basic science for brewing - abgbrew.com + h2o Æ uptake of water and loss of crystalline structure...

Basic Science for Brewing

Carbohydrates Carbohydrate chemistry is a complex subject. It is, in fact, an entire field of study for scientists. As a brewer an understanding of the basics of what carbohydrates are and knowledge of a few of the reactions they participate in, in our breweries is very important. The name actually describes the molecule. Carbo for carbon and hydrate for the fact that the molecule consists of carbon associated with water or hydrated. They follow the same general structure which can be represented as Cx(H2O)y Simple Sugars (Monosaccharides) Examples include glucose, fructose, galactose, mannose, xylose and ribose

H2O + CO2 + sunlight Glucose + O2 photosynthesis Glucose H2O + CO2 + energy respiration Glucose alcohol + CO2 + flavor fermentation

.

The molecule can be represented as a straight open form or can be drawn as a closed ring structure below.

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Glucose exists as two separate isomers beta and alpha


Basic Science for Brewing Other isomers of the molecule C6H12O6 exist too

D-Allose D-Altrose D-Glucose D-Mannose

D-Gulose D-Idose D-Galactose D-Talose

Oligosaccharides Oligosaccharides are more complex polymers consisting of 2-11 monomers linked together. Examples include cellobiose, maltose, sucrose, lactose etc Maltose


Basic Science for Brewing Sucrose

Reducing sugars Since some sugars exist as an open chain and as a ring structure the bonds associated with the hemi acetal carbon are weak. This makes that portion of the molecule very reactive and capable of donating electrons causing other molecules to be reduced. O H

C C OH


Basic Science for Brewing Polysaccharides >11 monomers Most of the carbohydrate encountered in brewing raw materials is in the form of polysaccharides, consisting of 11 or more monosaccharides linked together. Starch



β glucan Large polymer found in barley endosperm cell walls. Consists of glucose β 1-4 (70%) chains interspersed with shorter β 1-3 ( 30%) chains.

Cellulose


Basic Science for Brewing Carbohydrates in beer provide • Fermentables • Sweetness • Viscosity • Mouthfeel Reactions of carbohydrates in brewing Gelatinization of starch Starch granule have a defined crystalline structure Granule + H2O uptake of water and loss of crystalline structure Increased viscosity Available for enzymic attack Gelatinization temperatures Barley 60-62 C Wheat 52-66 C Rice 61-82 C Maize 62-77 C Rye 49-61 C Oats 52-64 C Caramelization Heat a sugar in a low moisture environment and you begin to drive off the water molecules associated with each carbon in a dehydrating reaction

Cx(H2O)y Cx(H2O)y-1 The reaction is catalysed by heat and the presence of acids or salts and is a factor in malt kilning. When a water molecule is removed the resulting molecule forms double bonds between two carbons resulting in a different absorbtion of light and hence a darker color. Maillard Reaction Named after a French food scientist Maillard reactions involve reactions between i) a carbohydrate with a reducing group ii) free amino nitrogen


Basic Science for Brewing reducing sugar + amino acid an intermediate rearrangements (a reductone) degradations flavor + aroma color Descriptors for the flavors include toasty, biscuity, nutty, chocolatey, coffee, roasted, burnt, acrid while the colors produced range from light tan through all shades of brown to black Products produced through Maillard reactions include: • Chocolate • Maple syrup • Bread and bakery products • Coffee roasting • Cooked meats (methionine + glucose burnt turkey skin) When beer smells or tastes like these things its because they share many identical compounds due to Maillard reactions Reactions are facilitated by: pH 7.8 – 9.2 ie optimal in alkaline conditions High reducing sugar levels High temperature High FAN Low humidity (less than 30%) These ideal conditions more closely resemble the conditions found in the malt kiln or specialty malt roasting drum rather than the brewers kettle.


Basic Science for Brewing Proteins A protein is a polymer made of chains of amino acids with a specific structure and function. 20 amino acids commonly occur in nature, and are part of proteins in living systems. They share a common structure R = Reactive group R COO- (carboxylic group) Central C C H NH3

+ (amino group) All have the same backbone and different R groups Peptide bonds

A chain of amino acids 2-10 amino acids long is called a peptide. A chain 10-1000 long is a polypeptide and long chains over 1000 long are proteins. The chain of amino acids represents the protein’s primary structure. The primary sequence can fold to produce a secondary structure. The protein will have 1000’s of amino acids making up a molecule and fold so that they occupy less space.


