Hops: Oils/Acids, Varieties, and the Struggle

Hops are one of the four major ingredients in beer. They provide a complexity through bitterness, aroma, and taste. During the brewing process, they are added during the boil for a length of time dependent on their role in the beer. As the time the hop is exposed to the heat of the boil increases, the flavor components will go from aroma to flavor to bitterness. This is due to the fact that different chemicals are created or driven off depending on the boil time.

Oils and Acids

They glory of hops lies in their oils and acid and each variety contains a unique chemical package. The acids are typically described with two different quantities: %alpha- and %beta- acids. Alpha acids are largely responsible for the bitter flavor in beer, while beta acids contribute to the bitterness to a lesser degree. It is interesting to note that hops high in alpha acids posses strong anti-bacerial properties that promote exclusively brewer's yeast to drive the fermentation (as opposed to countless bacteria).

Alpha acids refer to a class of chemicals that posses a carbon hexagon with branch groups containing ketones and alcohols. Under enough heat, these chemicals can be isomerized. That is, the atoms contained within the molecule will change in relation to one another. Isomerization does not refer to a chemical reaction where atoms are switched between molecules, only a restructuring of the molecule. Heat is required to isomerize the compounds, which is obtained in during the boil. As the hops boil a longer period of time, a greater proportion of the alpha acids are converted to iso-alpha acids, resulting in a more bitter beer. Bittering hops are boiled for at least 45 minutes for most beers. Hops varieties used for bittering will have high levels of alpha acids, up to 20% alpha acid by weight, while those for flavor and aroma can be less than 5% by weight.

Beta-acids differ from alpha-acids in that they cannot be isomerized. However, a chemical reaction with oxygen will yield a compound that is perceived as bitter. Iso-alpha acids will degrade with time, making the oxidation of beta-acids play an important role in lagers and aged beers. The ratio of alpha acids:beta acids changes depending on the variety, but there is almost always more alpha acids than beta acids. The alpha:beta ratio ranges between 1:1 to 2:1.

The majority of the weight in flavor/aroma hops comes from essential oils as opposed to the acids. These oils, which vary in concentration among different varieties, are highly volatile and are driven off during a long boil. Brewers will add these hops either: 1)in the mash which doesn't get above 170degF,  2) in the last few minutes of the boil ( <5 minutes), or 3) into a fermentor in a process called 'dry hopping'. By minimizing the amount of time the hop tissue is exposed to high heat, the volatile compounds are maximized.

Varieties

Noble Hops - Europe. Much like wine, the specific climate and soil conditions have a huge effect on the chemical profile of hops. There are four types of noble hops: tettnang, saaz, haullertau, spalt. These hop varieties are named after the region in which they are grown. Each variety is named after the town or region in which it is cultivated, in the same way burgundy wine is named after the region in France. Geographically speaking, saaz is from the Czech Republic, while the others are from Germany. Noble hops have low levels of alpha- and beta- acids (<5%) and an alpha:beta ratio ≤1. They are renowned for their consistent bitterness with age, and are the most common hop variety in most German/Czech lager and pilsners.

Sorachi Ace - Japan. Sapporo brewing company in Japan developed this hop from Saaz and Brewer's Gold. Their intention was to create a hop that would be similar in flavor to the Czech Saaz, but would possess the intense bittering power of the high alpha acid Brewer's Gold. While it does possess a high alpha acid content, the hop is still viable as a late addition hop due to it's unique lemon/spice flavor and aroma. It was first cultivated in the 1970s in Japan, but the hop wasn't available in the US until 2006. During the hop shortage in 2008, many breweries and home brewers began to experiment with it, with some having commercial success (Brooklyn Sorachi Ace saison).

There are dozens of other hop varieties grown though the US, Canada, and the UK. Each region has its own unique varieties breed for bittering, aroma, or flavor.

The Struggle

Roy Farms Hops

Hops are a pain in the ass to grow and harvest. The picture above shows a typical hop farm. The hops grow on bines which require a trellis for support. As the hops grow up the trellis, it increases the area of sunlight they are exposed to, which in turn increases the total yield of the plant. The trellises are constructed by hand, and are created whenever a new crop is planted. Each spring the vine starts from scratch, and will grow to the top of the trellis by the end of June. Each plant has to be trained by hand to grow up the trellis and not across the ground.

The recent craft explosion has put a strain on the hop growers around the world, particularly the United States. Hops can only be grown in certain regions, and the only areas suitable in the united states are in the northwest (Washington, but some in Idaho and Oregon). While the recent craft beer explosion provides a new market for hop growers, the constant thirst for something new creates demand for new hop varieties. Maintaining a hop crop is hard enough, but to switch between varieties can lead to financial ruin. Hop plants do not produce a crop their first year, so farmers will typically sign contracts with hop distributors guaranteeing that their crop will be purchased for several years regardless of demand. It is for this reason that hops are so damn expensive.