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Homebrewing – Measuring Alcohol Content of Your Beer

One of the first types of tests that most beginning home brewers measure is the alcohol content of their beer. This is an easy test to do, and it is something many people like to know before they start drinking. I find it is one of the first questions anyone asks before they take their first sip of by brew, “How much alcohol is in this stuff?”

Before we go into the methods of measuring alcohol, a little explanation is in order. There are no devices that measure the alcohol directly. The best we can really do is infer the amount of alcohol based on other observable data.

Yeast produces alcohol by metabolizing simple sugars (Dextrose) into two primary by-products: ethanol and carbon dioxide. All the other by-products occur in trace amounts that are irrelevant to our interests here. The carbon dioxide (CO2)is released into the atmosphere, and the alcohol remains.

Because the CO2 has left the liquid, the beer becomes less dense. The more sugar the yeast metabolize, the higher the amount of CO2 that is released, and consequently the higher the percentage of alcohol.

In order to determine the alcohol content of your beer, you need to measure the beer before it ferments, and after it ferments. By determining the difference between these two numbers, you can infer the amount of alcohol in the brew.

There are two ways of doing this measurement. You can measure the density of the beer, or the amount of sugar that is in the solution. We refer to the measurement of the density of the beer as it’s Specific Gravity, and the amount of sugar is expressed in units called Brix.

Specific Gravity

The Specific Gravity of water at 60 degrees Fahrenheit is 1.000. Everything else is either more or less dense than water. You use a simple little tool called a Hydrometer to measure the Specific Gravity of a solution. It is essentially just a glass cylinder with a weight on the bottom and lines showing the different gravity points going up the side. Technically, you are supposed to cool the beer sample down to 60 degrees in order to get an accurate reading. However, as long as the beer is around room temperature, your reading will be reasonably accurate. Just keep in mind; a hydrometer reading of boiling liquid will be way off.

When brewers talk about Specific Gravity they will usually specify either the Original Gravity (OG), or Terminal Gravity (TG). The OG is a measurement of the beer before it ferments, and the TG (also called Final Gravity – FG) is the measurement that is taken after fermentation is complete. The difference between the two tells you how much alcohol is in the brew. As an example, a typical Pale Ale will start off with an OG of around 1.045 and finish off with an TG of around 1.008.

Calculating the percentage of alcohol is as simple as plugging some numbers into the following equation.

% Alcohol = ((1.05 x (OG – TG)) / TG) / 0.79

So, given a few numbers suggested above:

OG = 1.045
TG = 1.008

The equation would look like this:

.0487 = ((1.05 x (1.045 – 1.008))/1.008) / 0.79

So, this beer would be about 4.9% alcohol.

Brix

Another great way to measure alcohol content is by measuring the sugar level. You measure Brix using a nifty little device called a Refractometer. These things are great because all you need is a drop of wort or beer to take a reading, and you don’t have to cool it off before you take a reading or perform mathematical gymnastics to compensate for temperature variances.

There are complex formulas to out there on Internet Land if you want to get super duper accurate, but the simple formula is to just take your Brix level and multiply it by four to get a Specific Gravity.

For our example, let’s assume a Brix reading of 11.25. Therefore we find the Specific Gravity this way:

4 x 11.25(Brix) = 45

So, the “45” in this case means 1.045. In brewing language, “45” actually means 1.045 – which is why this little trick works. You can now take this number and plug it into the formula given above to calculate your alcohol level.

My personal preference is to use the Refractometer instead of the Hydrometer. There is just no way to express the ease of putting a drop of wort on the Refractometer while I’m mashing my grains, or to make sure my gravity is spot on when the wort goes into the fermentor. The alternative of using a Hydrometer is such a pain in the ass that quite frankly I almost never take gravity readings.

On the downside, Refractometers cost much more than Hydrometers. You will pay about $60 – $120 for a Refractometer versus $12 – $25 for a Hydrometer. If you are considering all-grain brewing, then I would highly suggest a Refractometer.

You can get more information on Homebrewing in the Homebrew Section of www.DrunkMansGuide.com

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December 19, 2007 - Posted by | beer, Homebrewing | , , , , ,

37 Comments »

  1. Would it be possible to alter the alcohol content of your brew by maybe starting out with a 30% sugar to 70% water solution before you start making the wort?

    Comment by Nate | April 28, 2008 | Reply

  2. Yes, you can increase the alcohol by adding sugar. However, if I were you I would add the sugar after your mash – not before. If you add the sugar before the mash, then you’ll lose some percentage to the grain. So, you won’t know how much actually made it into the wort.

