Understanding Whisky Production · Unit 2: Raw Materials

Chapter 2: Cereals in Whisky Distilling: Barley, Maize, Wheat, and Rye

The chemistry of cereal starches, gelatinisation temperatures, nitrogen content, and how grain selection shapes spirit yield and flavour.

From an agricultural point of view, a grain of cereal is a tiny, armoured survival pod containing a dense parcel of starch intended to feed an embryonic seedling. From a distiller’s point of view, it is an alcoholic drink that has not quite reached its potential yet.

The central obstacle is that starch consists of thousands of glucose units locked into tightly wound polymers: linear amylose and branched amylopectin. Unravelling them requires heat and water to swell the granules (gelatinisation), after which enzymes can get to work. Different grains strike different thermodynamic bargains: barley gelatinises comfortably below 65°C, while maize and wheat demand pressure-cooking above 75°C to surrender their sugars. Without which the yeast would, upon introduction into the washback, sit smiling politely, utterly confused and then slowly starve to death.

Cereals and their Analytical Requirements

We can use many starch sources to produce fermentable sugars. We will explore the most common cereals used in the distilling industry. We generally determine whether they are a good source or not, by looking at the certificate of analysis (CoA).

Why do we use cereals and not just regular table sugar?

Other than providing starch, cereals also contribute unique flavours to the product. Barley, or more specifically malted barley, also contributes the enzymes that break down the starch to fermentable sugars. Before we continue, we must understand what an enzyme is.

An enzyme is a catalyst of biological origin, usually a specific protein in our case from malt or yeast, that helps chemical reactions to occur more rapidly. The fermentation of sugar to alcohol is carried out by a succession of enzymatic reactions within the yeast cells. Barley produces specific enzymes that break down starch into sugars. The main enzymes are α-amylase, β-amylase and limit dextrinase. The symbol for alpha is α and the symbol for beta is β.

If a distillery is to produce any alcohol at all, it must first lay hands on cereal starch. In an ideal world, starch would simply materialise at the distillery gates in neat, obedient, perfectly soluble parcels. In the real world, sourcing grain requires balancing agricultural realities, industrial chemistry, transport logistics, and the uncompromising vigilance of the excise authorities.

Before a single grain lorry pulls into the yard, a distillery must weigh several competing factors:

• Product Identity and Legislation: Distillers rarely have total freedom of choice. The law usually gets there first. If a distillery intends to produce Scotch single malt, statutory regulations forbid using anything other than 100% malted barley, mashed without external enzymes. A bourbon distillery must legally ensure its grain bill contains at least 51% maize. Grain distilleries, by contrast, have greater latitude to shop for whichever cereal yields the highest volume of fermentable sugars for the lowest outlay.

• Potential Alcohol Yield: Distilleries are not really buying cereals; they are buying starch packages that can be coaxed into sugar. Grains with higher starch content yield more litres of pure alcohol (LPA) per tonne. Every percentage point of unfermentable material or unwanted protein represents energy spent cooking something that will never become whisky.

• Supply Security and the Harvest Dilemma: Agriculture operates on seasonal whims; distilleries operate on demanding production schedules. Cereals are harvested over a few frantic weeks in late summer, but the stills run year-round. A distillery must therefore either build immense grain silos to shelter an entire year’s supply of cereal from damp and rodents, or enter long-term contracts with commercial maltsters who take on the logistical headache of storing and conditioning the grain on their behalf.

• Handling and Physical Logistics: Moving hundreds of tonnes of dry grain is an exercise in applied mechanical friction. While buying cereal in one-tonne bulk tote bags might look economical on an invoice, it rapidly ceases to be a bargain if the distillery lacks a forklift and has to pay a team of exhausted operators to manhandle them across the yard. Large operations invest in pneumatic blowers and grain augers that gulp grain directly from bulk tipping lorries into overhead hoppers.

• Raw Economics vs. Processing Ease: Unprocessed raw grain is significantly cheaper than malted barley. However, raw cereals demand extra energy, specialised pressure cookers, and gelatinisation vessels to break down their stubborn starches. Unless a distillery already possesses the heavy machinery and steam capacity to cook unmalted grains, buying raw cereal to “save money” simply means transferring that cost into astronomical fuel bills, extra equipment, and considerable operational heartache.

