The Science behind Beer

During ancient times, beer was intended to be liquid bread. To provide the nutrition and satiation of bread, it used the same raw ingredient, grains. But what is the secret ingredient that makes this liquid grain emulsion into beer?  It’s yeast!  Yeast is the catalyst of brewing as it turns sugars into alcohol and carbon dioxide, giving the beer its carbonation. So, let’s go in depth into the beer brewing process.

Malt – the first ingredient

Malted Barley
Photo credit: epicbeer

In the beginning, raw grains are very starchy and have little sugar.  Because of this, the starch needs to be broken down into sugar before the yeast can consume it as energy.  The first beer brewers found that this breakdown process came naturally whenever grains would first germinate.  When a grain is very young and needs to grow, it transforms its starch into sugar, making it easier to convert into energy for growth.  In order to deconstruct the starch, it releases an enzyme called alpha amylase. This protein enzyme breaks down the long chain starches into the smaller chemicals of glucose and maltose.  In turn, these sugars are very easily converted into energy.

Originally, many grains were experimented with for this process, including wheat, rice and barley.  Eventually barley became the defacto grain due it being highly efficient in naturally creating the alpha amylase enzyme to breakdown its own starches.

In order to have the barley germinate and kick start this sugar creation process, the grain was usually left to sit in a vat of water to start the sprouting process.  When the barley is on the verge of sprouting, the sugar levels are at their highest.  This germinated grain is now called malt. At this point, the brewer wants to stop the sprouting process of the malt so that the sugar can be used to feed the yeast instead.    To stop it, the malt is roasted dry.

The roasting process is vital to the type of beer being created.  It gives the beer its color, or lack thereof, and flavor.  For pale beers, the malt is lightly roasted usually around 80 degrees Celsius, whereas for dark beers such as stouts, the beer is highly roasted at up to 180 degrees Celsius.  The strongly roasted malt gives rise to the coffee and cocoa like flavors that can be tasted in dark beers.

Now that there is dried malt, it needs to be liquefied  to create and capture the remaining sugars.  In order to do this, the brewer crushes the dried malt grain, known as mashing, and then adds hot water.

Mash
Photo credit: epicbeer

The hot water reactivates the enzymes in the grain and converts the remaining starches into sugars.  The solids left from the mashing drop to the bottom and the resulting sugary liquid stays at the top.  This liquid mash is used to create the “wort”.

Creating the Wort

Now that we have the liquid mash of extracted malt sugars, we need to add water and boil it to remove any foreign bacteria and add the other flavoring and preservation ingredient, the hops. This resulting liquid is called the wort.  But first, don’t forget about the most abundant ingredient in beer, the water!  The type of water used greatly affects the taste of the beer.  Many types of beer are known for their breweries’ local water. Pilsen, the origin of pilsners, is known for its very soft water.  English Pale Ales were known for their hard water, which gave them a bitter sulphate taste!

Now for our other ingredient, the hops.  Originally, beer was made without hops and instead used spices and herbs to balance out the sweetness of the malt’s sugars and the sourness created as the byproduct of foreign bacteria.  However, hops and their oils provide various aromas and flavors, including a nice bittering balance to the malt, and also preserve the beer with its disinfecting properties.

hops
Photo credit: Paul Miller

The bitterness in hops comes from its alpha acids.  In addition, these alpha acids create a bateriostatic environment, inhibiting the reproduction of bacteria.  Also, the amount of alpha acids in the hops affects how bitter the beer will be.  The oils in hops provide the various floral and citrusy aroma found in beers.

Because of these properties, hops, like barley, became the predominant ingredient in beer brewing. To extract these properties from hops, the hops are added in during the boiling process.

The boiling process can take 60 to 90 minutes, depending on the type of beer being created.  Hops added during the beginning of the boil provide the desired bitterness of the beer.  Hops added toward the end of the boil imbue the beer with its aromatic oils.

Once the boil is finished, the hot wort is then cooled to provide the right temperature for our final main ingredient, the yeast.

Yeast and the Fermentation Process

Before we get into how yeasts are used in brewing, let’s talk about what they are.

yeast-microscope
Photo credit: bill rix

Yeast are single celled organisms that break down sugars using a process called glycolysis into energy for reproduction purposes which also releases alcohol and carbon dioxide as by-products. This process in brewing is known as fermentation. There are many species of yeast, with each producing slightly different chemical byproducts known as esters. In addition, certain yeast species like specific environments in order to grow.  In beer, the biggest environmental factors are temperature and sugar/alcohol levels.  This differentiation separates the various types of beer.

Two main categories exist in beer yeast.  The first is top fermenting yeast, Saccharomyces cerevisiae, which ferments in room temperature environments and rises to the top during the process.  It is used for making ales.  Saccharomyces pastorianus, bottom fermenting yeast, needs cooler temperatures around 45 – 50 degrees Fahrenheit and is used for making lagers. Ale yeast takes 1 to 2 weeks to complete the fermentation process, whereas lager yeast ferments more slowly, sometimes for 8 weeks.

Now back to the brewing process. After the wort is cooled to the desired yeast temperature, the yeast is added.  Right before this, the beer’s gravity, its density compared to water, is measured. After fermentation, the gravity will be taken again to measure the amount of alcohol that was produced, since alcohol is less dense than the original sugary water.

After the yeast is added, the beer is sealed so that no outside yeast or bacteria can enter the beer during the fermentation process, removing the risk of any unwanted alteration of the flavor.  A one way out valve allows the CO2 to escape during fermentation.

fermenting-beer
Photo credit: ilovebutter

Once the allotted time for fermentation has expired, the final gravity is measured to determine the readiness of the beer – usually judged by the alcohol percentage.  When this final gravity is reached, the CO2 valve is sealed and the remaining fermentation carbonates the beer.

After the fermentation process has completely finished, the beer is usually cooled to 32 degrees which separates the yeasts, proteins and other solids from the beer. The beer is then siphoned off and is now in its final form and ready for storage.

Storing Beer

Beer is stored in a variety of ways – kegs, bottles, and cans.  In order to preserve the qualities of the beer, the beer must stay away from any additional oxygen and contamination from foreign organisms such as bacteria and yeast.

In bottling, the bottles are rinsed with a sterilizing solution and then quickly dried by pressurized CO2.  Beer is then quickly added to these pressurized bottles and sealed with a cap.

In kegging, the keg is sterilized and pressurized with CO2. The beer is then pumped in until it is full.

In canning, beer is added to the sterilized can and then quickly sealed by crimping the beer can top onto the body.