Praxis and Practice
Over the past couple of years, I've become increasingly dedicated to brewing beer at home with a good friend of mine. At first, you would think that the biggest benefit of that hobby would be lots of great, cheap beer on tap. (And that part is awesome.) The absolute best part, though? A hands-on education in chemistry, physics, fluid mechanics and history.
Need. Learn. Solve.
The best hobbies force us into a continuous cycle of frustration and triumph — victories that can only be achieved by connecting your brain directly to your hands. Homebrewing isn't rewarding because it's so hard — it's surprisingly easy to brew a decent beer at home — but because there's always something to improve. Something that you could have done better. Something you could have done faster. Anything that would have gotten you closer to where you really wanted to be.
Better Bitter Beer, Bitte?
The "standard" size for a homebrew beer recipe is 5 gallons. Not only is it that a nice, round number, but it's also the upper limit of what you can easily manage on a stovetop. Since my buddy Phil and I always brew together, though — and we were already using an outside propane burner setup — we quickly graduated to 10-gallon batches. In principle, that's simple enough. All you have to do is double your recipes, and make sure your vessels are big enough to handle the bigger volume of liquid.
In practice, though, we found we had a consistent challenge — our bigger batches were continually turning out much more bitter than we had intended. Even when we went back and carefully re-made doubled-up versions of our 5-gallon recipes, the 10-gallon batches were noticeably more bitter, which (technically) is not what's supposed to happen.
Better Taste Through Chemistry. And Physics.
After digging around and thinking it through a bit, we started to understand what was going on. The actual issue was pretty simple — once we were supposed to be "done" boiling a 10-gallon batch, our beer was still staying much too hot, for much too long.
Bitterness = Acidity * Weight * Time
The underlying cause is the biochemistry of hops. Fresh hops have the same aromas and flavors we're used to in beer, because those come from the essential oils that the plant produces. On the other hand, they really don't taste very bitter at all, because those bitterness-causing compounds don't exist naturally in the plant.The Bitterness Balance»
The hop plant does contain bitter compounds known as humulones, but in their natural state, they're not very soluble in water. At room temperature, you could throw handfuls into your beer, and it wouldn't taste much more bitter. (It would taste different, just not a lot more bitter.) At temperatures closer to boiling water, though, the humulones start to form isomers — each humulone molecule keeps exactly the same atoms, but the extra energy helps the atoms jump into a different configuration. That new structure gives the molecule new properties.
These new isomers happen to be much more soluble in water, and so they leave the plant and start adding their bitterness to the beer. The formula to predict final bitterness is pretty straightforward. It's basically a function of the natural bitterness of your hops, how much of them you use, and how then long you keep them close to boiling.
A Lingering Loss
The compounding factor was the volume of our beer...or, more specifically, the volume-to-area ratio. At this point, most of us are familiar with the geometry of why large mammals like elephants have body temperature issues compared to little mammals like mice — their heat-producing volume goes up as a cube, while their heat-dissipating surface only increases as a square.
When you allow for the fact that — thermodynamically speaking — mammals are pretty much just mobile sacks of warm liquid, it's clear that we face the same issue with beer. When you go from 5 gallons to 10 gallons, the volume of boiling hot liquid goes up as a cube, but the cooling area only grows as a square. It doesn't really matter on the way up if it takes longer to reach boiling, because the hops aren't adding bitterness yet, but it makes a huge difference once you're trying to cool the beer, and get them to stop...especially if you're trying to do it by sucking the heat out through the sides and bottom of the pot.
At the time, that was our approach. We would take the pot of boiling wort, and dunk it into a bucket of ice and cold water, and then stir the beer briskly to cool it down. With a 5-gallon batch, that's workable, because you can get the pot down from 212F / 100C to 80F / 27C in about half an hour. That means the hops stay hot enough to keep bittering for maybe another 10 mins, and then they become too cool to really add any more bite. For a 10 gallon batch, though, it can an hour or more to cool down the wort, which means the hops continue to add bitterness for an extra 30-40 minutes before they're cool enough to stop.
The Answer? Make More Stuff.
It was fundamentally an issue of thermodynamic conductivity, or the rate at which we were extracting energy / heat from the boiling wort. We needed to use a much more efficient approach.
I won't pretend that we came up with a unique approach — we basically just adopted a standard tool that other brewers figured out decades ago, and thousands of people have used since, called a "wort chiller". What was new for us was a much more intuitive grasp of why we needed it.
We had obviously seen them before, but we just considered them kind of a luxury, something that made life easier. As soon as we figured out what was really going on with our bitterness, though, we both immediately looked at each other and said "Oh...duh! We need a wort chiller!"
This Copper Coil
You can easily buy pre-fabricated wort chillers at any homebrew store,
There are two important factors that influence the final taste of a beer: bitterness and maltiness (i.e., sweetness).
- IBUs: The bitterness of a beer is measured in International Bitterness Units, a somewhat arbitrary unit that can only be determined in a lab. When making a beer at home, you can calculate what the final IBUs of your recipe should be, based on your hops, but there's no easy way to measure exactly what it is, in the end.
- OG: The sugars in a beer are measured by its density, or specific gravity. Most of the sugars that are initially in a beer will be converted into alcohol, but the density of sugars before fermentation (Original Gravity) is a good measure of how malty and sweet the final beer will taste. You can — and should — measure the gravity of your beer throughout the brewing process.
A well-balanced beer will have an IBU/OG ratio close to 0.5, and beers that are especially bitter will have ratios closer to 1.0. All the recipes we had made were designed to be pretty balanced, usually right around 0.5 or so.Powered by Hackadelic Sliding Notes 1.6.5