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Fermentation of beer

Lager beer

Beer is one of the most popular alcohol containing drinks consumed and the third most popular drink in the world. Being one of the oldest recorded drinks made, it's history runs parallel with the history of the world.

The basic ingredients of beer are malted barley, hops, water and yeast. Some brewers add wheat, oats, rice, or corn. Beers can vary in flavour based on the grain used, duration of fermentation, temperature maintained, type of yeast used, etc. There are about 400 types of beer. Beers can broadly be divided into Ales and Lagers. These can be further divided into various types. For example, Pilsner is one of the most popular lager styles and Porter and Stout are examples of ale styles. The alcohol content can usually be determined by the colour of the beer, light being weak and dark being strong.

There are about 150 calories in a 12-ounce serving of standard beer, A light beer will contain roughly 100 calories and some hefty styles contain about 300 calories.

The process of making carbon dioxide and ethyl alcohol (the alcohol in beer) from glucose using yeast under anaerobic conditions is known as Fermentation. With specificity to Beer, the process of fermentation is known as brewing.

History of Beer

pictograms of beer allocation (London)

Ancient pottery jug

Beer is the oldest recorded recipe in the world.

The Sumerians settled upon the plains, creating a civilization. They began to grow the grains, making them into a form of bread called bappir. In the oldest written recipe known to archaeologists, they praised the goddess Ninkasi (Brewer to the gods) for teaching mankind to make beer too, which they called kas. The Babylonians on conquering Sumer learnt the art of brewing beer. It soon became an important part of Egyptian culture and as it was far healthier than water, it became the everyday drink of the Egyptian people, from Pharaoh to the lowliest peasant. Great grain stores were built, and the Egyptian economy was underpinned by bread and beer.The god Osiris held in his hands the very stuff of life—fertility, death, resurrection, and the brewing staff. The ancient Egyptians first documented the brewing process on papyrus scrolls around 5,000 B.C. These first beers were brewed with things like dates, pomegranates, and other indigenous herbs and Barley.

Beer eventually made its way from the Middle East to Europe, where it became an integral part of life. This was especially true in Northern Europe where abundant barley crops provided ample raw ingredients for brewers. Beer was a safe alternative to drinking water, many sources of which had become contaminated with human waste. All the brewers of that time are known to have been women. Brewing beer was considered a noble task for women and only women from elite backgrounds had the privilege to brew beer. Brewster is the term used for a women who brews beer.

Records of modern beer can be traced to the middle ages. Brewers had been using malted barley as the main source of fermentable sugar for hundreds of years and balancing the flavour with everything from spruce boughs to dried flowers to bitter roots and many different herbs and spices. In roughly 1150, German monks began commonly using wild hops in beer and the ingredient quickly caught on. Brewers found that hops added a very pleasing, thirst quenching bitterness and, as an added benefit, the hops acted as a natural preservative extending the life of their beers. Historians credit monks with many brewing innovations apart from the introduction of hops, including the idea of lagering/cold storing beer to improve flavor. Virtually every monastery had a brewery on site Even in modern times the monastic brewing tradition holds, with a number of Belgian monasteries ranking today among the greatest breweries in the world. The oldest brewery has been functioning for around a 1000 years now. Weihenstephan Abbey in Germany is the world's oldest operating brewery that flagged off centuries ago in 1050.

Along with Northern European countries like Germany and Belgium, the British Isles too, became a brewing center.

Production of beer

Barley that is malted

Hops used for flavouring

Saccharomyces cerevisiae

Raw materials

Barley:

Before barley can be used to make beer, it must be malted. First, the barley must be allowed to germinate. This is done by soaking the barley in water for several days, and then draining the barley and holding it at about 15.5°C for five days. This allows the husk to open and barley to start sprouting. At this point it is called green malt. The key to the malting process is to stop the germination of the barley at a point when the sugar-producing enzymes are present but most of the starch is still unconverted. Eventually, these enzymes will produce the sugars that will feed the yeast to make the alcohol in the beer.

After this natural process has released the enzymes, the green malt is dried by gradually raising the temperature. The intensity of the malt flavor and color depends on how high the temperature is raised during the drying process. The final step is removing any small roots that formed during germination. The malted barley is ready to begin the brewing process.

