BEER CLINIC :: The Hops Project Pt 1

by Dr. Carol Westbrook on May 6, 2014

Ed. This is a 2 part piece about a super hop IPA brewed by our Beer Doctor, Carol Westbrook. Look for the second part in a couple days

Cascade Hops Pellets

Cascade Hops Pellets

The hops project began at Christmas, when I was given a 1-pound bag of Cascade hop pellets, ready for brewing. The hops were harvested in the fall of 2013, at my in-laws’ hop farm in Michigan, Empire Hops and Apples.

One pound is a lot of hops for a home brewer, enough to make 16 five-gallon batches of IPA! I could never hope to give away 80 gallons of beer in a year, much less consume it. My solution: put more hops in each batch of beer. I wasn’t sure my standard IPA recipe would hold up to five times more hops, and I would almost certainly have to increase the malt and alcohol content of the beer; in other words, I would probably have to create a new recipe for an ultra-hopped IPA. Before going ahead with this challenge I realized that I needed to learn more about hops. Thus, the hops project began. I approached this like a laboratory research project: First, the background research into the biochemistry of hops; next, ask the experts for advice; finally, the field work–create my brew and compare it to a variety of hoppy ales.

Hops, as you know, are the flowers of the hop vine– humulus lupulus, to be exact. They contain a variety of compounds that add bitterness, flavor and aroma to the beer. The main flavor comes from alpha acids, beta acids, and volatile oils.

Fresh or dried hops are added to the boiling wort (malt, sugar, and water) prior to fermentation, to add bitterness and flavor to the beer. Hops can also be added after fermentation is complete and allowed to steep for a few days, almost like a teabag; this process, called “dry hopping” adds hop aroma but little flavor.

The chemistry of these processes is fairly well understood nowadays. Hops contain a mixture of “alpha acids,” of which the main compound is humulone. Humulone is not very soluble, but prolonged boiling converts it into iso-humulene, which is very water soluble. Hops producers give the percentage of total alpha acid units by weight (AAU), and are an indication of how much bitterness can theoretically be extracted during brewing. Alpha acids are the main flavor component of American hops, such as Cascade, Centennial, Wilmette, Citra, Simcoe, etc. American hops are the major taste in IPAs and American Ales, and their flavors are described as citrus, grapefruit, piney, fruity. Home brewers make use of the AAU% to estimate the level of bitterness (hoppiness) that their brew will achieve.

Hops also contain “beta acids”. Beta acids do not require boiling, but develop their bitter flavor by oxidation during fermentation and storage. They are an important component of Noble hops, which are Hellertau, Spalt, Tettnang and Czech Saaz. You will recognize them as the main flavor of German lagers, providing a smooth bitterness and spicy, peppery, or floral taste. American home brewers generally don’t take into consideration the beta acid content of their hops (which are generally not provided by retail hops suppliers) but they are important to commercial brewers.

Another notable component of hops is the essential oils, of which one of the most important is humulene. Humulene is thought to give the “noble” character to Noble hops. These essential oils are quite volatile, so they are driven off by boiling. Because of this volatility you can smell them more easily than you can taste them, and they are put into a beer by dry-hopping. Essential oils are an important flavor element in English hops (Fuggles, East Kent Goldings, etc.), which are otherwise low in alpha hops. English hops are described a herbal, grassy, earthy, fruity. Many American hops also contain high levels of essential oils and can be used for dry-hopping as well as bittering (boiling).

And then there is … everything else. Sometimes it is the minor aromatics and chemicals that are present in small amounts that provide the distinctive flavor to other hop varieties. A good brewer or beer drinker can taste the differences.

Prior to tasting a new beer, I would like to know how hoppy I could expect it to be.   A measure of the hoppiness (also called bitterness) is provided by the IBU, International Bittering Unit. In a commercial brewery, the IBU is determined by chemical analysis, using a spectrophotometer to measure the total content of alpha acids. We home brewers don’t have access to a spectrophotometer, so we generally calculate an approximate IBU based on the AAUs of the hops that we added and a few other fudge factors. For example, my Cascade hops were labeled as 9.3% AAU (Alpha acid units). If I used 4 times the amount of hops from my usual brew, my calculations suggested I would achieve 166 IBU. This would need more malt and higher alcohol — a double IPA. I decided to go for it.

imagesDr. Westbrook’s invaluable book, Ask an Oncologist is available through Amazon and Barnes and Noble.

{ 2 comments… read them below or add one }

Katharine May 1, 2014 at 11:39 pm

I love this analysis, and now understand a lot more about how hops figure into beer. I observed much of the process in the past couple years, and have had lots of various explanations, but this puts it all together. Nice to see an article by a scientist who is also a beer expert and appreciator of the art of making beer.
And you know we are partial to the Empire hops! Your beer is going to come out great. Hoppy like I prefer it!


Doug Greener May 5, 2014 at 2:58 am

I agree. A good introduction for the uninitiated, especially those who believe that it’s the hops that make the beer.
Doug Greener


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