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OU CHEM 4970: Chemistry of Beer

CHEM 4970: Chemistry of Beer

Overview of Brewing

  • Critical ingredients for alcohol include sugar and wild yeast
  • Beer is carbonated, unlike other alcoholic beverages

History

  • Oldest produced beverage, dating back to 5000-4000 BC (written documents explain the process) in ancient Egypt & Mesopotamia
  • Ale was probably discovered as an accident, by leaving a bushel of grain in a container that could hold water until wild yeast grew and fermented the grain's sugar into alcohol.
  • 700 AD: introduction of hops & beer purity laws in Germany & Belgium (water, barley, hops)
  • With the later invention of the microscope, yeast was discovered.
    • The beer purity laws were then revised to include yeast.
    • Yeast selection became possible, and thus lager was invented.
  • Boiling process provided a safer beverage during the black plague

Ingredients

Water

Important attributes:

  • Ensures yeast processes carbohydrates
  • pH
  • Calcium
  • Magnesium important
  • Minerals affect mouthfeel

Malted barley (grain)

Important attributes:

  • Carbohydrates
    • Main source of sugar to produce ethanol
    • "Carbon"-"Hydrated" = "a carbon with water added": CN-H2N-ON (commonly C6-H12-O6)
    • Glucose is the main carbohydrate
  • Proteins
  • Lipids
  • Naturally occurring enzymes
  • Sugar
  • Ethanol
  • Amino acids

Hops (spices)

Important attributes:

  • Contributes flavor to balance sugary malts
  • Essential oils
  • Flavor compounds come from the lupulin glands on the interior (looks like gold dust)

Yeast

Important attributes:

  • Converts sugar to ethanol (ethanol is anti-bacterial and thus a preservative)

Process

Malting

  • Enzymes are developed (and activated?)
  • Starts breaking down long-chain carbohydrates by activating enzymes to break down smaller sugars: disaccharides (maltose) & monosacharides (glucose)
  • Get hops wet
  • Apply heat to dry out hops
  • High heat results in chocolate flavors

Kilning

Mashing

  • Enzymes break down the starch in the grain into sugars
  • Finish breaking down long-chain (complex) carbohydrates and starches that was started during the malting process, and turning them into sugars.
  • Adding water to grain hydrolyzes sugars
  • Starch hydrolysis enzymes (alpha amylase & beta amylase)

Lautering

Boiling

  • Sterilizes, to ensure that only the desired yeast grows
  • Cool as quickly as possible to avoid contamination

Hopping

Fermentation

  • Adding yeast converts sugars into carbon dioxide and alcohol
  • Aerobic respiration
  • Anaerobic respiration

Second Fermentation

  • Lack of oxygen and ethanol both contribute to shelf life

Finishing (aging)

  • Allows different components of taste to either develop or be inhibited

Packaging

Chemical Concepts

Carbohydrates

  • Common forms for representing molecular structures:
    • 3D form used by organic chemists illustrates how the structure looks energetically in a solution (asyclic form)
    • Fischer projection is not as accurate in conveying the 3D form, but it gives you an easy way to draw the molecular structure
    • Lewis structure are the basic electron dot diagrams showing valence electrons in a molecule.
  • Hydroxide group is an Oxygen-Hydrogen (OH) pair in a structure
  • Cyclic form either goes up or down forming either an alpha (downward OH projection) or beta (horizontal OH projection) structure
  • Monosaccharide is two sugars together
  • Disaccharide is two sugars held together (such as maltose or sucrose) by a 1,4 alpha linkage (self-assessment says this should be 1,4 beta linkage)
  • Sucrose is a disaccharide composed of the monosaccharides glucose and fructose
  • Amylose is a long chain carbohydrate containing lots of glucose held together by 1,4 alpha linkages, which can be broken up by amylase (an enzyme)
  • Amylopectin: Has 1,6 alpha linkages in addition to 1,4 alpha linkages
  • Cellulose (from cell walls) has beta linkages and is a glucose (a monosaccharide) (self-assessment says this should be a polysaccharide)

