How to hit Final Gravity target

[elgatovolador]

I’ve been struggling wrapping my head around achieving a specific target final gravity.

The last two batches I did (Pale Ale, same recipe...however one was in my temp controlled mini fridge and the other was just put in a water tub and ice bottles), both ended up reaching different FGs.

Batch 1 (temp controlled)
Post Boil OG: 1.054
FG: 1.008
~ABV: 6.04%
Fermentation time: 5 weeks

Batch 2
Post Boil OG: 1.056
FG: 1.013
~ABV: 5.64%
Fermentation time: 3.5 weeks

Yeast used was WLP001, attenuation 73-80%.

If I would have let Batch 2 ferment for another 2 weeks, would it have reached 1.008?

How does one determine how long to let a batch ferment to reach a desired FG?

If you want a dry finish, do you choose a higher attenuation yeast?

If you want a maltier finish, do you just aim to take fermentation readings around the 3 week mark until you get the wanted result? Or do you just use a low attenuation yeast?

How does one control min and max yeast attenuation? Or is it just a range?

I’m down this rabbit hole because my current beer munchies desire a 5.8% kölsch style and I want it to have a 1.010-1.015 FG to have a sweet/malty tone.

 

[Electricbrew]

Yeast attenuation is a large factor in final gravity, but if you are an all grain brewer mash temperature plays a large roll as well. Mashing at a higher temp will generally leave a higher fg that’s more full bodied and a lower temperature will dry out more.

 

[Jtvann]

Final gravity is when the yeast has finished eating sugars. While you can stop the process early, if you do, you are not at final gravity. This can also be potentially dangerous to do.

When using extracts, as most beginning brewers do, your gravity points are pretty predetermined. All grain brewing has more flexibility in it, though a ton more variables and I wouldn't recommend trying all grain until you have a solid understanding of the brewing process.

You can control final gravity somewhat through yeast selection. Many clean fermenting ale yeasts are similar, with minor differences. Wlp001 vs safale 05 vs San Diego Super yeast for example ... super yeast may fermentation faster and to a lower final gravity.

Dont pick a yeast just because it ferments less though. For example, safeale 04 is very different that 05. Both are ales, and 04 will finish higher. Its is a English ale yeast though which can/will produce fruity esters. That's neither good nor bad, it's just what it does. If you want it, then it's good. If you dont ... then maybe what you want is a clean fermenting yeast, like 05.

I'd suggest to never prematurely stop a beer early from fermenting. If you are bottling your beer, this is very important. When bottling, you need to use a specific amount of sugar to reach the specific carbonation level you want. If the beer is still fermenting and you stop it too early, theres still sugar in the beer than can be eaten. This sugar can add to, in combination any bottling sugar you add, producing higher levels of CO2 than desired. Glass can only handle al much pressure. If you miss calculate, especially if bottling before final gravity, you can create a bottle bomb. This is no joke. That glass can violently explode, embedding broken glass shards into the wall, ceiling, or you.

Keep brewing. You'll learn more with every batch. You might not hit your numbers exactly on every batch. That's ok, it's kinda hard to tell differences in beer with small misses in your numbers. Give the beer time to finish before trying to bottle. The final gravity will be whatever it's going to be. For a particular batch, you cant change it ... that number is locked in. Let it go until it's done, take notes, and try again either the same way or with small adjustments on an identical batch.

To tell exactly when a beer is really done, check the gravity with a hydrometer. When the number is the same for 3 days in a row, it's done. Dont use the airlock as a guide. Airlocks can leak meaning no bubbles that you can see but theres still fermentation there. Airlocks can also release CO2 very slowly that was absorbed during fermentation ... which will mean bubbles that you still see, but fermentation may actually be done even though its bubbling.

Enough with this 10 page essay ... time for a beer.

 

[elgatovolador]

Final gravity is when the yeast has finished eating sugars. While you can stop the process early, if you do, you are not at final gravity. This can also be potentially dangerous to do.

When using extracts, as most beginning brewers do, your gravity points are pretty predetermined. All grain brewing has more flexibility in it, though a ton more variables and I wouldn't recommend trying all grain until you have a solid understanding of the brewing process.

You can control final gravity somewhat through yeast selection. Many clean fermenting ale yeasts are similar, with minor differences. Wlp001 vs safale 05 vs San Diego Super yeast for example ... super yeast may fermentation faster and to a lower final gravity.

Dont pick a yeast just because it ferments less though. For example, safeale 04 is very different that 05. Both are ales, and 04 will finish higher. Its is a English ale yeast though which can/will produce fruity esters. That's neither good nor bad, it's just what it does. If you want it, then it's good. If you dont ... then maybe what you want is a clean fermenting yeast, like 05.

I'd suggest to never prematurely stop a beer early from fermenting. If you are bottling your beer, this is very important. When bottling, you need to use a specific amount of sugar to reach the specific carbonation level you want. If the beer is still fermenting and you stop it too early, theres still sugar in the beer than can be eaten. This sugar can add to, in combination any bottling sugar you add, producing higher levels of CO2 than desired. Glass can only handle al much pressure. If you miss calculate, especially if bottling before final gravity, you can create a bottle bomb. This is no joke. That glass can violently explode, embedding broken glass shards into the wall, ceiling, or you.

