The mashing

After we looked at the production of the malt in the last article, here we want to look at the further processing of the malt up to the fermentable liquid, the so-called word. Those who are not yet familiar with the basic production method of single malt whisky can find out more beforehand in this video and article.

The germinated and dried malt can only be stored for a limited time. The shelf life of the malt depends on the season in which you want to store it. In a dry summer, malt will naturally keep much longer than in a cold, rainy Scottish winter. This is because dry malt is not completely dry. The residual moisture it contains and the burst grain make it an ideal breeding ground for mould.

It is true that the malt silos of a distillery are sealed relatively airtight. But depending on the humidity, the contents of a malt silo can only be stored for between 4 and 12 weeks. Regardless of whether the malt is produced on the distillery's own malt floors or purchased from a large malting plant, it is transported into the malt silo either by old-fashioned scraper conveyors or modern transport screws or blower systems. Each malt silo is loaded from the top and emptied from the bottom. Gravity helps with emptying and this method of charging ensures that the malt is not overlapped but is also removed in the order in which it was filled. Only the order in which several silos are filled and emptied still needs to be taken into account so that the contents of a single silo do not overlap.

Removal takes place via simple taps and once again closed conveyors. The next station is not the malt mill, but first a mechanical screening machine.

Here, the last little stones and unmalted hard grains are removed from the malt stream with the help of an oscillating system and gravity. It is amazing what combine harvesters cannot do and how many stones are still in the malt at the end.

Then, finally, the malt is ground. And what is used ... quite normal grain mills, as we know them from our domestic grain mills. The similarity and even the red colour are frighteningly similar to our German mills. It seems as if there has been a standardisation or copying of the designs centuries ago. There are different types of mills in the whisky industry. A hammer mill is mostly used for corn, wheat and rye. Hammer mills have rectangular plates of hardened steel attached to an axle. The plates rotate around the axle at high speed inside the grinding chamber. The hammers hurl the grain towards the plates lining the mill's housing, which crushes the grain. In roller mills , the grain is pushed between stacked pairs of rollers, where it is shattered by the strong pressure.

The smooth rollers can rotate at different speeds to increase the pushing force. The slow speeds mean that the grain is not heated and there is no associated loss of moisture. Roller mills are used as standard for malted barley. Well-known brands include the 'Porteus Mill' (as used by Craigellachie) or the 'Bobby Mill' (as used by Ardbeg).

For grinding the malt, however, these mills are set with larger gaps. Instead of producing a fine flour, these roller mills produce a coarse grist. It is fine enough to break the grain completely but not as fine as flour, so that in the later liquid part of the process the sieves and the other equipment do not stick together.

The coarsely ground grain, which the Scots call grist, still consists mainly of starch. The malting process has created the enzyme amylase in the grain, which now does its work in a resting phase during mashing and splits the starch into different sugars.

With the advent of mechanisation, the mash tuns were made of cast-iron segments (see above) that were bolted together at their edges. To simplify stirring, a mechanical, metal stirrer with a central bevel gear drive was installed. This not only accelerated the sugar dissolving process, but also significantly improved its efficiency. Less sugar remained in the husks of the grain and the whisky became cheaper.

To optimally dissolve the malt sugar from the grist, you have to stir the mash in the Mash Tun for several tens of minutes. In the past, a lot of water evaporated during this time and the temperature in the mash tun continued to drop with the water vapour, which further worsened the dissolving process. It was only in the last century, with rising energy prices, that almost all mash tuns were fitted with a lid made of sheet metal (e.g. copper) to limit the loss of energy.

Today, a multi-stage dissolving process for the mash tuns of all distilleries has become established. The mash tun is filled with a few tonnes of grist and hot water from the company's own boiler is added via the mash mixer. The ratio of grist to water is about 1:4, resulting in a hot porridge-like porridge. The first water filling is not quite as hot. The temperature of this first water is around 60 to 70 degrees Celsius. The first filling also has another special feature, which we explain at the end of this section. This first water is left in the Mash Tun for about an hour with slow stirring before it is pumped out.

Pumping out is much slower than filling. With modern, shallow Lauter Tuns, the sugar water can be drained through a fine filter screen within an hour without getting any shell residues into the underback, the collection tank. Old, tall mash tuns often require extremely slow draining over up to 6 hours to obtain shell-free water for fermentation.

When pumping out, heat is extracted from the sugar water, which is now called word, via a heat exchanger and cooled down to around 20 degrees Celsius for later fermentation. This energy recovered in this way is used again to heat the second water. Since a good part of the sugar is already dissolved from the grist, the second filling is heated to higher temperatures above 70 degrees Celsius to intensify the dissolving process. Almost always, an even hotter third filling is made at 80 to 90 degrees and even in rare cases a fourth infusion is used. Common to all distilleries is the peculiarity of the last water. Since it contains only a little sugar, it is reused as the first water for the new filling without being reheated.

The modern Lauter Tuns(lauter tuns), which are being used more and more often, are designed for speed as well as sheer size. The low height and the sieves at the bottom allow the sugar water to be drained over the bottom into the underback far more quickly than is possible with old, traditional mash tuns. With them, you have to allow a certain resting time after stirring so that the bowls float up on the sugar water and you can slowly drain the clarified sugar water downwards with a steady hand. The yield of the modern Lauter Tuns has also been improved, as large, circling arms with attached knives allow for much better mixing of the grist with hot, dissolving water. Finally, the shape of the Mash Tun bottom is also important if you want to drain not only the sugar water after the last filling but also the bowl remains afterwards. A curved bottom makes it easier to dispose of the non-soluble remains of the grain.

These leftover shells, which the Scots call draff, contain large amounts of proteins, trace elements and minerals that are used as concentrated feed for animal breeding. The high water content makes draff very heavy and difficult to transport. For this reason, the water is removed from it in large evaporation plants. The town of Rothes, for example, has its own evaporation plant to which all the local distilleries transport their draff.

However, some distilleries (e.g. Glenfarclas and Mannochmore/Glenlossie) have taken care of an evaporation plant themselves in the past. In this way, the animal feed can be taken directly in bags from neighbouring farmers. This partnership between farmers and distillers is centuries old and was described by Alfred Barnard in 1887 for 35 of the distilleries he visited at the time.

After the sugar has been released from the malt by mashing, the word must be fermented in wash backs. The resulting "beer" can then be distilled. Learn more about the conversion of sugar into alcohol in the following article. Read more about distilling in this article.