Determining Percent Alcohol

Whenever I've talked to people about homebrewing beer and hand them one of my own, a lot of the time I'll give fair warning if the percent alcohol is above 7% Alcohol by Volume (ABV).  They usually say, "Oh", then wait a second, and finally ask, "How exactly do you know that?".  Most of the time it's someone saying "Really?  You're that much of a nerd that you calculate the percent alchohol of your beer?"  And to them I respond a firm "YES I DO", and I also calculate the percent Alcohol by Weight (ABW), which we'll talk about soon.

In the last post, I wrote about BU:GU ratios and had to briefly explain OG, but I didn't get into very much detail other than to inform you that it tells the homebrewer the concentration of sugar before the yeast is thrown in.  You might wonder how we get such a number as 1.048 for the Original Gravity, and the answer lies in a small homebrewing tool we call a hydrometer (see picture). 

It's basically like a floating thermometer except instead of measuring temperature, it measures the density of a liquid.  To use a hydrometer, you toss it in the liquid and the hydrometer will float to a certain numerical value on the skinny part of it that is flush with the surface of the liquid.  When a well calibrated hydrometer is placed in deionized water at 59 degrees F, it reads 1.000, and this makes sense because the density of water is roughly 1 kilogram per Liter (kg/L) or 1 gram per milliliter (g/mL), they mean the same thing.  When the hydrometer is placed in a solution that contains water mixed with a certain amount of sugar, like the sugars brewers extract from the grains, it will always read higher than 1.000 g/mL because sugar makes the solution denser.  So the OG on the hydrometer for a beer could read a number of ranges from 1.030 (not much sugar) to 1.120 (a hell of a lot of sugar).

You can check the concentration of sugar at any time you wish during the brewing/fermenting process and with the exception of two readings we typically refer to these readings as Specific Gravity or SG readings.  The two exceptions, which are essential to calculating the percent alcohol in your beer are the OG (Original Gravity) and the FG (Final Gravity) readings.  As explained earlier, the OG is the sugar concentration before the yeast is added, and as you can guess, the FG is the sugar concentration after the yeast is done converting the sugar into alcohol.  OG is measured when the wort is cooled and ready for the yeast and the FG is measured just before you bottle the beer.  The time between the two measurements depends on the type of beer, the higher the OG, the longer it takes to reach the FG.  Since you now know those two values I could just give you the formula for calculating %ABV, but where's the fun in that... to the chemistry!

Simplistically, here's what happens to sugar when yeast is added:


C­₆H₁₂O₆ (one glucose sugar molecule) -------> 2 CO₂ (gas) + 2 CH₃CH₂OH (ethanol, *this gets you drunk*)

There's much much more going on when yeast is added, but understand that roughly for every 1 glucose sugar molecule, it yields 2 carbon dioxide molecules and 2 ethanol molecules.  Depending on the type of yeast, most of the time not all the sugar is converted to ethanol and CO₂, which is why some beers can taste sweeter than others.  Let's assume that we just got done fermenting a pale ale and it's ready for bottling, we take a hydrometer reading and record a FG=1.010, and the OG recorded weeks earlier was 1.055.  This may not be the most accurate way to calculate percent alcohol, but let's assume that all of the CO₂ gas produced left out the airlock and all the ethanol produced remained in the beer.  By subtracting the FG from the OG, it tells us the concentration of CO₂ that left.

In our example: 1.055 - 1.010 = 0.045 g/mL CO₂


Since we know the balanced equation for converting sugar to alcohol and gas, we can use stoichiometry (bet you never thought you'd see this again) to determine the concentration of ethanol from the concentration of CO₂ that left the beer.  Looking at a periodic table, we can obtain the molecular weights for ethanol (46.069 g/mol) and CO₂ (44.009 g/mol), and starting with the concentration of CO₂:

Alright, now that we know how much ethanol is in 1 milliliter of our beer and we also know the total weight of everything in 1 milliliter of our beer (from FG=1.010), we can take a ratio of these two values and what you end up with is a percentage of ethanol by weight in the final beer, which is referred to as percent Alcohol by Weight (%ABW):

