Friday, July 31, 2015

The Science of Brewing

A special submission by Chris Gemmiti, PhD
- Board Member, The Children’s Museum in Easton
- Long-time home brewer
- Bio-Scientist, Wyss Institute for Biologically Inspired Engineering

For those of you who love a fine beer, you’ve likely wondered what magic happens to make that tasty brew so darn good. If so, you’re in luck: in this blog post, I will give you the highlights of the science behind brewing. By the end, hopefully you’ll be convinced that brewing beer is really quite simple–not magic at all–You may even find yourself inspired to give home brewing a try for yourself.

Introduction to the Science of Brewing:


Reinheitsgebot (or “purity order”) is otherwise known as the “German Beer Purity Law,” and serves as the foundation for the original three ingredients of beer:
  • Water
  • Barley
  • Hops

This 1487 law restricted the making of beer to only those ingredients. It
wasn’t until the 19th century that the role of yeast was discovered in fermentation. It was then that it was acknowledged that yeast was central to brewing (previously, wild yeast made its way naturally into the unsuspecting brewer’s batches). The current German Beer Law includes yeast, along with its predecessors of water, barley and hops, as the key ingredients.

You can read more about the history of Reinheitsgebot on the German Beer Institute's Portal for North America.


Barley a member of the grass family is a grain that has wide use in foods, from cereal to soup to bread, and has a great many flavors known as cultivars (read more about barley). For those of us interested in beer (and whiskey), barley is the key source of sugar. That sugar adds not only color and taste to your beer, but is a substrate for fermentation. Prior to making its way into that bottle of beer however, barley must undergo the malting process. Barley, in its raw state, does not contain sugar, but starch. In the malting process, an enzyme (contained in the barley kernel) converts that starch to a sugar. To activate that enzyme, the barley is hydrated with water, warmed to induce germination, and is then dried into malt (or malted barley). One then roasts the malt, akin to toasting, to bring out different flavors and colors very similar to coffee beans. You can see a nice depiction of those malted barley types in "Debunking the Myths Surrounding Dark Beer" by Ashley Rouston and in this online Home Brew Manual, that latter of which has a nice explanation of how those colors are measured using the Standard Reference Method (SRM). If youre interested in home brewing, dont worry: youll have purchased your malted barley completely ready to be used.


While barley adds the color and sweetness (or lack thereof) to beer,
hops add the bitterness and much of the aroma. If youve ever had a strong India Pale Ale (IPA), you know what a beer full of hop character is all about. That character is due to the alpha and beta acids contained in the lupulin glands of the hop cone. The hop cone looks like a lime green acorn with the consistency of a flower. If you peel open a hop, you expose the glands containing those wonderful oils and resins. Hops are planted as rhizomes (looks like ginger root) and grow as tall vines which produce a great many hop cones. You can even plant your own hops and train them to grow up a lattice or pole; easy to order! You can assess how hoppy your beer is by looking on the bottle or package for the IBU, or International Bittering Units; the higher the number, the hoppier the beer. 


Yeast is the microorganism responsible for that conversion of sugar (from the malted barley) to carbon dioxide and alcohol, otherwise known as fermentation. While yeast is the undisputed workhorse of brewing, the two main types of yeast yield the two main types of beer: ales and lagers.

  • Ales come from ale yeast (a “top fermenting” yeast), which start fermentations at relatively higher temperatures (10-25C). 
  • Lagers come from lager yeast (“bottom fermenting”) and undergo a “lagering” process at lower temperatures (7-15C).
The top and bottom descriptor refers to where the yeasty foam layer accumulates during the brewing process. For you science lovers, here is a nice article from Popular Science.

With those three (four, including water) main ingredients covered, let’s step briefly through the (home) brewing process. Note that this is NOT meant to be an instruction set to home-brew, but instead a high-level overview of the process. 

Before actually firing up the stove (or LP tank burner), you’ll need to get your supplies. Home brewing supplies will include both hardware and raw materials. Most folks start off with a 5-gallon batch, which yields 2-3 cases of beer. Pre-made kits (both hardware and materials) are readily available from your local homebrew store, such as Homebrew Emporium, or internet retailers such as Midwest. The starter hardware should set you back $80-100 for a basic outfit, the raw materials about $40-50. If you’re just starting out, I recommend you ‘buy local’ to have one of the excellent staff members help you through the process. Lastly, you’ll also need a proper how-to book to have as a guide and reference. While there are plenty of sources on the internet, a book will stand up to the mess home brewing can create better than your laptop. You can also make handwritten notes in it as you progress in your experience. 

Step 1: Brew
Once you have everything, the process itself it really quite easy so long as you do two things: (1) don’t contaminate anything (no sneezing into your fermenter!) and (2) relax, have a beer. The first step centers on steeping your malted barley in hot water (typically 2-3G in a large pot) to extract all those wonderful flavors and colors. If you’ve made tea before, this is the exact same process (just in a much larger batch!). After a set time, you’ll bring your wort (pronounced “wert”) to a boil and start to add your hops. Hops left in for a long (20-30 minutes) impart a bittering flavor to the beer. Hops boiled for a short (5-15 min) impart the aroma. After that roughly hour or so of boiling, it is time to cool down your “green” beer to a temperature that your yeast will like (depending on what yeast type you’re using). Once it is ready, you’ll combine that wort with yeast, and you’ll tuck your beer away in a dark place (remember: light skunks beer) and let the yeast do their thing. Good news; the (ahem) hard part is over, in just about a half day’s time.

Step 2: Ferment
This is the easiest part of the process; because all you have to do is check in on your fermenter to make sure everything is going to plan. That includes keeping an eye on the temperature (to make sure the yeast remain active), ensuring your fermenter isn’t getting too much light (none at all is ideal), and making sure you haven’t made a mess. Your yeast should be bubbling away and “burping” carbon dioxide (CO2). Your beer will take at least 2 weeks to ferment, but most home brewers leave it be for 4-6 weeks to allow for the most complete fermentation.

Step 3: Bottle (or Keg)
As the penultimate step, you’ll be ready to bottle (or keg) your beer. Hopefully you’ve been saving (and rinsing!) about 2-3 cases worth of 12oz bottles to store your beer; obviously you can also buy them new. Assuming you’re bottling, you’ll add some priming sugar to each to allow for carbonation to naturally build up during the bottling phase. If you’re kegging, you’ll skip the priming sugar as you’ll be force-carbonating using your CO2 tank. Either way, you’ll want to allow for anywhere between 2-6 weeks to get the right carbonation set up. Of course, periodic sampling is encouraged to track the progress.

Step 4: Drink!  (And repeat)
After our roughly two month journey, viola, we have beer! Now comes the part we’ve all been waiting for: drink your beer! Most home brewers are surprised and thrilled at the accomplishment of making pretty darn good tasting beer on their first try. We hope you do the same; so much so that you try another batch!

In conclusion, brewing beer is as easy as it is fun. As with most things, you can make it as difficult and expensive as you want, but happily, you can get going with a fairly modest investment of time and money. As you grow as a brewer, you’ll try new tricks and beers, and show off to your friends what a wonderful home brewer you’ve become!


This article kicks off our blog for our 2nd annual Night At The Brewseum, a craft beer expo featuring tastings from local craft beers & ciders. The event scheduled for August 22, 2015 also features a home brewing competition, food, music, and a science of brewing exhibit. Tickets are on sale now! Click here for details and tickets.

Image sources:

No comments:

Post a Comment