Stuff I Sort of Know About: There is No Way Around Needing a Hydrometer

by V Rose Dahrke

Today’s topic: mead making. Sort of. What I have to say is applicable to all newish home-brewers, whether they be making mead, wine, or beer. It goes like this: you need a hydrometer to do these things properly. They are like $8 at most places, and most experienced brewers will tell you to buy a handful because they are delicate glass instruments that tend to roll off counters like lemmings off cliffs. I haven’t broken mine yet, but I’ve only had it for two and a half batches and I’m terribly fussy about these things. I take no responsibility for anyone else’s lack of OCD.

I swear to you, this was the least blurry picture I could manage. Scaled in Brix, Spec. Grav., and Potential ABV.

Da-fuq is it?

It’s time for science, that’s what it is. All forms of brewing are about doing one thing and one thing only: turning sugar into alcohol. Sugar comes from many places—fructose from grapes, fructose and glucose from honey, all possible -oses from malt—but the intent is to make it all end up as alcohol via fermentation. Quite simply, a hydrometer is a floating glass tube which tells you how much of your sugar has completed the process by measuring the density of the liquid (“wort” if it is malt, hops, and water becoming beer and “must” if it is honey or fruit and water becoming mead or wine).

Sugar is denser than water.

Water is denser than alcohol.

If I drop a hydrometer in a mixture which has a lot of alcohol in it, it will sink lower than if I drop it in a sugar-heavy mixture. The more alcoholic a mixture is, the less dense it is, i.e. the less there is to hold the tube up. Got it?

Got it. Why do I need one?

Hydrometer measurements (technically measurements of “specific gravity”, which is science-talk for “how much heavy stuff is in my drink”) are about the same two things as Independence Day: getting as drunk as possible and trying not to blow your hands off. These are both admirable goals and, if you plan on making a habitual practice of brewing your own booze, they should be your primary two goals. Otherwise a) why are you even doing this and b) it’s hard to drink with no hands.

1. Specific gravity measurements are used to figure out how much alcohol by volume your final product contains. You measure the specific gravity of the initial must and the final gravity of the finished mead, convert both numbers to potential alcohol using the chart the manufacturer helpfully includes with the hydrometer, and subtract the final from the original. BASIC MATH, DO NOT BE FRIGHTENED. This tells you how much more alcohol has been introduced by the fermentation which—unless you’re doing things terrifyingly wrong—should be all of it. Trust me, the question “Is this a 5% abv bottle of beer, or a 9% abv bottle?” is not a negligible one, especially if you plan of giving your produce to friends and family. You need to know.

2. Proper use of a hydrometer is the only way to be absolutely certain fermentation has stopped. If several successive measurements over a period of AT LEAST a week read the same, it’s done. Lack of bubbles in either the must or the airlock is a symptom, but not proof. It has to be done before you bottle, or introduce a little more sugar as “primer” to make it bubbly. If it isn’t done and you were intending to make a “still”—that is, non-bubbly—wine AND you get reasonably lucky, you will end up with a sparkling wine. Fermentation will continue in the bottles, creating a slight build up of carbon dioxide which will manifest as bubbles. Basically, you will do accidentally what priming is meant to do intentionally.

If you aren’t lucky, you’ll have what’s called a bottle bomb. Your sugars had substantially more fermentation to go, or only had a little left and you primed the bottles. Priming uses reasonably precise amount of sugar to achieve the desired carbonation, and if the initial fermentation hadn’t stopped, none of your sugar measurements were right. Over time the continued fermentation will create a massive build up of carbon dioxide, resulting in explosion. I’m not talking “shook a soda bottle and opened it” explosion. I’m talking anywhere from “shatters in your hands when you try to open it” to “frag grenade made of glass”. Remember, a five gallon batch of wine or mead produces about 25 bottles, and a batch of beer the same size about 54. You probably stored them all in the same place, didn’t you? And they’re all fermenting at roughly the same rate…

Oh, the humanity.

I store my mead—especially stock made before I bought a hydrometer—carefully, in a cabinet in a stone alcove in the crawlspace in my basement. Nonetheless, if my entire stock (35+ bottles, some 750 ml, some full liters) were to, hypothetically, blow for whatever reason, I could lose my fucking furnace.  That is, of course, an absolute “zombie outbreak while an asteroid hits Earth” style worst case scenario.

Thankfully, I’ve yet to lose any bottles to over-carbonation, but like all home brewers, I make sure that I say “yet”. It can happen even if you’re super duper careful. Odds go up if you’re less so.

Can I go get one later?

In the words of that dude from Ratatouille, “Nopity nopity noo.” You need it to get an original gravity measurement, and that measurement varies. A lot. There are online calculators that can help you estimate, but you have no way of knowing how accurate your calculator of choice is until something either goes wrong or doesn’t. A final gravity measurement is about 19 different kinds of useless without an original gravity one; all the math involved is relative.

Here’s the story: I am a cheapass. I have a tendency to not buy equipment until I absolutely need it, and usually not until long after I do. I moved up to five gallon batches from—shit you not—brewing in milk jugs because my local home brew shop had a  primary fermenter (in layman’s terms, a bucket) they were GIVING away. I bought an airlock because it’s a bitch to put a balloon with a hole poked in it over a bucket. I bought a floating dairy thermometer when I got tired of losing my meat thermometer in my pot and having to guess if the must was pasteurized.

So, hydrometer? Psh.

Until, that is, the OCD kicked in. I wanted—I NEEDED—to know how powerful my mead was. I just did. There was an empty space on my labels, and it was driving me clown-shit insane. So I spent the $8 on a hydrometer.


I have five gallons of traditional mead sitting next to my turtle tank (properly vented, of course), and I have no idea what the ABV of it is. I can tell you that I had to repitch the yeast (layman’s terms: make it make booze some more) when it had a specific gravity of 1.050. I can tell you that as of last Saturday it’s sitting at 1.012, meaning that it has gained roughly 5% alcohol since the repitch. But I don’t know where it started, so I can’t know how far it’s come total.

I can’t know.

What about a vinometer? I saw those in the store.

Widely reviled for being based primarily on the concepts of capillary action (sort of) and witchcraft (almost entirely), a vinometer is supposed to measure alcohol content directly. They don’t. According to mine, tap water has a negative alcohol content, and my mystery mead got all the way to 18% ABV—that is, alcoholic enough to kill all the yeast—and continued fermenting, but without producing any alcohol. They are neat looking, though.

A wine weigher?

Hard to find outside of the EU, and a bitch and a half to rig a makeshift version.

A refractometer?

Basically does the same thing as a hydrometer, but with light waves instead of floating. About 5X as expensive, 100X as sturdy, and equally useless at this stage.

An ebulliometer?

I didn’t say you could use Google, and if you used it properly you’d know they’re $300 and up.

So there really is no…

Way around it. No. When I say I can’t know, I mean I can’t know. My options at this point are drinking it while timing myself and then trying to guess while blotto (which I can’t do ’cause I’m pregnant) or sitting in front of the carboy shouting “TELL ME WHAT YOU KNOW” until collapsing into tears. Neither method is known for being terribly accurate.

To sum up: If you make booze, go get a hydrometer. Go. Now. Spare yourself the shrapnel and the confusion.

Run. I’ll hold them off.