Proteins

  • Important to health of the yeast
  • Comes from malt
  • Proteins are macro molecules made of long chains of small "building block" molecules called amino acid groups connected by amide and peptide bonds.
  • The "backbone" of a protein refers to the repeating nitrogen - alpha-carbon - carbonyl pattern (everything but the side chains).
  • Amide bond is a carboneal (sp?) connected to nitrogen
  • Acid moeity is a carboxylic acid
  • Amino acid
    • Contain an amino group on one side, and a carboxylate group on the other, with a substituted carbon, referred to as the alpha-carbon.
    • 20 are naturally occurring (such as Valine)
    • Valine is an amino acid that includes carboxylic acid, amino groups, and isopropyl groups and is important because it's used by yeast to eliminate dicytle (sp?)
    • In 19 of the 20 amino acids, the alpha-carbon is a chiral center, however, in glycine the 'R' group is simply a hydrogen, and thus the alpha-carbon is achiral.
  • Four levels of overall protein structure:
    • Primary structure: which amino acid is connected to which amino acid? The sequence of amino acids determine a protein's overall shape, function and properties.
    • Secondary structure: what are the interactions between amino acid groups? There are three important elements of secondary structure: alpha-helices, beta-sheets and loops. In a helix, the main chains follows a clockwise spiral, with side chains pointing out laterally. In a beta-sheet (or beta-strand), two protein chains are basically aligned in parallel. Loops are generally disordered segments of protein chain, but may be very ordered when in contact with a second protein or smaller organic compound. Helix and beta-sheet structures are held together by hydrogen-bonding between amide nitrogen on one amino acid, and carbonyl oxygen on another.
    • Tertiary structure: full three dimensional structure of a single protein molecule which is essential to the enzymatic activity, and gives the most information about a protein's function. Somehow related: alpha-Amylase is important in the breakdown of the carbohydrate Amylose. The three dimensional structure of a protein will also reveal the solubility in water, as hydrophobic residues tend to be on the inside, while hydrophillic residues exist on the exterior surface. When denaturing occurs, the hydrophobic structures are exposed to water and the protein loses it's solubility, forming solid precipitates.
    • Quaternary structure: how do multiple protein chains aggregate together as a "superstructure"? Many proteins consist of only one chain, and thus have no quaternary structure. When a protein consists of two identical subunits, they're called homodimers; when a protein consists of two non-identical subunits, they're called heterodimers.
  • beta-Amylase is important in breaking down carbohydrates
  • Proteins create proteinase (a group of enzymes capable of hydrolyzing proteins into amino acids)
  • Proteins create enzymes (essential to future processes)
  • In an enzyme, structure is essential
  • In an enzyme, temperature is essential
    • Denaturing occurs above the optimum temperature when the molecular bonds in a protein break down and the protein loses structure.

Lipids

  • Important to health of the yeast, mouthfeel, head retention, and flavor.
  • A good profile of lipids is important, or else:
    • Yeast may have problems creating their own lipids to form cell walls
    • Too many fatty acids from lipids may cause problems
  • Lipids come in two forms:
    • Complex lipids contain fatty acids such as triglycerides, waxes, and phospholipids
    • Simple lipids are simple hydrocarbon compounds such as steroids, prostoglandins and terpenes
  • Fatty acids have a polar head group (a Carboxylic acid group, O-OH), and a non-polar group
  • Fatty acids are important for foam retention
  • Phospholipids are similar to triglycerides, but have a phosphate group in the polar head group (with Choline) between Choline and the Glycerol Backbone, and are also important to cell walls.
  • Ergosterol is a common fungi or yeast
  • Terpenes that come from malts only contribute a minor amount of flavor, but those from hops provide a major flavor component (such a Humulene). They are simple lipids, I believe.

Commercial Brewhouse

  1. Mash kettle: some crushed malt & water @ 122 F and bring to boil
  2. Mash tun: rest of crushed malt & water @ 122 F and allow to rest ("protein rest")
  3. Decoction (the process of boiling down a compound in order to extract flavor): Transfer the contents of the mash kettle into the mash tun to kill enzymes and save dextrines (large carbohydrates which give body and small amount of sweetness).
  4. Lauter tun: Filter out the wort from the spent grain
  5. Brew kettle (copper) & hops: Move wort into brew kettle. (alpha acids released through melted lupulin glands produce characteristic beer bitterness). (alpha acids released through melted lupulin glands produce characteristic beer bitterness). The longer you boil them, the more are released, and the more bitter your beer will become.
  6. Whirlpool: allow hot material to settle out and decant.
  7. Fermentation: yeast is added. Krausening is the second fermentation process which smoothes out the taste of the beer and adds some sweetness.
  8. Aging: Moved to aging vessel. More hops may be added to restore hop flavor.
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