Hops:

The hops used to make beer are the flower of the hop vine, which is a member of the hemp family (Cannabaceae). Hops are closely related to another member of the hemp family (such as cannabis, or marijuana) but lack the psychoactive effects.

Hops provide the bitterness to beer (via the acids it contains), its flavor and aroma (the oils it has )and it also inhibits the formation of certain bacteria that can reduce it’s shelf life.

Yeast:

Common Yeast is also called Baker's/ Brewer's Yeast and its scientific name is Saccharomyces cerevisiae. There are two main categories of beer yeast: ale yeast and lager yeast. Ale yeast is top fermenting it rises near the surface of the beer during fermentation) and typically prefers to ferment at temperatures of 21°C. Lager yeasts are bottom fermenting. They ferment much slower and perform better at colder temperatures (around 10°C).The yeast can be reused a number of times before it needs to be replaced. It is replaced when it has mutated and produces a different taste.

Water:

Water plays an important role in beer production. It is used in the beer as well as in the machinery used to make beer. IT is used for extraction of sugars from the barley as well as in maintaining temperature of the beer at various steps in the process of beer production. It is also used to help seal the beer bottles.

Pre-fermentation process

Step 1: The mash

Mash for extraction of fermentable sugars

In this process starches in the malted barley are converted into fermentable sugars. If the kernel of barley is broken up just enough, then when the mash is finished, the whole husks form a filter bed that captures any solids from the liquid; but if the husks are broken down too much, they clog up and don't let the liquid through.

The crushed grains are then passed through a feed pipe into the mash-lauter-tun. This insulated vessel has a device called a hydrator whose purpose is to spray heated water onto the grains as they enter. This eliminates any dry spots (hence wasted sugars) in the mash. The wet grains stay in the vessel for an hour. at around 65°C.

The last steps needed to complete the mash are lautering and sparging. The liquid is drained from the bottom of the vessel and then recirculated to the top so that it is filtered through the husks of the spent grains. Additional heated water is then poured over the grains (in a process called sparging ) to make sure all of the sugars are removed.

Before the mash starts, the grains aren’t sweet, but the liquid that is drained off from the grains at the end of the mash is very sweet and sticky. This liquid, which now contains mostly fermentable sugars, goes on to the boil.

Step 2: The boil

Brew kettles for the boil

The next step is the boil. At the end of the boil we will have a finished wort.

To start, the liquid from the mash is put into a huge steam jacketed brew kettle. This kettle has double walls with a gap between them through which steam is circulated to provide  even heating. The temperature is raised until the liquid comes to a vigorous rolling boil, and it is held there for 90 minutes.

At the beginning of the boil, hops are added. These are called the boiling hops. The acids that produce bitterness in the beer are not easy to extract from the hops, which is why they need to be boiled for up to 90 minutes. The oils that produce the hop flavor and aroma are very volatile and evaporate quickly, so the boiling hops only contribute bitterness to the beer.

Depending on what type of beer is being brewed, more hops may be added near the end of the boil and are called finishing hops. Generally, these are added 15 minutes before the end and contribute flavor and aroma to the beer.

Step 3: separation of solids

Before the wort can go on to the next step, all of the solids must be separated from the liquid. The wort is pumped from the kettle, and forced back into the kettle via a jet nozzle. This flow of liquid causes the formation of a whirlpool. Which results in all of the hops and other solids move to the center. The pump is then turned off, and over the next 20 minutes the whirlpool gradually stops and the solids settle to the bottom, forming a fairly solid cone. When the wort is drained, the solids stay in the kettle.

The wort needs to be cooled down to the proper temperature for the yeast. This is done in a liquid-to-liquid heat exchanger. The tubes with hot wort running through them transfer heat to the tubes holding the chilled water. It is important to cool the wort quickly so that the yeast can be added right away and fermentation can begin. This reduces the chance of contamination by stray yeasts floating around in the air.

Fermentation of beer

Fermentation tanks/ fermenters

Fermentation is the process by which yeast converts the glucose in the wort to ethyl alcohol and carbon dioxide gas anaerobically- giving the beer both its alcohol content and its carbonation.

