Calculating What to Shoot For (FG)

Hey All,

I am new to this all. Started Feb 15th of this year. Just finished my 5th batch. Just dipping my toe into the brewing scene You have helped me a ton in the past... I have been taking lots of notes from you all as well as on all the steps of my beers.

That leads me to my new question.

Most kits do not give you the FG that you are shooting for. So I went and found this formula: [(OG-FG)/(OG-1)] x 100 = Attenuationto help me.

For my most recent beer... A Belgian Trippel I had an OG of 1.078.
I also found here http://www.homebrewers.com/results.cgis?catalog=&keywords=1338&x=0&y=0 that the attenuation of the yeast is 67%-71%. So I took the middle (69) and plugged it as well as the OG of 1.078 into the formula:

[(1.078-FG)/(.078)] x 100 = 69 and solved to get that FG = 1.024.

Now I would imagine that my FG can vary... so if I end up at 1.026 or 1.022 I would be fine... and that I need to use my hydrometer. But does this seem to be the way I need to go?

Or is there a different/better way to calculate what FG I am shooting for?

Thanks a ton,

Jason

I think that the way that you've done it is fine. It's an accurate measure for apparent attenuation.

It might vary somewhat, but under normal conditions it shouldn't. If it is beyond that range, something isn't normal - stuck fermentation or something causing overattenuation.

Those attenuation numbers given by the yeast mfrs. are just numbers so you can compare yeasts. You might get way more or way less attenuation than that. Your mash schedule will have more influence on your FG than those numbers given by the mfrs.

You just have to get dialed in with your system/process in order to know where your FG should be for a given mash shedule. Taking good notes like you are doing is a great way to get there. But take those attenuation numbers from the mfrs. as just a guideline/range on how it compares to other yeasts, not necessarily what you'll actually get.

Most Tripel recipes call for candi sugar if I'm not mistaken, and that will increase your attenuation quite a bit. As SpanishCastleAle mentioned, the fermentability of your wort will be a bigger factor than your yeast choice.

slowbie said:

Most Tripel recipes call for candi sugar if I'm not mistaken, and that will increase your attenuation quite a bit. As SpanishCastleAle mentioned, the fermentability of your wort will be a bigger factor than your yeast choice.

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So then I should shoot for the lower end of my expected attenuation range?

It depends on your yeast AND recipe what your FG will be.

I'm not sure quite what you mean by "shoot for". Once you have made your recipe and pitched your yeast there is not much you can do to control the FG. For a normal beer, I would wait 2-3 weeks, check the gravity, and then check it again in another week and decide whether or not to bottle. In your case with a higher OG you might want to wait an extra week or so to make the initial gravity check. I don't know a lot about Tripels and whether or how long you would want to bulk age before bottling, but the point is that there are two basic ways to control the fermentability of your wort.

1. Mash temp. The general rule is higher mash temp = higher FG

2. Adding simple sugars. Although I do not know of anyone trying this for sure, I am quite sure that if you used an ale yeast (any ale yeast) to ferment a low gravity mead, you would get attenuation of over 100% This is because the simple sugars in honey are easily fermented by any yeast and would all be fermented, leaving a FG below 1.000 This method is common in IIPAs and Belgian Strong Ales, usually in conjunction with the first method.

The point I'm making is that the only way to control your FG at this point is to add more candi sugar, corn sugar, honey, etc., which, depending on your original recipe, may have a negative effect on your beer's flavor.

Yeast selection will have an effect, but the fermentability of your wort is going to be more important to your FG AFAIK.

slowbie said:

I'm not sure quite what you mean by "shoot for". Once you have made your recipe and pitched your yeast there is not much you can do to control the FG. .

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Yeah... I understand that... I guess by 'shoot for' I mean just so I know if I am way off base. Like if I check after 3 weeks and I am at 1.022 but the FG is theoretically supposed to be around 1.012. I wanted to know if I am at least in the neighboorhood of where I should be.

That is why I was wondering if my method would put me in the right area. I know that your fermentables will have an affect on where I end up... but still... If I know that I should end up at 1.015 and I am making a recipe that uses candy sugar or honey... I will expect to be under that 1.015 I guess.

Again, I am only in this hobby for basically 1 month today.... So I am not sure if I am asking foolish questions or if my comments are offbase.

jalgayer said:

Yeah... I understand that... I guess by 'shoot for' I mean just so I know if I am way off base. Like if I check after 3 weeks and I am at 1.022 but the FG is theoretically supposed to be around 1.012. I wanted to know if I am at least in the neighboorhood of where I should be.

That is why I was wondering if my method would put me in the right area. I know that your fermentables will have an affect on where I end up... but still... If I know that I should end up at 1.015 and I am making a recipe that uses candy sugar or honey... I will expect to be under that 1.015 I guess.

Again, I am only in this hobby for basically 1 month today.... So I am not sure if I am asking foolish questions or if my comments are offbase.

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No, this is a good question, I just wanted to clarify a bit. If you are brewing from kits, most kits that I've seen will give an ABV range, and you can use that along with your OG to estimate a FG ((OG-FG)*131.25)=ABV) OR (FG = OG-(ABV/131.25)). Also, the BJCP style guide at bjcp.org will be helpful if you're brewing to a style. Hope this helps and keep asking questions because it's the best way to learn.

As a first approximation, jalgayer, your method looks fine to me. The apparent attenuation listed by the companies is what you would expect the yeast to do in a normal situation.

If I had two worts that differed only in their OG, one at 1.060 and one at 1.040, with a yeast that had an apparent attenuation of 75%, the former would be expected to finish near 1.015, and the latter around 1.010.

As long as you use your hydrometer to measure what is actually going on, and make sure the reading is stable, then you'll be OK.