But the fun doesn't stop there.  If you're from the U.S. like I am you'll notice most breweries report their alcohol percentages as Alcohol by Volume (%ABV).  The difference between ABW and ABV values has to do with ethanol being less dense than water, and because of this the ethanol occupies more volume.  The ABW is basing its value on just the weight of ethanol in say a 12oz bottle of beer, not the space it takes up in the 12oz bottle.  Since the final beer is usually made up of >90% water and some unfermented sugar, that percent of the beer has a density close to water's, which is 1.000 g/mL, telling us that roughly every gram occupies 1 millilers of volume.  Since the other percent has a the density of ethanol we must divide by the density of ethanol to see how much volume it occupies, so every 1 gram of ethanol would actually occupy 1.27 mL of volume.  Here's how percent Alcohol by Volume is calculated:

 

 OR

So our final beer is 5.9% ABV.  If you think about this logically, it falls apart when you get into high percent alcohol beers simply because if you had a 100% ethanol beverage it would be 100% ABW and 127% ABV, which isn't possible.  However, since most beers are within the 2-10% ABW range this method for ABV works quite well.

This can come in handy if you're ever in Europe where they express there percent alcohol by weight, and as an American you might be so used to judging your alcohol intake based on the %ABV that you might make the grave mistake of assuming they're close in value, or worse, the same.  So if you walk into a pub and order a pint that is 5.0% ABW you'll be quick to realize that your beer is actually 6.3% ABV.  If you'd like a quick and dirty way to calculate in your head (because god forbid that you bust out a calculator in a pub), I take a quarter of the %ABW value and add it back to the %ABW:

5.0/4 = 1.25 ---> 5.0 + 1.25 = 6.25% ABV  (I know... sig figs are wrong)

Not exact, but close enough for a quick answer.  Enjoy!

BU:GU Ratio

After reading the book "Designing Great Beers" by Ray Daniels, I've become accustomed to using one of his terms that he introduces called the BU:GU Ratio.  The ratio is a rough calculation, but a quick way to determine how the beer is going to taste before you even taste it (or buy it), and plus, if you drink a lot of craft brews you can impress your friends, so let me lay some knowledge on you.

The BU stands for Bitterness Units.  This is essentially the same number as the IBUs (or International Bitterness Units) of the beer, which most craft breweries print right on the label.  From a homebrewing standpoint, in order have IBUs of a beer you must boil hops.  Any additions of hops after the typical 60min boil result in IBU=0, so boiling them is crucial to beer making.  Most people assume that the IBU number tells you how bitter a beer will taste, but that's not very accurate at all.  The bitterness flavor is also in competition with the malt flavor of the beer, which we learn from the GUs.

The GU stands for Gravity Units.  This number is slightly more difficult to find on labels and if they do print it on the label, they'll print it as the OG, which stands for Original Gravity.  The OG tells us the original concentration of the sugar (in kilograms per liter) just before the yeast is pitched, and it typically looks like this: OG=1.050, which means the original gravity of the beer is 1.050 kg/L.  To convert OG to GU you simply take the non-zero digits from after the decimal.  For example, if OG=1.048 ---> GU=48.  Since the GUs stem from how much sugars we extract from the grains, it gives us a good estimate of how malty a beer will taste.

Now comes the easy part, we simply divide the BU by the GU and we get the BU:GU ratio, which typical values fall between 0.20 and 1.20.  The lower this value, the more malty your beer will taste, and the higher the value, the more bitter it will taste.  I've heard that a nice balance between malty and bitter is with a BU:GU ratio close to 0.50, but it really is a preference to the beer taster, so I'd recommend trying certain beers that you like and make note of the BU:GU ratio.  If the company doesn't print the OG or IBU on the label, you can probably look it up on the brewing company's website, or if that doesn't work, typing the beers name in a search engine works as well.  Trust me, someone will know these values.

Let's do a quick example, a barley wine that has an OG=1.115 and IBU=70:
BU=70
GU=115
BU/GU = 70/115 = 0.61
This tells me it'll have a fairly balanced taste slightly leaning towards a more malty flavor.

Keep in mind, this is nothing but a ratio for individual use, it doesn't really have a definite line separating malt from bitter tastes, so largely it depends on you.  Obviously, there are extreme beers that you'd be crazy not to think tasted like malt or tasted very bitter, but the ratios in between are very subjective.  So have fun with it and use it whenever you can.  Maybe you'll find that no matter what the style of beer you drink you prefer a narrow range of BU:GU ratios.

