Learn
Table of Contents:
Barley
> Chemical Composition
>> Moisture Content
The Moisture Content of Barley is between 11-20%. All analyses of barley are based on dry weight, and expressed on a moisture free basis. The higher the moisture content the greater chance for mold growth, and the lower your extract yields will be. You want to store barley under 13%, but start the drying process around 45%.
>> Starch
Starch has the chemical formula: ( C6H10O5 )n. A complex carbohydrate, a polyose. It is easily hydrolyzed into glucose, dextrins, and maltose. Starch is stored in the roots, tubers, and seeds of plants. Amylolytic enzymes convert starch to dextrins and maltose. Starch composes 55-65% of the dry weight of barley. Maltose is broken down during fermentation to CO2, but dextrins, which are non-fermentable by brewer’s yeast, pass unchanged into the beer. An iodine test is usually done to check when saccharification is complete.
>> Nitrogen and Protein
The term “Total Nitrogen” covers the whole of the organic nitrogenous material of barley. Proteins of high molecular weight and complex molecular structure form the bulk of the organic nitrogen, but barley also contains small amounts of protein breakdown products, and it is therefore better to speak of “nitrogenous matter” than merely “proteins.” The protein content of barley varies between 9 and 11%. Nitrogen is made up of different factions and each faction plays an important role. The less complex substances are assimilated by yeast during fermentation, but the more complex proteins are unable to diffuse through the cell wall of the yeast. Though, some yeast do not fully metabolize the assimilated nitrogen, and a residue can be left that dangers the stability of the beer, and may lead to biological infection. Head retention and mellowness of palate are closely connected with protein content, but after a variable period of shelf-life, proteins can appear as a visible haze in the bottle.
The complex molecule of any protein is formed by the union of a number of different amino acids. the simplest amino acid is a alpha-amino-acetic acid of glycine:
Amino acids posses the property of uniting with one another by condensation of the carboxyl group (–COOH) of one acid with the amino group (NH2) of the same, or another acid, with the loss of a molecule of water, to an almost infinite extent. This compound is called a peptide.
Amino acids are substances in which one or more of the hydrogen atoms (other then the carboxyl hydrogen) are replaced by the amino group (NH2).
As highlighted in red, the grouping of the OH from the –COOH with one H from –NH2 is called a peptide linkage. When three molecules unite, the result is called a tripeptide, and the series has been extended so that many amino acids are present; these products being termed polypeptides, and have the general formula:
where R1, R2, R3 . . . represent amino acid residues. These polypeptides will always contain a free amino group (–NH2) and a free carboxyl group (–COOH).
Natural proteins are hydrolyzed to amino acids and other intermediate products by proteolytic enzymes. Many proteins contain sulphur in the molecule. The sulphur is present in sulphydryl groups (–SH) which are readily oxidized in solution by activated oxygen to the dithiol linkage, –S–S–, by loss of hydrogen, bridges, and even by linkage of the two or more protein molecules. Oxidation of these sulphydryl groups of proteins is considered the main cause of colloidal haze in bottled beer.
Three classifications of proteins: Simple, Derived, and Conjugated
- Simple Proteins: Are substances of high molecular weight (20,000 – 300,000), and when heated in solution the molecules are denatured and flocculate, and are also precipitated by salts.
- Derived Proteins: Intermediate products of hydrolysis between proteins and amino acids. Although still large, these products are soluble in water, not coagulated by heat, and not precipitated by salts.
- Conjugated Proteins: All contain prosthetic group in the molecule, i.e. a radical which is not an amino acid in character. The glycoproteins, for example, contain prosthetic groups which include one or more carbohydrate radicals.
During germination complex proteins in barley are hydrolyzed by proteolytic enzymes secreted by the embryo into amino acids and simple peptides which feed the plant before it can get nitrogen from the soil
During malting only these complex proteins are hydrolyzed, leaving a significant amount of protein stored in the endosperm, which is then passed to the wort through mashing.
During kilning the embryo is killed.
Boiling wort denatures and coagulates the proteins which becomes cold break / hot break.
During Fermentation the yeast draws nitrogen supplies from the amino acids and simple peptides dissolved in the wort, but not all is used, and some passes into the beer.
Precipitation of proteins after boil should be complete or else you will experience a protein haze in the finished beer.