Keep brewing. You'll learn more with every batch. You might not hit your numbers exactly on every batch. That's ok, it's kinda hard to tell differences in beer with small misses in your numbers. Give the beer time to finish before trying to bottle. The final gravity will be whatever it's going to be. For a particular batch, you cant change it ... that number is locked in. Let it go until it's done, take notes, and try again either the same way or with small adjustments on an identical batch.

To tell exactly when a beer is really done, check the gravity with a hydrometer. When the number is the same for 3 days in a row, it's done. Dont use the airlock as a guide. Airlocks can leak meaning no bubbles that you can see but theres still fermentation there. Airlocks can also release CO2 very slowly that was absorbed during fermentation ... which will mean bubbles that you still see, but fermentation may actually be done even though its bubbling.

Enough with this 10 page essay ... time for a beer.

Thanks for the safety concerns! I actually gave up on bottling after two batches and moved to kegging.

I’m doing all grain and even though I got the mechanics and basics down I’m trying to understand things more in depth every batch I brew.

 

[elgatovolador]

Yeast attenuation is a large factor in final gravity, but if you are an all grain brewer mash temperature plays a large roll as well. Mashing at a higher temp will generally leave a higher fg that’s more full bodied and a lower temperature will dry out more.

I’ll start digging into mash temperatures then!

 

[elgatovolador]

Follow up question, what would be the FG range that would be considered dry? And what FG would be considered more malty/sweet?

Dry: 1.001-1.005?
Normal: 1.008-1.010?
Malt: 1.010-1.018?

 

[kh54s10]

The only way to get identical FG on 2 batches is to brew 2 beers exactly the same. That means exactly the same ingredients brewed with the exact same procedure. Pitching the exact same yeast. Pitching the exact same amount of yeast that is exactly the same age. Ferment at exactly the same temperature.

In short it is impossible.

FG numbers in a recipe are just a prediction based on calculations. Even seasonal variations of the grains will change the gravity of a particular beer, causing the FG to be different than the prediction.

The yeast will consume the sugars until they are gone or they are chains the particular yeast cannot digest. You really cannot control the attenuation unless you are doing all grain. Then you can somewhat through mash temperatures.

Both of your final gravities seem good, not knowing the recipes.

Time will not make any difference once the yeast chew through the sugars. This is usually finished in 5-7 days. No need to ferment for 5 weeks. I go for 2 weeks. Though longer doesn't hurt anything as long as you have good sanitation.

To determine that you are at FG, wait until all visible signs of fermentation are gone. Wait another couple days for the yeast to clean up fermentation byproducts (this is debated), take a gravity reading, wait a day or two and take another. If there is no change you should be at FG. Stalled fermentations are a slight possibility.

When using liquid yeast I always make a starter. Some don't. That is something that you should research.

Research yeast use and styles appropriate and choose for flavor not attenuation. Though attenuation is part of making a style.

Keep at it. You will learn and you will be making good beer even if you don't get exactly the FG predicted.

 

[Jtvann]

Check out some of the various brewing software options available. I personally beersmith 3. They will give an approximation for final gravity for a given yeast and mash profile.

Generally speaking, the lower mash temp the more fermentable or dry a beer will be. The higher the sweeter.

Longer mash times will lead to more fermentable as well.

 

[bracconiere]

How does one determine how long to let a batch ferment to reach a desired FG?

could try what budweiser does and mix them together...for consistency.

i personally like my beer 8% every time, for calorie reasons, i shoot for 1.060 OG every time and add gluco, finishes dry every time ~1.000, if i want malty, i add more crystal malt, or black patent.....

 

[madscientist451]

my current beer munchies desire a 5.8% kölsch style and I want it to have a 1.010-1.015 FG to have a sweet/malty tone.

For a malty Kolsch, use WLP 029 yeast, Schill Cologne Kolsch malt, and follow one of the many established Kolsch recipes you can find on line.
Here's one that I've brewed a few times and was a hit in the hot days of summer:
https://brewgr.com/recipe/34169/goose-island-summertime-kolsch-kölsch-recipe

 

[501irishred]

The two primary factors are 1) How fermentable the wort is (the type of sugars). 2) the yeasts ability to eat it up (attenuation)

I would highly recommend these videos by Bobby with BrewHardware (owner). There is tons of great information, and he does one of the best jobs I’ve seen breaking down what makes your wort more or less fermentable. Even if you’re not into all grain as yet, it’s very informative.

 

[Bubman]

Here is a link from beercraftr that explains factors affecting OG and how to adjust for FG.

https://www.beercraftr.com/correct-original-gravity/

 

[Alex4mula]

I would care more about SG. Specially for AG. If your process/yeast is correct it should get proper FG. Otherwise you may have a problem somewhere or infection. Just me.