    Also when you say 30% sugar to water ratio. I’m not sure if you mean by weight or volume, but either way, I would probably lower the additional sugar.

    If your grain bill calls for 10 lbs of grain, then this is roughly equivelant to about 6 pounds of DME. You could add another pound or so of corn sugar to your wort, but any more than that and you will start to taste some negative effects (sour/cidery). Keep the corn sugar below 20% of the total sugar in the wort.

    There is definitely such a thing as too much sugar. Some yeast strains can tolerate a higher sugar (and alcohol) level. A Belgian Wit yeast will ferment a whole lot more sugar than an English Ale yeast.

    That said it is difficult to get your alcohol level above 12% – 14% or so. People do it, but they rarely squeeze much more out of it than that. Most of the additional sugar stays in the beer and makes it overly sweet.

    If you want to push the alcohol level up beyond whatever point your yeast will tolerate, the best way is to add medium quality vodka after your beer has finished fermenting. Vodka is basically pure ethanol and water (corn beer that has been distilled). Other than the ethanol, it is neutral in taste.

    You have to add the liquor after fermentation because otherwise the high alcohol level would kill your yeast before they finish the job.

    Comment by drunkmansguide | April 28, 2008 | Reply

  3. What is the best way to calculate the alcohol percentage if you do not have the Original Gravity?

    Comment by Neil | June 30, 2008 | Reply

  4. Hey Neil, thanks for the question. This comes up for a lot of homebrewers because let’s face it, we’re drinking beer while we’re brewing, and it’s easy to forget to record the OG (or keep a hydrometer in focus for that matter).

    One thing you CAN do is just make an assumption about your OG. If you are brewing from DME or LME, then you know for a fact how much you put in and what your water volume is. So, a simple calculation would give you your OG. Just look up your brand of DME and you can figure it out fairly easily.

    If you are brewing from grain, then that method will not work because of all the many factors involved in mash efficiency.

    If brewing from grain, you can use a Refractometer and a Hydrometer to THEORETICALLY determine the level of alcohol. The following formula is what you would use:

    ABV = [277.8851 – 277.4(SG) + 0.9956(Brix) + 0.00523(Brix2) + 0.000013(Brix3)] x (SG/0.79)

    SG = Specific Gravity (from the hydrometer)
    Brix = Sugar Level (as measured by the refractometer)

    I would tell you that I am not convinced that this formula is very accurate. When I test it against known beer samples, it seems to be off by quite a bit. That said, when I try it, I’m usually drinking beer, so there could be a certain percentage of user error involved.

    Important: Make sure that when you take your readings that you get all the CO2 out first. How? Put the sample in a blender for a bit and really get it flat.

    Also, I didn’t come up with this formula, I ripped it from this site: http://www.byo.com/feature/1132.html. So, if it doesn’t work for you, send your hate mail to them.

    If it does work for you, then I’ll keep the praise.

    Cheers!

    >Matt

    Comment by drunkmansguide | June 30, 2008 | Reply

  5. To clarify: it’s not exactly the CO2 escaping, but yeast changing dissolved sugars (higher SG than pure water) into CO2, which escapes, leaving less dense alcohol dissolved with the water. So the overall density of the mix changes. You measure what you start with, water and sugar, and then what remains and that is alcohol and water. You are correct about the CO2 that might be in suspension, it makes the liquid ‘fluffy’ and less dense. Enjoy the site, thanks for the blog info

    Comment by zymurgy_dude | August 8, 2008 | Reply

  6. I have read the information on determining the aholcol level of the beer I’m making. It is very helpful information. I am making my beer in a product I bought called “The Beer Machine.” Normaly, it takes 5 days to ferment at room tempature and 4 to 5 days to clarify and condition for drinking. The conditioning phase is done in the fridge at a temp. range of 35.F to 38.F. The beer mix comes in a sealed package with a yeat pack inside. You just add 2.6 gallons of distilled water and Brew. Question: I have my 2nd. batch brewing now. I let it ferment and now it is conditioning in the fridge at day 2. How and at what stage could I check the sugar level to imput into the brix formula above? Or, am I just totally off in my thoughts?

    For a look at and discription of the “Beer Machine”, Please go to web site: http://www.beermachine.com. One other note…The mixes come in many different flavors, ale, lager, pilsner. They are Domestic and International Blends, light and dark.

    Here is a list of ingredients in the package of the brew I’m making now which yields 10 liters / 28-12oz. beers.

    The contents are: Powered Dry Malted Extract, Hop Extract and a Brewers Yeast Package. “NO PRESERVATIVES”.

    I AM LOOKING FOR THE SIMPLEST WAY TO MEASURE AND INFLUENCE THE AHCOHOL CONTENT.

