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Beer Chemistry in High School?

While writing this BLOG it donned on me that I would have been much more successful at chemistry in high school if I had learned how to brew beer at that time! Why? Because it is science (which is likely why it didn't make it into the curriculum) but science none the less.

One part of this science involves measurement and this BLOG will focus on the magical tool known as a Hydrometer!

As you work to fine tune your brewing process it will become clear to you that your hydrometer is a very important tool in your belt. Not only can it help you calculate the alcohol content of your brewed beer, it can actually be a great investigation tool for helping you identify proble

ms in your brewing process.

Don't feel bad if you can't tell me exactly what you're measuring with your hydrometer and why it matters so much to the quality and consistency of your beer. You are not alone. If you haven't spent onerous hours researching the topic of brewing, you may only know that you "have to do it because the recipe says so" which is why I'm writing this give you a little more info than you may already have.

First, let's discuss exactly what you're measuring...specific gravity. This is the density of your wort or beer compared to water. Specific gravity refers to the total amount of dissolved solids in water and because we are talking about brewing beer here, those solids are sugar. These are the sugars extracted (actually it is enzymes converting starches into sugars, but for ease of understanding let's just say extracted) from the malt during mashing. The more sugar ​​extracted, the higher the specific gravity reading in your pre-fermented wort and the higher the potential alcohol content in your finished beer.

It's important to note that the fermentation process is essentially the time when your yeast "eats" the sugars present in the wort and creates the much anticipated alcohol (plus CO2 and flavour compounds). But before you pitch your yeast and start that process, it's essential that you take that first specific gravity reading of your wort - called your Original Gravity (OG).

This Original Gravity (OG) is the measurement you take AFTER your boil and BEFORE pitching your yeast and it tells you the potential alcohol content of your beer. This is the point at which you will have the most sugar in your fact if you tasted it right now it would be a super sweet sugar water! Your OG reading should reflect that sweetness by being within a range of 1.030 (light lager style) and 1.080 (or more for imperial ales and barley wines). doesn't guarantee that you will end up with this amount of alcohol because the yeast you use and it's attenuation also play a keys role in that determination...but that will be for another blog :)

To measure your OG, take enough wort to fill your SANITIZED hydrometer tube up to approximately 2" from the top. Remember, you have NOT added your yeast yet. Insert your hydrometer and let it float in the liquid. Spin it gently to help remove any bubbles that may be blocking the reading and wait for it to stop. Each measurement should be corrected for temperature...

Do you remember your high school chemistry class? That's where I learned to "read the bottom of the meniscus" from eye level. The meniscus is the curve in the upper surface of a liquid that in beer is concave in appearance. For a long time and still today, people report reading the bottom of the meniscus when taking a gravity reading but our hydrometer recommends reading it from the top of the meniscus or where the liquid touches the sides of the hydrometer.

Disagree with this method (I did too...seriously I took a lot of chemistry in college)? Do a quick test to confirm it for yourself...fill your hydrometer tube with water and take a reading. The Specific Gravity of water is 1.000. Where do you see your reading (don't forget to correct for temperature)? If you're like me, or Ray Daniels who wrote the book, Designing Great Beers, your 1.000 reading will be in line with the top of the meniscus.

Now that you know how to take the OG reading, record it in your Brew Journal or somewhere you will be able to reference it later.

But... what if the reading you get is LOWER than the recipe called for? Don't worry...this just means your wort is too dilute and you need to concentrate it a little further. This can happen if your actual "brewhouse efficiency" was lower than the recipe anticipated (again...another blog for that discussion).

There are a couple of easy ways to solve this dilemma...

1) continue to boil until you hit your desired OG. Remember you have too much water so evaporating more will concentrate the wort, giving you a higher gravity reading

2) add some light DME (dry malt extract) to hit your desired OG. The amount you add can be calculated using the tool of your choice but Beersmith (my go-to software) has a calculator built in.

Now that you know how to correct a LOW gravity reading, what do you think you do with a HIGHER reading than wanted? The opposite of course...your wort is too concentrated so you need to dilute it with water. Go ahead and add water until you reach your desired OG.


and you notice a low OG, you should "decrease" the brew house efficiency %​ in your brewing software.​​ This will automatically​ ADD grain to​ your recipe to compensate for the lower efficiency ​helping you reach the OG you're looking for.

The opposite is true if your batch ​has a higher OG than​ anticipated...increase your brew house efficiency % in the software and your grain bill will decrease to accommodate that OG.

Now that you have your OG set, it's time to pitch the yeast and wait for fermentation to complete. How will you know when it's complete? You take a FINAL GRAVITY reading.

​The Final Gravity (FG) ​is the measurement taken AFTER active fermentation that confirms both if your fermentation is complete AND if you have achieved the anticipated attenuation (amount of sugar to alcohol conversion expected with the yeast you used).

Why does this matter? Because if you're brewing an IPA with an expected ABV (alcohol by volume) of 6%, you don't want to take it off the yeast when it's only at 4%, leaving residual sweetness in your IPA and losing the character of the style you were brewing. So, if you find your FG is BELOW what is anticipated, leave your beer on the yeast longer because fermentation may not be complete. Take a reading again in a couple of days. When you record three identical readings over the course of a few days, your fermentation is done no matter if you had good attenuation or not and can be taken off the yeast and carbonated (although time for conditioning is always recommended).

Just a note: If you didn't hit your FG dead on, it's really will get better at this over time. If you didn't hit your FG by a long shot, you need to review your mashing process...did you exceed the recommended mash temperatures during that time? If so, you may have converted your starches into UNFERMENTABLE sugars meaning your yeast cannot convert those sugars into alcohol...leaving your beer sweet.

To measure FG, add enough beer to your hydrometer jar to leave 2" from the top. Drop in your hydrometer (actually don't drop might break if it hits the bottom hard) and read the meniscus like described above and write it down in your Brew Journal.

Now it's time to calculate your ABV!!! Use the following simple calculation:

(FG-OG) x 131.25 = ABV%


(1.060 - 1.010) x 131.25 = 6.5% ABV

So have just a little more information than you may have had before on why and how you use the hydrometer that came in your Brew Station. And although it is great to understand these numbers to help perfect your beer, John Palmer, author of "How to Brew", would remind you that your "recipe goal should not be the FG...your goal should be to brew good beer." So go get at it!

Happy Brewing

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