The process of fermentation begins when the cooled wort is transferred into a fermentation vessel to which the yeast has already been added. Based on the type of beer being made the temperature and duration maintained varies ( Ale- 20°C, 2 weeks; Lager -9°C,6 weeks). The tanks must be cooled constantly to maintain the proper temperature.

When the wort is first added to the yeast, the specific gravity of the mixture is measured and it is measured again after certain duration to determine how much alcohol is in the beer, hence, when to stop the fermentation process.

The fermenter is sealed off from the air except for a long narrow vent pipe, which allows a constant flow of carbon dioxide to escape from the fermenter, preventing outside air from entering the fermenter, reducing the threat of contamination by stray yeasts.

When fermentation is nearly complete, in case of lager, most of the yeast will settle to the bottom of the fermenter. The bottom of the fermenter is cone shaped, making it easy to capture and remove the yeast, which is reused in the next batch of beer.

While fermentation is still happening, and when the specific gravity has reached a predetermined level, the carbon dioxide vent tube is capped, causing pressure to build as CO₂ continues to be produced. This is how the beer gets most of its carbonation. From this point on, the beer will remain under pressure.

When fermentation is complete, the beer is cooled to about 0°C. This helps the remaining yeast settle to the bottom of the fermenter, along with other undesirable proteins that come out of solution at this lower temperature.

Now that most of the solids have settled to the bottom, the beer is slowly pumped from the fermenter and filtered to remove any remaining solids to another tank, called a bright beer tank. This is its last stop before bottling or kegging. Here, the level of carbon dioxide is adjusted by bubbling a little extra CO₂ into the beer via porous stones.

Kegging machine for industrial purposes

Bottling of beer

The crucial thing in the bottling and kegging process is to keep the beer from being contaminated by stray yeasts and to keep oxygen away from the beer.

The process starts with empty bottles being loaded onto the bottling line, where they are rinsed with a chlorine solution  then blasted with CO₂ to remove the solution.The bottles then enter a turret-like mechanism that can hold quite a few bottles at once. Each bottle rides around the turret one time and during this the bottle is purged with CO₂ several times before it is filled. The bottles are pressurized with CO₂ to prevent foam build up when beer is added. After the beer has been added, the pressure is slowly relieved until the beer is at ambient pressure.Capping of the bottles follows. There exists a little bit of air space at the top of the bottle that needs to be removed. To do this, the bottle is passed under a very narrow, high-pressure jet of water that hits the beer, causing it to foam up and drive the air out of the bottle. The cap is then applied before any air can re-enter the bottle.After the cap is applied, the outside of the bottle is rinsed to remove any beer that may have foamed out during the process.

This is then followed by labeling and stamping and then it is ready for distribution.

Steps involved in the process of glycolysis.

Conversion of pyruvate to ethanol

Chemistry of fermentation

There are two different types of enzymes in the malted barley: alpha-amylase and beta-amylase. The alpha enzymes is responsible for breaking up the long chains of starches by splitting them in half. The beta enzymes breaks down the starches by chopping them off a couple at a time from the ends of the chain. Only if these two enzymes in a coherent manner can the conversion be accomplished. The problem that arises is that the alpha enzymes are most active at 65 to 67°C, and the beta enzymes are most active at 52 to 62°C. So the temperature and duration of the mash must be carefully controlled to get a good conversion.

When the yeast first hits the wort, concentrations of glucose (C₆H₁₂O₆) are very high, so through diffusion, glucose enters the yeast. As each glucose molecule enters the yeast, it is broken down in a 10-step process called glycolysis. The product of glycolysis is two three-carbon sugars, called pyruvate, and some ATP, which supplies energy to the yeast and allows it to multiply. The two pyruvates are then converted by the yeast into carbon dioxide (CO₂) and ethanol (CH₃CH₂OH, which is the alcohol in beer).

Home brewing

Home brewing

At home-brewing stores you can buy malt extract, which is the fermentable sugars extracted from the mash. One can also do a mash at home. A basic set of homebrewing equipment consists of:

• Fermentation vessels (a bucket or glass water jug)
• Various hoses for siphoning beer from one container to another or to fill bottles
• An airlock so that carbon dioxide can escape the fermentation vessel but air cannot get in
• Some cleaning equipment for washing your fermenters, bottles and hoses
• Floating thermometer
• Floating hydrometer
• Bottle capper
• Funnel