    Comment by Richard Lawson | January 6, 2009 | Reply

    • You measure your Starting (Original) Gravity before you put your yeast in.

      You measure your Terminal (final) Gravity after fermentation is complete. Usually, this is after about 2 – 4 weeks for an ale.

      5 Days to ferment??? Not really. That’s just the primary phase. If I were you I wouldn’t put it into the fridge until week 2 or 3. The BeerMachine is oriented around making the beer simple – not really making it the best it can be. I would be patient with it and let it mellow for a while.

      Comment by drunkmansguide | July 15, 2009 | Reply

  7. i had an idea of making home beer with out alc and giving my guests the freedom to add as much alc as they need to their own beer… so i have couple of questions:

    is it possible to avoid using sugar to make alcohol free beer and use sweetener instead. then add alcohol separate later own?…
    how can i add alcohol separately to beer?

    Comment by fidaa | January 26, 2009 | Reply

    • Well, basically it’s difficult for homebrewers to make non-alcoholic beer because most homebrewers carbonate their brew by bottling it before the fermentation process is totally complete. Since it is fermenting, it is going to have alcohol in it.

      If you force carbonate, then you can make non-alcohol brew by simply not fermenting it. However, it doesn’t taste right if you do that. There are chemical changes that take place during fermentation beyond just the production of alcohol. Also, you will have to refrigerate it immediately to hold off the growth of wild yeast and bacteria in the brew that would normally be held back by the alcohol.

      My recommendation is that you brew a low-alcohol brew by using a larger percentage than normal of non-fermentable grains or adjuncts like cara-pils and dextrin. Then you might end up with a beer that has, say, 2-3% alcohol, but it still has the malt taste. Your guests can then add mid-grade vodka to their beer to pop up the alcohol %.

      If you add a couple of shots of vodka to the brew, then it will have the same alcohol content as a high-grav beer, but unfortunately it won’t taste the same. The only way to get the smooth taste of a high-grav beer is to brew it that way and then let it age for several months.

      Comment by drunkmansguide | January 27, 2009 | Reply

  8. Calculating the percentage of alcohol is as simple as plugging some numbers into the following equation.

    % Alcohol = ((1.05 x (OG – TG)) / TG) / 0.79

    Does this formula give % by weight or % by volume?

    Comment by A Herbert | March 16, 2009 | Reply

    • By volume

      Comment by drunkmansguide | July 15, 2009 | Reply

  9. I am brewing a honey heffeweizen that had a starting gravity of about 1.041. I am going to let it completely ferment and then sterilize some fresh blueberries in the form of puree to add to the secondary fermenter. I was wondering mow much will this change my alcohol content. I know that the blueberries will reactivate the yeast and ferment as well, but if I take the final gravity reading in the two weeks following, will I get an accurate reading? I mean from the very starting to the very final after the berries. Or will the addition of the berries midway through mess things up and my final reading be off?

    Comment by Todd | July 15, 2009 | Reply

    • Todd, I’m stumped on this one. One place I would start is to measure the Gravity just before you add your blueberries.

      Next I would apply the “less is more” philosophy to the blueberries and add as little as you can.

      If you measure your grav just before you add the berries, then add the berries and stir it up really well then measure it again you might see a slight difference. If so, then you might be able to get a final gravity measurement with some degree of accuracy.

      But I have to admit I’ve never done this.

      Comment by drunkmansguide | July 15, 2009 | Reply

  10. Is it possible to boost the alcohol content of non-alcoholic beer? Or, could non-alcoholic beer be used to make a batch of beer with an elevated alcohol content by adding yeast and letting it re ferment?

    Comment by Al | August 25, 2009 | Reply

    • I’ve never tried that. But why would you want to do that?

      Comment by drunkmansguide | March 1, 2012 | Reply

  11. Hello!

    This is great advice. You wrote above:

    “If you are brewing from DME or LME, then you know for a fact how much you put in and what your water volume is. So, a simple calculation would give you your OG. Just look up your brand of DME and you can figure it out fairly easily.”

    Could you expand a little bit on what this “simple calculation” is? Sorry if this is a dumb question, but I googled stuff like “calculate alcohol content from LME” and got nothin’.

    Also, all the instructions I’ve seen say to measure the FG at the end of fermentation, but doesn’t the breakdown priming sugar into CO2 to carbonate the bottles also add more alcohol? I’d think I should wait until the beer is fully carbonated (2 weeks or so), and then open one of the bottles and measure its specific gravity to get the real FG. Am I completely off-base here?

    Thanks!

