposed to be? Any reason not to do this?
Thank you.

The reason for multiple tests is to be certain that fermentation is substantially complete, as indicated by no change in SG between readings taken a few days apart.

You can't assume fermentation is complete simply because you've reached a certain SG. So many variables in brewing, you may finish higher or lower than the recipe's predicted FG.

All that being said, you are probably safe waiting an extra week or two, then bottling or kegging. Folks have been brewing since, what, 12,000BC? Hydrometers are something less than 200 years old, I think.

Your concerns about opening the fermenter multiple times are well founded. I take great care to avoid contamination at those times.