Basic Science for Brewing Coil α helix

β pleat


Basic Science for Brewing Proteins are normally made up of a number of these structures. Determined by interactions of the constituent amino acids

The Structure of a protein gives the protein biological activity as well as functional properties. Biological activity • structure ie hair, fingernails, cells, muscles, tendons, cartillage • catalytic ie enzymes ( life cannot exist without them) • nutritional ie amino acids proteins Functional properties • Foams ie meringues, cappucino, beer foam • Emulsifiers Hydrophobic – fats and oils Protein Hydrophilic – water

Allows fat and oil to dissolve in water ie hop oils • Doughs ie gluten from wheat • Gels ie jello, collagen which consists of 3 α helixes wrapped around each other Isinglass (yeast removal) • Haze ie protein + polyphenol


Basic Science for Brewing The forces that hold a structure together are delicate and may be easily destroyed as the structure depends on “hydrogen bonds”, “ disulphite bond”, and “hydrophobic/philic bonds”. Proteins can be destabilized by a variety of agents. When a protein’s tertiary structure is destroyed it is denatured. 1. Heat Frying an egg is an irreversible reaction. The egg white is changed and

cannot be changed back

Heat Cool enzyme denatured enzyme does not renature 2. Physical

Beat an egg meringue Brew kettle 3. Chemical Add acids or bases curdling Cleaning a tank (solubilizing a protein) Enzymes Enymes are a type of protein Definition;

Protein: all rules that apply to proteins apply to enzymes Catalytic: any substance that lowers the activation energy of a chemical reaction without being changed by the reaction

Protein with catalytic properties due to its

power of specific activation Specific activation: do not catalyse reactions randomly


Basic Science for Brewing Activation energy

ie. Amylose maltose glucose CO2 + H2O This would happen eventually given enough time and heat energy but enzymes α amylase, β amylase and limit dextrinase allow it to happen more easily Enzyme activity Lock and key The enzyme is a specific shape and has an active site on it that is also specifically shaped. The substrate fits exactly into that shape as if it were a key fitting into a lock. The reaction occurs at that site and the products are released. Induced fit The enzyme still has active sites but the substrate causes a change in the enzyme shape to make the active site available and active.


Basic Science for Brewing pH Enzymes have a pH optimum for example, in a brewer’s mash the optimum is 5.1 – 5.4. This is because enzymes generally carry an electrical charge that is influenced by pH

Enzymes are active across a range of pH. We tend to quote the optimum pH for each enzyme where the reaction is most rapid Temperature Enzyme reactions increase rapidly as temperature increases. There’s a general rule that states that for every 10 degree Celcius rise in temperature the rate of a reaction doubles. The enzyme reaction approaches its maximum rate close to the point at which the protein generally becomes denatured. This results in a peak rate followed by a steep decline in activity as more of the enzyme is destroyed. The enzyme cannot be renatured on cooling so if the maximum temperature is exceeded then significant activity is lost.



Substrate concentration It follows that the more of the substrate for a given amount of enzyme is present the reaction will proceed more quickly. The enzyme will then become saturated and the reaction will slow to a constant rate




The maximum rate of the reaction is known as Vmax and ½ Vmax is known as Km or as the Michaelis Menton Constant

Product Inhibition The product of the reaction can chemically inhibits the enzyme. Enzyme cofactors Most enzymes also require other non-protein elements or compounds to be present in order to aid their action. The cofactor alone cannot catalyse the reaction. They fall into two categories: inorganic ions such a Zn2+, Mg2+, Mn 2+ , Fe2+, Cu2+, K+, Na+ or organic cofactors usually called coenzymes. These are often derived from vitamins, for example, coenzymeA, in the production of fatty acids, and in ester forming reactions. NAD+, and NADH (nicotinamine adenine dinucleotide), seen a lot in fermentation biochemistry. Proteins in Brewing Enzymes Amino acids yeast nutrients + fusel alcohols = flavor FAN Maillard reactions ( flavor and color) Proteins/polypeptides beer foam

beer haze (chill haze) mouthfeel

basic science for brewing - abgbrew.com + h2o Æ uptake of water and loss of crystalline structure...

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