    –Rafi

    Comment by Rafi | September 17, 2009 | Reply

    • Extract has a measurement called “points”. For DME, you’ll see that it is probably around 40 points or so. This means that one pound of DME dissolved into one gallon of water would yield a specific gravity of 1.040.

      The equation is (Points * lbs) / Gallons = Original Gravity

      So, let’s say you have 8 lbs of DME that is rated at 40 points, and you are putting that into 5 gallons of water:

      ( 40 * 8 ) / 5 = 1.064

      If you don’t know how many points your DME is, then just use 40 as a best guestimate. If you’re using LME, then the variance is more, but you could plug in 36 points or so to ballpark it.

      As for priming sugar, the fact is that your alcohol measurements using the kind of hydrometer you probably bought from your homebrew store has such a significant error range that you’ll never notice the difference made by the priming sugar. Additionally, if you are doing it right, then you will actually bottle your beer just prior to fermentation actually completing. So, whether the beer is 5.6% or 5.62% alcohol is the type of difference you’re looking at.

      Now, if you want to be a real beer geek, you can invest in a set of really expensive hydrometers that will get your measurements into the super precise realm that commercial breweries use. In that case, yes, you will want to measure your beer all the time and make spreadsheets of the fermentation curves and all that. This would be fun from a biology standpoint, but it probably won’t get you laid.

      Comment by drunkmansguide | September 17, 2009 | Reply

      • That’s maybe the best answer ever.

        So, since I never measured the SG at any time, I think the next time I open one I’ll use my hydrometer to measure the FG and use your formula (I still have the LME cans around somewhere, so hopefully they’ll have the points somewhere on the label or I’ll just use the default that you suggested). Then I’ll drink the beer, which is of course the point.

        And as far as getting laid, I think I scored major points with my fiancee when we tasted the beer for the first time (this is my very first batch) and she said “hey! this is real beer! I mean, I’d BUY this!” Schwing!

        Thanks again.

        Comment by Rafi | September 17, 2009

  12. Let’s go outside of the box in a hypothetical situation…
    Is alcohol content measured the same in whiskey production?

    Comment by Steve | October 23, 2009 | Reply

  13. The first phase of whiskey production is measured the same as beer. Whiskey is made from a beer-like liquid that is made from corn instead of barley. So, you measure that as a reduction in the amount of sugar in the solution just like with beer.

    Once the beer is distilled. The distilled product comes out of the column at “barrel strength” which is way higher than what you buy in the bottle. At this point the alcohol is measured by specific-gravity using a hydrometer because there is no more extra stuff in the liquid. It’s virtually all just ethanol and water. So, given the specific gravity you can calculate the percentage of each.

    That sits in the barrels for however many years (at least three for bourbon). Then it is watered down to bottle strength – 40% generally – and bottled.

    Comment by drunkmansguide | October 23, 2009 | Reply

  14. Guys, one thing that has been mentioned a couple times on this board is using table sugar to pump up the alcohol in your brew. In case you are interested about why you should only put a small amount in to boost the alcohol, I thought I’d briefly explain what happens with it.

    Table sugar is actually a disaccharide called Sucrose. Sucrose is created by combining one molecule of glucose and one of fructose. Both of these are simple sugars, but since the Sucrose is a disaccharide, your yeast has a difficult time metabolizing it.

    The process of breaking down the Sucrose requires the yeast to produce enzymes, and that’s like work for them. Consequently yeast can convert table sugar to alcohol, but the byproducts of these reactions produces a cidery flavor in the beer. Sometimes a vague hint of the cidery flavor can actually brighten up the beer a bit, but if its too much then it can start to taste weird.

    (Incidentally, our bodies are fueled by the same thing. We break our food down to glucose as well.)

    Comment by drunkmansguide | October 23, 2009 | Reply

  15. Do you have a Refractometer you recommend, and where you recommend to order from?

    Thanks,
    Dan

    Comment by Dan Riley | October 31, 2009 | Reply

  16. I paid extra to get one with a built in light. Now that I have it, I probably wouldn’t pay extra for it if I dropped this one on the floor and had to buy another one. There’s always enough ambient light in the room to take a reading.

    As for where to get it. I think I got mine from morebeer.com.

    Comment by drunkmansguide | October 31, 2009 | Reply

  17. Confused a bit about usage. Your post above sounded like I could use a Refractometer to determine alcohol percentage AFTER fermentation. Maybe I mis-read what you are saying. When I go to the morebeer.com site,
    and click on one of their units,

    http://morebeer.com/view_product/18739//Refractometer

    the info says “They cannot be used after fermentation has taken place as alcohol distorts the reading.”

    My use would be to determine final alcohol percentage. Is this possible?