Presence of proteoses, or water-soluble compounds that are produced by the hydrolytic breakdown of proteins short of the amino acid stage, and peptones (a derived protein, which may be produced by hydrolysis of a native protein with an acid or enzyme) are good for mouthfeel and head retention.
Too much nitrogen in wort can leave nitrogen left over for bacteria to feed on.
Amphoteric electrolytes are compounds which have the properties of both an acid and a base. A molecule with both a –NH (basic amino group) and –COOH (acidic carboxyl group).
Since proteins are amphoteric electrolytes, they function as bases in the presence of acids, and a acids in the presence of bases.
Proteins belong to the class of substances known as colloids and their stability in solution depends upon the nature of the charges carried on the molecule. Colloids carry either a + or – electric charge and the stability of a colloidal solution largely depends on this fact.
A method for determining the isoelectric point of a protein is to ascertain the pH at which the first visible sign of precipitation can be detected with a precipitating agent.
Dextrins, which are highly hydrated colloids, protect the proteins in beer.
Four groups of proteins in barley based on solubility in solvents
- Albumin: Protein soluble in water and a dilute saline solution.
- Globulin: Protein soluble in a dilute saline solution, but insoluble in pure water.
- Prolamin: Protein soluble in 60-75% ethanol.
- Glutelin: Protein soluble in weak alkali.
Boiling assists in separating albumin proteins.
Globulins are heat resistant and end up in the wort to potentially cause protein haze.
Albumin plays an important part in head retention, but also contain beta-amylase portion of grain.
Beta-Globulin fragments formed during the boil combine with tannin from the hops to form chill haze.
Protein haze forms at levels of 5-50 parts per million. Protein haze is also caused by a complex mixture of tannins, mineral salts, and proteins.
Routine laboratory tests performed on Barley, Malt, Wort, and Beer
- Barley: Total Nitrogen
- Malt: Total Nitrogen, Soluble Nitrogen, and occasionally Heat Coagulable nitrogen and formol nitrogen.
- Wort: Permanently Soluble Nitrogen, and occasionally formol nitrogen.
- Beer: Permanently Soluble Nitrogen, and occasionally formol nitrogen.
>> Carbohydrates
Examples of carbohydrates are starch, cellulose, hemicelluloses, gums, pectins, pentosans, and sugars.
- Cellulose makes up a large part of the husk, and provides a filter for the grain bed during mash.
- Hemicelluloses maintain the structure of the cell wall, and can be hydrolyzed into sugars.
- Pectins are also a component of the cell wall, but only present in small quantities in barley, and don’t contribute to much of anything.
- During malting, there is a progressive decrease in viscosity of extract which is attributed to the hydrolysis of Gums.
- Also during malting, Pentosans are liberated by the hydrolysis of hemicelluloses, gums, and pectins. The pentosans, can in turn be hydrolyzed to free pentoses, and being unfermentable sugars, pass into the beer unchanged.
- A small amount of sugars are in resting barley. Examples are sucrose, maltose, raffinose, and the reducing hexoses glucose and fructose.
- Tannin: cause acrid flavor–astringent. Found in husks.
- Phytin: Found in husks and endosperm. Phytin are hydrolyzed into phosphates which are again essential for regulating pH and fermentation.
>> Lipids
Lipids compose about 2-3% of the total chemical composition. Lipids are fatty material in barley, usually left in the mash, but some lipid material passes to the wort.
>> Ash
Ash composes 2-3% of the total composition as well. Ash is made up of mostly potassium, phosphate, and silica, but also contains some magnesium, calcium, sodium, iron, and sulphur. Phosphates from ash are essential for fermentation.
>> Misc. Non-Nitrogenous Material
>> Enzymes
Enzymes are usually notated by the suffix –ase. Enzymes are complex organic compounds that serve as catalysts for chemical reactions. They play a role in hydrolyzing complex organic molecules such as proteins and polysaccharides into simpler substances to be used in active metabolism. Each enzyme is highly specific in its role for which it catalyzes. The substance upon which a enzyme acts is called a substrate. Certain complex substances, starch and proteins, can only be completely hydrolyzed in stages by a series of enzymes. A rise in temperature of a reaction will also increase the rate of the reaction, but a rise in temperature will also have a destructive effect on the enzyme.
