Do I Need A Hydrometer For Brewing Beer

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Do I need a hydrometer for brewing beer at home? This is a question I have seen a lot, so thought I would address it. Taking hydrometer readings can sound a little complex, but it really isn’t that difficult.

When home brewing beer it is a useful tool to have, in fact I would say an essential tool to have. But that does depend on how much you want to know about your beer.

Do I Need A Hydrometer For Brewing Beer?

No you don’t actually need a hydrometer for brewing beer, but it is worth using one. Brewing beer without one is like brewing your beer blind. Using a hydrometer will give you the gravity of your wort before it begins fermentation. It will then tell you when your beer has stopped fermentation. Finally it will allow you to calculate the ABV of your finished beer.

Therefore it is not essential to use a hydrometer, but it tells you too much not to use one.

What Is A Hydrometer?

Do I Need A Hydrometer

A hydrometer resembles a thermometer and is used to measure the gravity of a liquid. It all started with Archimedes and his principle of buoyancy, which I am not going into here.

The hydrometer is a glass tube with a bulb like bottom and a thin shaft. The bulb contains material to weight it down and create the buoyancy. On the shaft there is a scale which measures the liquid relative to water.

There are a variety of gravity readings such as the Brix scale and Baume scale. The one that is most used for home brewing is the specific gravity. On the hydrometer this shows a scale of one or zero and three decimal places, with pure water reading 1.000.

Do I Need A Hydrometer For Brewing Beer?

It depends if you want to know what your beer is doing and what strength it is at the end of brewing.

There is no reason not to brew beer without a hydrometer. However it will be a lot more hit and miss, and you won’t know what strength your beer is.

Without a hydrometer you can not know for sure if the fermenting has finished.

If you happen to bottle your beer before it has finished fermenting, then you are probably going to have over carbonated beer. The worse case scenario is your bottles may explode under pressure, which is no joke.

Also without the use of a hydrometer, you will never know the ABV of your beer. It may be way stronger than you think, which could cause some very wobbly legs. It is much better to be able to tell anyone you share your beer with how strong it is.

So, you don’t actually need a hydrometer to brew beer, but it really helps and makes for a more controlled brewing process.

When Should I Take Gravity Readings?

For the purpose of brewing beer we use the hydrometer to take a specific gravity reading before fermentation. Which means the reading is taken before we pitch the yeast. This reading is known as the OG or original gravity reading and should be recorded.

When the fermentation has finished, or we suspect it has finished, then we take another gravity reading and record it. This is known as the FG or final gravity reading.

To determine whether fermentation has finished we take more than one reading. So when we think fermentation has finished we take a gravity reading. The following day take another reading. If the reading is the same as the day before, then fermentation has finished.

A simple calculation between the OG and FG will then give us the ABV of our home brew beer.

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How Do I Use A Hydrometer?

Do I Need A Hydrometer

First of all you will need a white coat, a pair of protective glasses and chemical gloves. Just kidding, none of them are needed. But there are a few things you need, the hydrometer being one of them.

Here is what you need for gravity readings

The beer thief takes the sample of beer from your fermenting vessel, which is transferred to the test jar. The the hydrometer is lowered into the test jar to record a reading.

How To Take A Gravity Reading

Make sure to sanitize your equipment before use, you don’t want to contaminate your beer.

First collect a sample of your beer. The most common way to do this is with a beer thief, however some people prefer to use a turkey baster.

Other methods I have heard are to fill the test jar directly from the fermenter vessel. I don’t see this as good practice, but it is possible I guess.

I have seen some people drop the hydrometer directly into the fermenting vessel. Again it is not something I want to do, but again it probably works.

Second, transfer the sample from your beer thief to the test jar. Fill it with enough beer so the hydrometer can float and doesn’t touch the bottom.

Bubbles around the hydrometer can affect the reading, so most will give it a little spin to clear the bubbles.

Finally once the hydrometer has settled look at the point where the hydrometer meets the beer. This is the reading you want to record and is the OG reading.

Do I Need A Hydrometer

How To Take The Final Gravity Reading

The air lock on your fermenter will give an indication of whether fermenting has finished. During fermentation when the yeast is active, bubbles of co2 will escape through the airlock.

At first this is quite active, but will slow down towards the end of fermentation. When co2 bubbles cease then it is a sign that fermentation has finished.

This is when the hydrometer can tell whether this is true or not. The gravity reading is a repeat process of the OG reading before the yeast was added prior to fermentation.

As I explained earlier a reading should be taken once each day and when the reading is the same two days running means the fermenting has finished. This will then give you your FG reading, again record this to workout your ABV.

How To Workout You Beers ABV

Now that you have an OG reading and an FG reading, the ABV of the beer can be calculated.

The FG reading will be lower than the OG reading and you subtract the FG reading from the OG reading. Then multiply this by 131.25 which will give you the beers ABV.

Lets say the OG reading is 1.043 and the FG reading is 1.007

OG – FG X 131.25

1.043 – 1.007 = 0.036 x 131.25 = 4.725 giving an ABV of 4.7% Vol.

I knew you were going to ask why it is multiplied by the figure 131.25.

It is an equation that includes the density of ethanol and the grams generated per gram of carbon dioxide released. I know I don’t understand it either, but brewers have been using it for years, that’s all we need to know.

Final Thoughts

We now know why it is preferable to make use of a hydrometer when homebrewing beer. Knowing for definite when your beer has finished fermenting is an obvious bonus.

Also knowing the strength of the beer has to be better than not knowing and drinking it blind.

Be careful when using a hydrometer as they are pretty fragile, so easily broken. On the plus side they are cheap to replace if one does get broken.

One thing I forgot to mention is the temperature part of the hydrometer reading. Most hydrometers for brewing work best at 59°F/ 15°C, so make sure your sample is at this temperature.

I checked the sample used in the images for this post with an instant read thermometer. This read 53°F/12°C to begin with. I waited to it read the right temperature before I dropped the hydrometer in.


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