MALTING. (Steeping, Germination and Kilning)
Since 1972, ‘maltsters’, companies who specialise in malting barley, produce the malt to our required specification. The Pagoda roof, from the old kiln, now takes pride of place over the entrance to the Visitors Centre. The barley is usually grown in Scotland, and often in the local area of Moray; prime barley growing country.
Newly harvested barley, with a moisture content of 11 - 12%, is steeped (soaked) in water and germinated to start a complex chemical reaction, which is then gradually halted by increasing the temperature during kilning.
The barley used to produce the distillers’ malt is Hordeum distichon, with varieties such as Chariot and Optic popular for their low nitrogen content (below 1.6) and a 98% germination rate.
Steeping the barley is probably the most important part of the malting process. If it is performed effectively then the next two stages, germination and kilning, are routine. The objective of steeping is to achieve a moisture content of 46% with a strong uniform growth. Steeped in a saladin box (steeping, germination and kilning vessel) at 16 deg. C.
The barley is encouraged to grow and enzymes are produced. These enzymes are vital for converting the starch into fermentable sugars.
Temperate, humidified air is blown through the germinating barley. The volume of air is used to regulate the temperature, whilst humidification minimises moisture loss to 3-4%. The moisture content of this ‘green malt’ has an effect on the all important enzyme development.
As the barley grows, the plant hormone gibberellic acid induces the synthesis of hydrolytic enzymes. Enzymic hydrolysis of proteins and beta-glucans in the starchy endosperm, transforms the hard endosperm of the barley into the soft (friable) endosperm of the malted barley, which can easily be ground into ‘grist’ during the milling process.
The barley is also turned regularly to prevent the roots matting together, and to release any carbon dioxide.
Kilning (Free Drying, Middle or Falling Rate Phase, Curing)
Over a 24 – 48 hour period the ‘green malt’ is dried carefully, to halt germination, and to reduce the moisture content from 43% to the required 4.5%. It is vital to preserve the enzymes, released through germination, which enable the final conversion of starch to soluble, fermentable sugar, to be completed during mashing.
During the first stage of Kilning, moisture is freely available at the surface of the barley. The drying rate is dependent on the air-on temperature and air flow, which varies between 45 – 75 deg. C. After this phase, the moisture content will be 10-20%.
Middle or Falling Rate Phase
Rate of drying is limited by the ability of moisture to move from the inside of the barley to the surface, where it can evaporate. Temperature during this phase varies from 65 – 75 deg. C. with a final moisture content of 5%.
The temperature is increased to 70 – 75 deg. C for distillers’ malt. The final flavour and colour of the malt is established and the final moisture content will be below 4.5%. Malted barley for distilling will not receive a true cure, only sufficient heat to reduce the moisture content, whilst retaining as much enzyme activity as possible.
During kilning complex chemical reactions take place. Amino acids and sugars are degraded, or react together to produce distinctive roasted, malty flavours in the barley.
Finally, malted barley contains more endosperm degrading enzymes than barley, more soluble proteins, amino acids and more colour compounds. This enables greater hot water extraction of malt sugars and amino acids during mashing, thus producing a greater yield of ethanol during fermentation.
The malted barley is delivered to Glenfarclas Distillery and stored in the ‘malt intake’, which has 11 hoppers, with a capacity of 330 tonnes.