Chemistry of beer, part II: Hops to keg

Hops, the plural form of hop, are a key flavoring agent in beer. After enzymes transform grain into sweet wort during brewing, hops are added to balance sweetness with bitterness and enhance aroma. The boiling process halts enzymatic activity while extracting essential compounds from hops that contribute to beer's unique taste.

Historically, plain fermented wort was considered bland and overly sweet. To enhance flavor, medieval Europeans roasted malts for beer to create non-fermentable sugars that added sweetness. They balanced this with gruit—a mix of herbs like mugwort, whorehound, and yarrow—offering a bitter contrast. Bitter flavors in drinks have remained popular globally due to their unique appeal despite bitterness being less favored in food.

Historically, bittering agents were added to balance the sweetness in beer or ale. In Middle and Early Modern English, a brew flavored with gruet was referred to as ale. By the 15th century, "beer" began describing a distinct type of brew imported from present-day Netherlands and Belgium.

In regions like Germany and the Low Countries, hops replaced gruet in brewing due to economic incentives. Local authorities taxed or monopolized gruet sales as a way of indirectly taxing beer production. Brewers likely turned to hops, an indigenous vine across Eurasia and the Americas, for cost-saving reasons. Dr. Nathan Duncan highlights that hop cones are actually flowers of female plants with varieties offering bittering qualities or herbal/citrusy flavors.

Hops share a close relationship with cannabis due to their similar sensory qualities, stemming from shared compounds. The anatomy of hops reveals lupulin glands within the cone, which produce yellow specks containing hop oils and resins. These substances are extremely bitter but hold most of the desired extractable compounds for brewing purposes.

Hops, specifically alpha acids or humulones, are essential for beer's bitterness. During brewing, hops undergo an isomerization reaction when boiled for at least 60 minutes; this transforms their chemical structure into a more bitter form. In styles like Scottish ales, minimal hops balance the malt sweetness without overpowering it. Conversely, India Pale Ales (IPAs) use abundant hops not only to enhance flavor but also as natural preservatives that prevent bacterial growth and spoilage during long transport.

Hops historically preserved beer during colonial times, much like how modern tools protect digital safety. Surfshark VPN enhances online security by encrypting data on shared networks and bypassing geographic restrictions or censorship. Beyond being a VPN, it offers antivirus protection for Android and Windows devices as well as identity theft prevention through its alert system that monitors emails, passwords, user IDs, and credit cards for potential breaches.

The Role of Terpenes in Brewing and Flavor Terpenes, a class of hydrocarbons found in plants, are responsible for the aromatic qualities of hops used in brewing. These compounds contribute to flavors like piney, citrusy, or floral notes but are highly volatile and can evaporate during boiling. Brewers add hops at various stages—20 minutes before boiling ends or even after turning off the heat—to retain specific terpenes based on their molecular weight and volatility.

Cooling Wort and Yeast Fermentation Process After boiling wort with hops, it must be cooled quickly using copper coils to prevent microbial contamination while sterilizing all tools involved. Once cooled sufficiently to avoid killing yeast cells (Saccharomyces cerevisiae), brewers pitch yeast into fermenters where fermentation begins under controlled conditions. The process involves selective strains bred over centuries for desired traits such as alcohol production; airlocks ensure CO2 escapes without allowing contaminants inside.

Ale and lager differ primarily in the yeast used for fermentation. Ales are brewed with Saccharomyces cerevisiae, which ferments at room temperature, while lagers use Saccharomyces pastorianus, fermenting at colder temperatures over a longer period. Historically, "ale" referred to brews flavored with gruet and "beer" to those flavored with hops; today all beer uses hops but retains these distinctions based on brewing methods.

Lager beer, known for its light and crisp qualities, may have origins in South America a thousand years ago or with Bavarian monks who discovered cold fermentation in alpine caves. In the U.S., lagers dominate due to German immigrant influence and their broad appeal compared to ales. Dry hopping enhances flavor by adding hops during fermentation without introducing excessive bitterness; it primarily extracts terpenes while leaving bitter compounds behind. Yeast plays a crucial role by metabolizing terpenes into new flavors through bioconversion—a focus of Dr. Duncan's research at Maryville College where variations are tested to study terpene effects on beer characteristics.

Flocculation occurs when yeast cells, after consuming all available sugar or reaching high alcohol levels, go dormant and settle out as clumps. This process is essential for separating the yeast from the beer during brewing. The settled yeast can be dried to create powdered forms like active dry or brewer's yeast. To finalize brewing, carbonation is introduced under conditioning to enhance flavor and texture.

Historically, breweries sold their yeast to bakers for bread-making. Today, they supply it not only to bakers but also for producing products like yeast extracts such as Marmite or Vegemite. After brewing flat beer, carbonation is achieved by adding sugar and sealing the container—allowing fermentation pressure to build up.

Bottle conditioning involves adding a precise amount of priming sugar, such as table or malt sugar, to initiate secondary fermentation under pressure. This process dissolves CO2 into the beer, creating carbonation that emerges when opened. Insufficient yeast or sugar results in flat beer; too much can cause dangerous over-carbonation leading to bottle explosions. Over time during conditioning—typically two weeks—the flavor improves due to chemical changes within the sealed environment. Many brewers now prefer force carbonating with CO2 tanks for control and avoiding sediment buildup from additional yeast propagation.

Sanitizing bottles or kegs is crucial during the beer conditioning period to ensure safety and quality. Yeast cannot metabolize starch, leaving unconverted starch that contributes calories but can also attract bacteria if sterilization isn't thorough. Certain bacteria, known as "gusher" bacteria, thrive on this residual starch and cause excessive carbonation leading to explosive bottle openings.

The journey into brewing is both rewarding and risky, as illustrated by a unique beer named "Pearson’s Dumpster Fire." This smoky Scottish ale was inspired by an actual dumpster fire at Maryville College in 2019. Students from the college created this recipe during their beer class, naming it after the lingering smoke smell near Pearson’s Hall cafeteria. The story highlights how brewing connects people to history and practical skills while ensuring there will always be demand for good beer.