Specific Gravity?!?!

I just started brewing and my first batch of Irish Stout turned out good and gets better everyday! I am currently waiting on a batch of hard cider to be finished, though from what I have been reading it has a ways to go(it's only been 3 weeks).

This whole brewing thing is so cool. There is so much to know and figure out!!!! This is going to get really addicting. So here is a dumb question for starters:

I have tried using the hydrometer and I understand the basic concept behind it, but how do you use it to tell when a brew is done? Is there some magical number that the Final gravity needs to reach?

Also, when someone is making their own recipe how do they know what the OG and FG should be to make a good brew? Is this just guess work or experimentation? I think if I could understand this it would clear up alot!

Lastly, my 4 gallons of Cider started at 1.060 OG any guess on what the FG should be?

Most beer recipes list an expected final gravity. Ciders tend to finish more completely, my apfelwein finished at 0.998 or so unless you stop fermentation early.

Alright, certainly no expert, but here is my take. There is no set Original Gravity or Final Gravity. It depends on your ingredients. I'll assume as a beginner you're brewing extract. If you're brewing a beer that starts with around 6 lbs of LME or DME (liquid or dry malt extract) then you OG will probably be between 1.040 and 1.050. There isn't really a FG to shoot for. The main reason to use your hydrometer for the FG is the figure out when the beer is done fermenting (hence you can rack it to a secondary fermenter or bottle it). When you get the same reading on consecutive days you're good to go. I would guess your FG would be between 1.015 and 1.005. Hope this info helps, but I'm sure someone else will give you a better answer.

To answer your question about recipe estimates for gravity there are standard formulas that are based on the potential gravity points from different types of fermentable items. The surest way to get a handle on this though is to use recipe software like Beersmith or beer calculus. They do the math for you.

Welcome to HBT! Some of the best money spent on brewing may be getting my brewing software (Beer Smith). It figures out a lot for you including estimated SG and FG. You can do the math yourself but for $20, why would you?

My ciders always finish a little below 1.000. Depending on what yeast you use, yours probably will too.

When you make up your own recipe, you can go by the attenuation on the yeast package. The attenuation measures how much it ferments down from the original gravity. For example, say you use a yeast that estimates 70% attenuation. If your OG is 1.045, then you take 45 X .70 = 31.5. Then 45-31.5 = 13.5. Your beer should be done fermenting when you gravity is around 1.0135. Try to use this method to know when you beer is finished because even when following a recipe, your OG can be different from the recipe. Also, make sure you mix the wort with the top-off water very well before taking the OG reading, otherwise you will be off. Not sure you wanted to geek-out that much on brewing, but its necessary.

cmorgan said:

I just started brewing and my first batch of Irish Stout turned out good and gets better everyday!

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Congrats, and welcome to HBT!

This whole brewing thing is so cool. There is so much to know and figure out!!!! This is going to get really addicting. So here is a dumb question for starters:

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There are no dumb questions. At least, at first. After you lurk a while, you'll note that some people - including me - sometimes get testy if someone posts a really basic question without using the Search function. You have not posted one of those questions, so you may live.

I have tried using the hydrometer and I understand the basic concept behind it, but how do you use it to tell when a brew is done? Is there some magical number that the Final gravity needs to reach?

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It's science, laddie. Magic doesn't enter into it. The hydrometer is a scientific instrument that tells you the amount of dissolved sugars in fluid. You use it to tell if the ferment is complete by taking readings over the span of several days. If you observe like readings, the ferment is complete. For example: If you observe 1.010 on Tuesday, Thursday and Saturday, the ferment is complete. If you observe 1.015 on Tuesday, 1.013 on Thursday, and 1.010 on Saturday, the ferment is still ongoing.

Also, when someone is making their own recipe how do they know what the OG and FG should be to make a good brew? Is this just guess work or experimentation? I think if I could understand this it would clear up alot!

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Software will easily tell you what your OG should be. You can purchase standalone software - I use ProMash - or use one of the popular online calculators. Google "beer recipe calculator" and they'll appear. If you like doing sums, you can use a calculator, pencil and paper; you'll need to know the gravity contributions of ingredients, but that's in all the books.

FG is determined by you and your yeast. There is no magic number for FG; some recipes and old books will tell you every recipe should finish at 1.012, and that if it doesn't you think you've screwed up. Nothing is further from the truth. There are dozens of different strains of brewing yeast, and each has distinctive characteristics, including how much they'll ferment. Some are voracious, others lazy. You can learn a lot by brewing five gallons and splitting it into five one-gallon batches, each fermented with a different yeast. FGs will be all over the map, and so will flavors. I encourage you to try it!

Lastly, my 4 gallons of Cider started at 1.060 OG any guess on what the FG should be?

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Depends entirely on what yeast you used. My cider has been sitting at 1.002 for three months, and won't go any further. Others have reported below 1.000. I used an ale yeast in mine; some fellas use cider or wine yeasts. See what I mean about different yeasts yielding different results?

Have fun!

Bob

It's been over a year since I have really been back on this forum and so first I want to apologize for not thanking everyone that answered my question back then... it really helped at the time! Thankfully I have moved much farther beyond this question... I decided after this post that I really just needed to hit the books and read up on my brewing science if I wanted to really get into this whole thing.

A year later I can definitly say I have learned a ton and i am just about to try my first AG brew!!! Also my wife thinks I am a total nerd now... but I guess that just goes with the territory right!

Thanks again!

cmorgan said:

Also my wife thinks I am a total nerd now... but I guess that just goes with the territory right!

Thanks again!

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Here's to all of the "Beer Brewin' Nerds."