A view to a kiln

A view to a kiln

Kilning might seem to be a standard practice,but it has a large bearing on the whisky-making process. Ian Wisniewski reports

Production | 01 Jun 2006 | Issue 56 | By Ian Wisniewski

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Kilning may seem an entirely practical function, in order to dry the barley once it has germinated. However, maintaining a consistent regime requires considerable skill, and not only to optimise the yield of alcohol. Kilning also develops the character of the malt, while peating adds an additional range of phenolics.As part of the malting process, kilning follows steeping and germination, which provides the distiller with direct access to the grain’s starch content. Steeping sees the barley hydrated in steeps (vessels) to enable germination.Starch within the endosperm (main interior section) serves as a food source, enabling the grain to produce the energy required to develop roots and an acrospire (shoot).As the starch is initially enclosed within proteinlined cell walls, the embryo needs to dismantle these walls to access the starch. Enzymes are also produced during germination, which are vital for the conversion of starch into fermentable sugars during mashing.Once the starch has been ‘liberated,’ further growth is arrested by kilning (applying heat).Otherwise if the grain were to use starch to continue growing, less starch would be available for the distiller, meaning a reduced yield of alcohol.The moisture level of the grain is typically around 45 per cent at the beginning of kilning, with an initial temperature limited to around 50 degrees Centigrade. Temperature is a crucial consideration when drying the grain, to render the enzymes temporarily inactive enabling the grain to be stored safely prior to milling.Hot water subsequently re-activates the enzymes during mashing. However, too high a temperature would render the enzymes permanently inactive, and the grain would become redundant.The initial phase of kilning essentially dries the surface moisture of the grain, which means the temperature of the actual grain rises slowly.An important stage known as the ‘break point,’ is when the surface moisture has been driven off. After reaching the break point the temperature can gradually be increased to a peak of around 75 degrees centigrade.Raising the temperature reflects certain pragmatic concerns, such as keeping to a production schedule. Using the most appropriate amount of energy to complete kilning in the most cost-effective manner (energy being an expensive element) is another factor.However, while a higher temperature means a shorter drying time, the higher the temperature the greater the risk of damaging enzymes.The malt’s flavour profile essentially develops after the break point, with the original starchy, cereal character yielding a range of sweeter, biscuity, malty notes, as the moisture level is brought down to around 4.5 to five per cent.If the malt is being peated, an important factor is that moisture promotes the absorption of smoke, essentially by the husk. As the surface dries, it becomes progressively harder for the grain to absorb smoke, with far less absorption after the break point.The majority of the industry is catered for by commercial maltsters. Established in the 19th century, commercial maltsters only emerged as major players during the 1960s-70s. That’s when numerous distilleries added mashtuns, washbacks and stills to increase production capacity. But rather actually closed.Malting floors weren’t considered financially viable, compared to commercial maltsters equipped with modern technology, and offering more consistent quality at a more competitive price.Undertaking steeping, germination, kilning and peating (as required), commercial maltsters work to a specification agreed with a distillery. This includes the PSY (Predictable Spirit Yield), which distillers subsequently use to benchmark the actual spirit yield when the malt is distilled.“The quality of the barley has to be taken into account, and distillers may have set their specification depending on the crop quality each year,” says Mark Kinsman, of commercial maltsters Baird’s Malt.“Some distillers specify a variety, but they also have to consider new ones being introduced by breeders.“The industry is working on three main varieties, Optic, Chalice and Braemar, with a fourth, Oxbridge now undergoing commercial assessment.“Some distillers have niche requirements and this malting barley can be contract grown to meet these needs. Different varieties can have a different grain size, which can affect the steeping regime for example.” With most modern kilns you’re looking at a 24 hour cycle, whether the malt is unpeated or peated, and computer operated, though also monitored by an operator, with alarm systems included just in case.“All kilns are indirectly fired, using air that is heated by being drawn through a ‘radiator,’ which can be heated by hot water or steam.” A ‘combined’ approach can also be used to undertake two or more of the separate stages of malting, such as germination and kilning, within one vessel. Alternatively, combined Steep, Germination & Kiln Vessels are used for example by Bairds’ Inverness maltings.Conceived in the late 1960s, this offers a flexible system that includes the option of peating to various levels, and typically takes eight days.Among the few distilleries retaining malting floors and kilning on-site are Bowmore, The Balvenie, Highland Park, Laphroaig and Springbank, where it’s a ‘hands on’ rather than automated process.Controlling the kiln, and the peating regime, entails various parameters, not least of which is the weather.“A strong wind can help draw smoke through the bed, but you have to make sure that your fire is not burning too fast, and check the peat fire more often,” says Bowmore’s Ian McPherson.Laphroaig’s John Campbell adds: “An east wind is not as good for us, it doesn’t draw so well, and so the smoke doesn’t go through anywhere near as smoothly.” As a traditional kiln doesn’t have any hightech accessories, it’s a case of relying on what there is.“We have two doors on the top and two on the bottom, and the opening and closing of these doors affects the draft.“The side doors also give more ventilation,” says John Campbell.Needless to say, operating a kiln requires one particular asset.“It’s all done by men not machines, and our guys have been here for at least 15 years, easily. It’s experience and savvy. Nothing beats experience,” adds Ian McPherson.John Campbell concurs: “The experience of the operator is crucial and it’s the hardest shift to learn at Laphroaig, as conditions can often change throughout a shift, as well as over the whole year.” Apart from the weather, knowing when, how much, and what type of peat to add, in order to maintain a consistent regime that results in the same phenolic influence, is obviously vital.The more fibrous top layer of peat for example provides more smoke, but is more reluctant to burn than darker, underlying layers of peat which produce more heat.Very dry peat gives heat but not much smoke, and so contributes a relatively lower level of phenolics.Adding smaller blocks of drier peat and crumbly debris, known as ‘caff’ or ‘peat fines,’ can help impede air flow and so produce more smoke, as well as plugging any gaps where a flame may try to break through.This type of peat can also be hosed (being very dry it holds water well), and used in its rehydrated form to help ‘cool’ the fire (without of course extinguishing it) and promote smoke.“The skill and dedication of the kilnsman has a huge part to play, it’s a balancing act to get the key components together, fire that produces smoke and very little flame.“There’s no automatic control, it’s a guy with a shovel and some peat,” says Highland Park’s Russell Anderson.Peating levels are measured as parts per million phenol (ppm), with a lightly peated malt typically around 1-10 ppm, a medium level around 10-30 ppm, and 30-50 ppm for a heavily peated malt.“From a scientific point of view we measure different phenols within the malt and new make spirit. In new make spirit what I’m looking for is a lovely balance between heather honey and estery sweetness and a peat, smokey, ashy note. Peating is absolutely critical to the quality of the new make spirit,” says Russell Anderson.Whoever malts the barley it is subsequently ‘rested’ in sealed bins for several weeks, which is an important stage.As the heat of kilning ‘pushes’ remaining moisture to the edges of the grain, the resting period allows this moisture to gradually extend back, and be evenly distributed throughout the grains. This ensures that milling is more even, promoting fermentability and consistency.
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