• Genetically Modified Organisms (GMO): While genetically modified cereal varieties engineered for disease resistance and higher yields are widely cultivated in some parts of the world, their use in whisky remains sharply divided by geography and law. The Scotch Whisky Regulations strictly forbid GMO cereals, requiring non-GMO certification for every grain delivery. In other distilling regions, distilleries must decide whether the economic convenience of GMO grain is worth the risk of alienating consumers or closing off export markets where GMO ingredients are restricted.

The Certificate of Analysis (CoA)

Distilleries do not take the grain merchant’s word on trust. Every shipment of malt or raw cereal arrives accompanied by a Certificate of Analysis (CoA), a dense scientific document that lays out the exact physical and biochemical properties of the consignment.

By examining parameters such as moisture content, total nitrogen, grain size distribution, and predicted extract, the distillery can verify that the delivery meets its purchase specification before the grain is tipped into the silos. The table below outlines the core parameters typically found on a malt certificate of analysis:

As a raw material for spirits production, cereals must:

• Be free of fungus and moulds

• Be physically undamaged (no broken corns)

• Be uncontaminated with other cereals, weed seeds or any other debris

• Have the correct dry matter content (neither too much nor too little water)

• Contain an appropriate amount of starch.

Let us look more closely at the specific cereals used in the world of distilling, and their various characteristics.

Maize (Zea mays)

Maize (corn) is the largest crop in the world today. It is grown globally in warm and temperate climates and is used for human consumption, animal feed and in beverages.

Maize is part of the grass family (Poaceae) as shown in the taxonomy (Latin names assigned to the specific plant) below:

Family: Poaceae

Genus: Zea

Species: Zea mays

Maize is popular in distilling; it is easy to handle and has a sizeable starchy endosperm, below. The endosperm contains all the starchy cells. The embryo is the area of the grain that is alive; when you plant it, it grows roots and leaves. The starchy endosperm serves as food once the kernel is in the ground.

The starchy endosperm can be 71-80% of the dry weight percentage of the kernel, whereas the embryo can be between 10-15%.

Wheat

Wheat is the second largest crop globally. It thrives in warm and temperate conditions. This critical grain originated from the Euphrates valley, but is today cultivated on every continent.

Soft winter wheat is a good source of starch, and it can be between 65-70% of the kernel’s dry weight. It has a smaller embryo (germ) than maize, and the wheat embryo is around 3% of the dry weight of the total kernel.

The taxonomy below shows that wheat is also part of the grass family:

Family: Poaceae - Grass family

Genus: Triticum

Species: Triticum aestivum

The longitudinal section of the wheat kernel above shows all the components in the wheat kernel. You can see that the starchy endosperm is the most significant component.

Rye

Rye is a hardy plant that grows where other cereal crops will not. It thrives at high altitudes and can withstand very low temperatures. Modern rye production is mainly in Europe, Asia and North America.

The starchy endosperm makes up 86% of the total kernel weight (dry basis). Using rye in the distilling process imparts a distinctly spicy flavour to the spirit.

Family: Poaceae - Grass family

Genus: Secale

Species: Secale cereale

Figure: Longitudinal section of a rye kernel

Sorghum

Sorghum originates from South Egypt, where its cultivation started around 8000 years ago. Sorghum grows all over the world, in warm climates. It is a resilient crop as it can tolerate drought and extreme heat. This toughness makes it an ideal crop to plant in dry, arid areas where other crops, for example, maize, would quickly perish. Sorghum is a source of food, fuel and building material.

Sorghum is also part of the grass family.

Family - Poaceae (Grass)

Genus - Sorghum

Species - Sorghum bicolour

Species - Sorghum propinquum - sorghum

Sorghum is consumed as food and animal feed. It is also used to produce alcohol. Its popularity is increasing due to its adaptability in difficult climates where other crops will not survive. In 2016, the top 10 producers globally were the US, followed by Nigeria, Sudan, Mexico, Ethiopia, India, Argentina, China, Niger and Australia, the tenth largest producer.

