Germination Of Barley
Barley germination
- During germination a new barley plant is produced from the kernel
- To form the new plant the barley needs a large amount of energy & building materials which must be produced by respiration & other metabolic processes
- Endosperm is degraded by enzymes which are formed during germination
- The production of enzyme is the main purpose of malting
- These enzymes are essential for the breaking down of large molecules during mashing
- To avoid of material the enzymic degradation process are restricted during malting
Process occurring during germination
a. Growth process
The germinating kernel develops rootlets & acrospire
1. Rootlets
- Be about 1.5 times the corn length for Pilsner malt
- Be about twice the corn length for dark malt
- To keep rootlet loss low, germination is performed at the lowest temperature for the shortest time
2. Acrospire
- The development of the acrospire & the progress of modification of the kernel run approximately parallel to on another
b. Enzyme formation
- Enzymes are already present in abundance in barley
- They are set free of formed in ever increasing amounts during germination
- Enzyme complexes which are contain in barley & malt ;
1. Starch degradation enzymes (alpha & beta-amylase)
alpha-amylase
- Is not detectable in ungerminated barley
- Is produced on the 2nd to 4th days of germination
beta-amylase
- Is present in large amounts in ungerminated barley
- After an initial decrease the amount of beta-amylase increase on the 2nd & 3rd day of germination
- Aeration in the first germination phase is important for the production of beta-amylase
- The amount of alpha & beta-amylase formation depends on
-Variety
– Large kernel from more amylase
– A higher water content increase the amylase
– Cold germination gives the highest amylase
2. Cytolytic enzymes (beta-glucanases & cytase)
- Is produced on the 3rd to 4th days of germination
- Protein degradation enzymes (proteolytic enzymes or proteases)
- Is produced on the 3rd to 4th days of germination
- Phosphoric acid splitting enzymes (phosphatases)
Enzymes are produced as a result of the action of hormones which are distributed with the penetration of water from the scutellum along the aleurone layer & which cause the release & formation of enzymes. These hormones consist of gibberellic acid, they cause the release of amino acids & the production of enzymes. First beta-glucanase, then alpha-amylase & protease, beta-amylase is formed or released in the endosperm.
c. Change of storage materials during germination
Modification is degradation process which lead to the production of low molecullar weight products form high molecullar weight compounds.
1. Solubilisation & degradation of beta-glucans
- The endosperm cell walls consist predominantly of a framework of hemicellulose & protein
- During germination cell walls are broken down by the cytase enzyme complex, this includes hemicellulase & beta-glucanases
- As a result of this cytolytic degradation a part is cleared for the other enzymes into the endosperm & so enzymic degradation can proceed more easily
2. Starch breakdown
- For respiration the starch must be transformed into transportable sugar & supplied to the seedling
- As a result of the respiration the starch is lost
- To keep the respiration loss as low as possible, germination is performed for as short time & at as low temperature
3. Protein breakdown
- During germination 35-40% of the protein is degraded to soluble material
4. Dimethyl sulphide (DMS) formation during germination
- Is a volatile sulphur compound which gives beer a flavour referred to as “cabbagey” or “cooked vegetable”
Germination regulators
- By the addition of specific substances it is possible to interfere with the mechanisms of metabolism to obtain accelerating or retarding effects
- These substance are called growth regulators & are divided into;
1. Stimulators
- The most widely used stimulator is gibberellic acid which product of Fusarium moniliforme
- The amount of gibberellic acid added is 0.03 to 0.08g per ton of barley
- The advantages of using gibberellic acid are;
- A shortening of germination time by 2 days
- An increase in product yield of about 1%
- An increase in extract yield of about 1%
- A shortening of dormancy of the barley
2. Inhibitors
- By addition of potassium bromate, proteolysis can be inhibited
Conclusions about how to perform germination
- Germination is intensive life process which can occur only in the presence of sufficient water
- The steeping goods must be provide with sufficient oxygen
- Respiration cause the temperature to rise. For Pilsner malt 17 to 18 oC & dark malt 23 to 25 oC
- For proper performance of germination it is necessary to control the water content, the aeration & the temperature
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