Source:  "Designing Great Beers" by Ray Daniels

Moose Drool Clone

When my dad came back from a ski trip in Montana he was raving about this one beer that was a local favorite in the area.  They called it "Moose Drool",  and a couple months later I was pleased to find out that Big Sky brewing company started distributing this beer in St. Louis.  As far as brown ales go this is one of my favorites and the specific style, "American Brown Ale", I had not even heard of until this beer came along.

American Brown Ales are described as having a malty, sweet aroma with hints of chocolate, caramel, and/or nutty scents.  The hop aroma can range from low to moderate, typically using American style hops that give the beer a citrusy aroma.  The appearence has a wide range of color going from light to dark brown, clear, and the head ranges from off-white to dark tan.  The flavor consists of nice balance of medium to high malt and hop flavor slightly favoring the malty side.  The aftertaste should be dry with chocolate or caramel flavors as well as and equal balance of the citrusy hop flavor (depending on the amount used).  Mouthfeel should be medium to medium-full body.  Alcohol content is on the lower side ranging from 4.3-6.2% ABV (Alcohol by Volume).

So needless to say, I had an urge to clone this beer.  Unfortunately, I can't say that I came up with this recipe myself, I researched clone recipes and came across one that I thought would work.  I stumbled across a website called Brew365 and I'm pretty impressed with the number of great beers along with their homebrew clone recipes on the site.  If you're looking to brew a clone beer I'd recommend checking them out (listed in the sources).

Moose Drool Clone (Brew365 Recipe)

Grains

9.0 lbs                   Rahr 2-row pale                

1.0 lbs                   Briess Caramel Malt 60L           

0.5 lbs                   Breiss Caramel Malt 20L         

0.5 lbs                   CaraPils Malt                       

0.5 lbs                   Flaked Oats                         

0.33 lbs                 Chocolate Malt                         

0.13 lbs                 Black Patent Malt                    

Hops

1 oz. East Kent Goldings (First Wort Hop)          4.5% AA

1 oz. Liberty (30min)                                           4.3% AA

1 oz. Willamette (5min)                                      4.7% AA

1 oz. Liberty (0min – flameout)                        4.3% AA

Yeast

White Labs English Ale Yeast – WLP002 (Optimum Temp: 66-68F) – 1800mL Starter (Light DME)

Brew Stats                               

Brewed:  11/20/10

H2O/grain ratio:  1.15 qt/lb 

Mash Temp (Time):  155-151F (60min)

Mash Out Temp:  161F

Pre-boil Volume: 6.6 gal

Pre-boil SG:  1.050

Boil Time:  60min

Post Volume Boil: 5.7 gal

Mash Efficiency:  78%

Secondary:  None

Bottled:  12/11/10

OG = 1.060

FG = ?? Forgot to check! (Estimated Range: 1.018-1.022)

IBU = 26.1

BU:GU = 0.44

Apparent Attenuation = 63-70%

ABW(%) =  3.9-4.3%

ABV(%) =  4.9-5.5%

Yeah, so big fail by not checking the FG, it's the first time that's happened!  Oh well, I guess it just teaches us to be more prepared next time.  The estimated range comes from the White Labs yeast website, where they give ranges for percent Attenuation of all their yeast.

A technique we tried for the first time was not transferring to the secondary carboy.  I believe this to be the cause for the hazy appearance of the beer but I can't be certain until our next brew is done.

Overall, I was pretty pleased with the outcome, although after taste testing both the actual Moose Drool and our clone I noticed a few differences.
Appearence:  The actual Moose Drool is very clear when held up to a lamp, but our beer is so dark and cloudy you can hardly see light, even when held directly in front of  a bulb.  Along with that our head was a slightly darker tan, but I'm proud to say that the head retention is roughly same.
Aroma: The clone has a very subtle, barely noticeable chocolate/toasty aroma, whereas the actual Moose Drool has a very noticeable aroma of roasted nuts (and it is delightful).
Taste: I would say the actual Moose Drool has a more full body character when compared to ours, which tasted slightly thinner.  The first taste you notice with both beers is malt, but the finishing taste for the actual Moose Drool is much dryer than ours.  I would say ours has a bit more bitter taste in the end.

Sources:
Brew365
BJCP 2008 Beer Style Guidelines