In brewing, there is no tool more important to the brewer than some device to determine the sugar content of your beer wort. Not only this, but it is also a simple way to determine the alcohol content of your beer as well once fermentation is done. The hydrometer is truly the indispensable tool in the Brewmaster’s Tool Chest. To some people, it may seem obvious that you need one of these, but truth be told, you don’t really “need” it to make beer. Heck, even the first few batches of beer I made from kits, I didn’t end up using a hydrometer. It was really more of an afterthought, but I certainly couldn’t tell you what the alcohol level was in my beer.
It does seem kind of odd that I say it is indispensable, yet say you don’t need it. You can still make beer without it. Pitch yeast and away you go. But like any tool, it is about information, and what that information can do for you. Never before could one simple tool tell you so much about what you are doing that it must be indispensable, especially when you are doing all grain. Lets break down the brewing process.
We weigh out our grains to try and match a certain beer style including alcohol content. Well, if you have all your grain specs, you might have a dry extract CG (course grain) of 80%, which would give you a theoretical yield of 37 (out of 46) gravity points per gallon per pound of malt used. This means that if you were going to use 10 lbs of base malt for a 5 gallon batch, quick math in the head would dictate that at 2 lbs of malt per gallon, you would have an original gravity of 1.074.
Great, now we have a high alcohol beer, this is going to be great! But wait, you finish your beer fermentation and it still takes 3 pints to get a decent buzz instead of 2. Dummy! You forgot to measure what your actual original gravity was. For that, you need a hydrometer. So lets do that batch again. 10 lbs for 5 gallons. We do our mash, then boil to 5 gallons and measure our gravity again and realize that we didn’t get 1.074, we got something around 1.054. Nearly 20 points off the estimated mark.
This is where being able to measure your gravity can actually tell you what your brewhouse efficiency is. You know that mathematically, based on the malt analysis, you should have 1.074 but got 1.054. By simple math, 54 / 74 = 72.9% efficiency. So you need to look back at what you are doing in your mash to be able to bring that number higher. I personally get about 74% to 76% brewhouse efficiency, but on a homebrew scale, the cost of additional malts to meet my original gravity estimate is only about $1. Professional breweries can get 82% to 92% efficiency.
Without a hydrometer to take these kinds of measurements, you are going in blind and know nothing about what your brewhouse is doing for you, other than that it is converting starches into sugars. How much of those sugars you are getting will be unknown.
The next process once you are done with brewing your wort is actually fermenting it into beer. I’m guessing that if you don’t have a hydrometer, you are probably going to judge whether your beer is done fermenting or not by airlock activity. It’s a great quick and dirty way to tell if the yeast are slowing down, but it won’t tell you that fermentation is done. Heck, there might be more to it than your yeast. What if you have wild yeast drying out your beer and you don’t know it? There are ways to stop fermentation using either cold temps or sodium metabisulfite in an emergency.
Airlock activity is a great way to see if the yeast is highly active. It is also a way to see if your beer is degassing as well. The only way to really tell when fermentation is done is by taking hydrometer readings periodically. You will also discover whether you have a stuck fermentation this way as well.
Let’s say we are looking at that 1.054 OG beer that we just imagined we brewed. We used a yeast strain that at proper pitching rates and a decent medium to light body mash temp should get us down to 1.010 to 1.012. It is easy enough to see hyper yeast activity in those early stages, but once it settles, the yeast may still be slowly working away around 1.020 or slightly lower. Best way to tell if your beer is done fermenting is to take hydrometer readings periodically. If you have readings that are identical when a few days apart, your fermentation is probably done.
Likewise, if you were targeting 1.010 as a minimum and your gravity is dropping below that, review your equipment and sanitation procedures because there is a chance of wild yeast infection. They enjoy complex sugars and will dry the beer out quite substantially. Best bet is to halt fermentation. Sodium metabisulfite will kill yeast in the beer. It is safe to use as it can also be used to get rid of chlorine in tap water. Without the hydrometer reading, taking a step like this would probably not have crossed your mind.
I did mention stuck fermentations earlier. Let’s say that the 1.054 beer we brewed stalled at 1.023 or something like that for a few days. Fermentation is probably not done, but the yeast aren’t working. Why? Chances are you may not have pitched enough yeast. Maybe even pitched stressed or unhealthy yeast and it doesn’t feel like working for you. Maybe you inadvertently mashed your beer at too high of a temperature and extracted too much complex sugars for your yeast to handle. Either way, using the hydrometer to determine what is going on is the first step to really solving what problems you may have.
Finally, and this happens to be the main reason most people use a hydrometer, determining the alcohol content of your beer. This one is easy enough with a gravity calculator. You need your original and final gravity. If you want to do it by paper, well, here is a formula for you to get you what you need: ((OG – FG) * 105) * 1.25 = Alcohol by volume. In our case, ((1.054 – 1.010) * 105) * 1.25 = 5.775, or for the sake of simplicity, 5.8% ABV.
Lastly, don’t forget that hydrometer readings are temperature sensitive. Most hydrometers are calibrated to about 60 degrees Fahrenheit. If the temp is higher, the gravity will under read. If the temp is lower, it will over read. It isn’t as critical if you are fermenting around 65 to 70F as you may only be one point off, but when you are determining your original gravity after your boil, and your wort is still hot, account for it because at near boiling temperatures, the hydrometer will under read by up to 40 points. I find when I’m checking pre-boil gravities, at around 150F (post mash), gravities will be nearly 15 points out. By not calculating for temps, chances are you may thing you are drinking a 5% ABV beer, but realistically, it is closer to 7%.
Like I said earlier, the hydrometer is an indispensable tool, but you don’t need it. If you are a true hobbyist, or a professional brewer, that simple little instrument can give you key bits of information to tell you more about your beer and equipment than you might have originally though. Don’t just think of the hydrometer as a way to measure alcohol. While ultimately, that is what it is primary use will be, it will help you start troubleshooting nearly all of your major brewing issues.