    Thanks
    Dan

    Comment by Dan Riley | October 31, 2009 | Reply

  18. Agreed. As I said above, when I test known beer samples I’m not convinced that this method is very accurate.

    However, if you are brewing from extract, then you can figure out your starting gravity by using the points formula mentioned above. Then you just do the normal subtraction to determine your alcohol percent.

    Another method you can do is to simply taste the beer. If it still tastes too sweet/malty, then you might need to add some finishing yeast or stir it up a bit and try and wring a little more out of it.

    Comment by drunkmansguide | November 2, 2009 | Reply

  19. On second thought, Dan, perhaps I misread your question.

    Your final gravity can be taken with a hydrometer. Since the beer is room temperature it is already close enough to the proper temp to take a relatively accurate reading.

    For myself, I usually just use the refractometer. It is close enough for government work, but if you want to get super accurate, then you need to cool a sample down to 60 degrees F and measure with a hydrometer.

    For my beer, taste is really the test. If it isn’t dry enough tasting, then I know it needs to ferment longer (or a bit cooler). So, I might put some finishing yeast in and drop the temp a couple degrees and let it hang out like that for a week or two.

    Comment by drunkmansguide | November 2, 2009 | Reply

  20. I have a coopers kit. The beer has been fermenting for 6 days and the hydrometer sinks to the bottom of the tube.

    is the beer ruined or does it just have a higher alcohol content?

    Thanks

    Comment by john | January 24, 2010 | Reply

    • That doesn’t sound correct to me. A hydrometer should never be able to sink to the bottom unless there isn’t enough liquid in the fermentor to float it. I mean, even if you had the world’s worst bacterial infection, the SG shouldn’t be able to go below 1.000 – because that’s water. Unless you are distilling it, the water will stay in there. Ergo – the SG can’t go below that level.

      Comment by drunkmansguide | March 1, 2012 | Reply

  21. Great site and advice.

    Why is it that a policeman can determine my alcohol level
    when I can’t test the strength of something I’m given?

    I would appreciate any pointers on how to get sufficient
    sugars from natural stuff rather than having to buy it.

    Does anybody use freezing rather than distilling?

    Regards

    Comment by Peter | July 31, 2010 | Reply

    • Hmmm, I don’t know how a breathalyzer works, but I do know it’s a different process since it is measuring the level of alcohol vapor on your breath.

      You can get sugars for brewing from just about any vegetation. The question is how to enzymatically break it down to glucose. The benefit to barley is that it already contains those enzymes naturally which is why beer is made out of it.

      Freezing beer is the original form of distillation. It is also referred to as “ice beer”. It won’t have the potency of whiskey, but it will pump up the percentages a bit.

      Comment by drunkmansguide | March 1, 2012 | Reply

  22. In the production of Stout Beer What is the standard temperature range during fermentation?

    Comment by Osuu, Emmanuel Ibiam | November 8, 2010 | Reply

    • 68-70 degrees F

      Comment by drunkmansguide | March 1, 2012 | Reply

  23. This blog has a some of the wonderful information about beer. Kudos guys.
    However, i came a across a video where in a man demonstrates a home made test, to check if beer is adulterated with glycerol.

    Here is the link

    http://www.youtube.com/comment_servlet?all_comments=1&v=UdboD4p10Os

    I wanted to know your comments on this. Is he correct with his claims of beer being adulterated? Is this test valid ?.

    Just curious to know the reason.

    Comment by Karthik | December 21, 2010 | Reply

    • I’m not familiar with this. Perhaps other readers would have better input on it.

      Comment by drunkmansguide | March 1, 2012 | Reply

  24. Hi there, just a wee note that the formula provided technically provides a fraction of alcohol, not percentage. I know, we can all easily enough convert it, but to eliminate any confusion, you might instead multiply the gravity difference (OG-FG) by 105 instead of 1.05. Dividing by 0.0079 would provide the same result, but using the former option reduces potential confusion in number of decimal places to include. Thanks for all the great info!

    Comment by jimmyodonnell | October 5, 2011 | Reply

  25. All I can say is THANK YOU. I’m new to homebrew & math ain’t my strong point. This helps enormously. Happy Brewing!

    Comment by rollospinbot | December 16, 2011 | Reply

  26. […] The beginning specific gravity of my wort was 1.050. I measured three times, just to be sure. And two three weeks later when I finally got around to bottling the brew, it was 1.010. As long as the temperature of the liquid was kept at (about) 60 degrees Fahrenheit (which it probably wasn’t), my final alcohol content was 5.3%. I used a formula found here. […]

    Pingback by Measuring the Alcohol (286th new thing). « laura turning 30 | February 13, 2012 | Reply


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