At malting, the enzymes attack food stores in the endosperm to be used for various metabolic needs. The malster arrests germination when necessary enzyme systems are fully developed. At mashing, these reserve food supplies in the endosperm are hydrolyzed and pass into solution in the wort, and then are attacked by the yeast to make beer.
Hops
> Description
Humulus Lupulus. A dioecious plant–meaning male and female inflorescences are carried on separate plants. The female inflorescences (strobilus or cone) are used in brewing. The bitter resins and essential oils are secreted at the base of the female flower. Hops are a perennial plant. Epidermal hairs are the lupulin glands that secrete the resins and oils on the base of the bract of the flower and look like a yellow powder.
> Chemical Composition
>> Moisture Content
Freshly picked cones have a moisture content of around 75%, and that must be reduced to 12-13% during the drying process or you will risk oxidation. The drying temperature must be no greater than 50 degrees Celsius.
>> Resins
Humulone and Lupulone which are secreted by the lupulin glands. Alpha-acid is humulone C21H30O5 and beta-acid is lupulone C26H38O4. Humulone is actually humulone, cohumulone, and adhumulone. Lupulone is actually lupulone, colupulone, and there is evidence for adlupulone as well. The humulone complex is the primary bitter principle in hops, and also has a higher preservative value than lupulone. There is usually around 2-8% humulone in hops, but can go as high as 17%. Stored hops can develop soft lupulone resins which can make up for some of the bittering loss from the depletion of humulone due to oxidation. Hops usually contain between 6-8% lupulone.
>> Essential Oils
Besides resins, lupulone secretes these essential oils, which are responsible for hop aroma. The average content is 0.4%. The oils are myrcene C10H16 and sesquiterpene humulene C15H24. Oils are volatile in steam, and largely lost when boiled in wort, which is why you need to dry hop to get aroma or use excessive late hopping in the kettle.
>> Tannin
Hops contain 2-5% tannins. The chemical nature of the tannins differs widely for each species of hops. When oxidized, hop tannin is converted into reddish-brown phlobaphene, which regularly combines with proteins to make insoluble complexes. Both tannin and phlobaphene help in precipitation of protein in boiling wort and finished beer. Tannin is found in the bracts and strig of the cones.
>> Misc. Compounds
Hops have a cellulose content that is insoluble and remains in the kettle. They also contain around 12% pectin. There is 15-20% nitrogenous matter which are mostly dissolved during the boil as well. A small amount of glucose and fructose is found in the cone. Sulphur Dioxide is found in dried hops because sulphur is burned in the kiln to preserve the green color and it may also help with storage. There is usually no more than 0.3% SO2.
> Evauluation
>> External Characteristics
You can evaluate hops based on the following characteristics: (1) Spring or elasticity, (2) soundness or how tight the cone is, (3) impurities or no stems, seeds or leaves, (4) uniformity, (5) size and density of cones (short bracts are better), (6) lupulin or the yellow powder, (7) seeds, (8) aroma, (9) color should be green to slightly yellow, and (10) no faults such as brown spots caused by wind damage or fungal infection.
>> Chemical Analysis
Moisture Content
Is determined in the same was as for barley; by drying a weighed sample for 1 hour at 105 degrees Celsius in an oven.
Resins
Humulone, alpha-soft resins, and the beta fraction are analyzed. Hard resins are not important in brewing and should not exceed 10 – 12%. Resin content can vary from year to year, crop to crop, and even with the state of the maturity of the cones.
Bitter Value
Humulone or the alpha fraction imparts 9 times more bittering than the beta fraction, and hard resins impart no bittering power. Storage of hops can oxidize the beta fraction and increase its bittering power.
Preservative value
The preservative value of humulone is 3x as great as that of the beta fraction, and can be determined using the following formula:
>> Storage
Hops should be stored at 0 degrees Celsius, and compressed into tight pockets or metal cylinders with limited exposure to the air. At 0 degrees C, hops should retain their quality for 2 years or more.
>> Hop Extract
Hop extracts are made by dissolving out the resins, tannin, and essential oils with various solvents.
Water
> Chemical Composition
Sources
A Textbook of Brewing, Volume I, by Jean De Clerck, translated by Kathleen Barton-Wright, 1994 reprinting.