The sorghum kernel does not have a husk. This results in the starchy endosperm, which makes up the majority of the kernel’s dry weight, around 86%. The embryo makes up 3.5% of the kernel’s dry weight.

Rice

Rice is the third largest commodity in the world and the most important cereal for human consumption. Although it originated in China, there are 40,000 different varieties of rice cultivated around the world. Rice has been a part of the human diet for at least 4,000 years; it is a rich source of sugars, protein and B group vitamins.

New varieties of rice can tolerate drought, floods and salty terrains. As rice is grown through submerging it in water, the most significant risk to the crop is through bacterial and fungal diseases.

Also part of the grass family, we can use rice raw to produce alcoholic beverages such as rice wine and sake.

Family: Poaceae - Grass family

Genus: Oryza L. - Rice

Species: Oryza sativa - Asian rice

Species: Oryza glaberrima - African rice

Rice is the most widely consumed staple food in the world, especially Asia. Rice cultivation is very labour intensive; it grows in areas with high rainfall. We can flood the area where rice is growing to reduce weed growth, as well as deter vermin. Rice can grow under irrigation, but it requires more effort to weed and control pests.

Figure: Longitudinal section of a rice kernel

In rice, the endosperm is 90-92% of the dry weight of the kernel, whereas the embryo is 3.3%. It has no husk, but it contains a seed coat that protects the kernel. The seed coat is known as bran. The figure above shows the longitudinal section of the rice kernel.

Barley

Wild barley originates from western Asia and northern parts of Africa. Barley cultivation started 8,000 years ago, and it is the fourth biggest cultivated crop today, behind wheat, rice and maize.

Barley is part of the grass family. The taxonomy of barley is as follows:

Family = Poaceae

Genus = Hordeum

Species = vulgare (six-row barley)

Species = distichon (two-row barley)

Barley’s starch and enzymes are very valuable to distillers. Barley either has or can manufacture α- and β-amylase. These enzymes are critical in breaking down starch to fermentable sugars. It has a similar or lower amount of starch on a dry weight basis (57-88%) to maize (71-80%) and wheat (65-70%), but it is still very beneficial for distilling as it malts easily.

As with brewing, we select varieties for their agricultural potential, e.g. their yield (tonnes per hectare), and disease resistance, etc. We also select them according to their malting potential, e.g. ease of malting, yield of malt, and extract potential. The Agriculture and Horticulture Development Board (the AHDB) approves barley varieties in the UK. The AHDB hosts a committee made up of interested parties, e.g. brewers, distillers and seed merchants. Similar boards exist elsewhere in the world for other regions.

What is a variety?

The word variety originated in the late 15th century. It comes from the Latin word varius or varietas , which translates into the word various in English.

A variety is a name given to a plant produced from parents in the same species. Barley can be either six-row or two-row. The barley grains form on the ear through fertile spikelets. There is a triad (group of three) spikelets at each node (refer to image below). Each of these has the potential to form a grain but only the middle spikelet in two-row barley will develop a kernel, whereas all three in six-row barley will develop a kernel.

By crossing two parents that are two-row barley, the resulting plant will also be two-row.

Sometimes, breeders choose to cross varieties. They will choose to cross breed them for typical characteristics such as those listed below:

• A better yield that gives more tonnage per hectare (t/ha)

• Shorter, more rigid straw

• Better disease resistance

• More uniform grain

• Better extracts potential (more starch and more fermentable sugars)

• Easier to process

Careful breeding between parents with the desired characteristics has led to the development of improved varieties. The breeding program is a long and labour-intensive process; it takes many years to get approval for a new variety. One trait bred out of the varieties is the precursor of ethyl carbamate. This compound, discovered in beverages like whisky, is a known animal carcinogen (can cause cancer). The precursor for this dangerous substance was found to develop during the malting process of barley. We will expand upon this .

An alternative way to breed involves genetically modifying the barley to produce the ideal characteristics.

We have now finished describing the cereals most commonly used in distilling. We will now explore the ‘honorary cereals’: sugar cane and sugar beets. Sugar cane is part of the grass family (Poaceae). You will notice that sugar beets belong to a completely different family (Amaranthaceae). These two commodities also differ from the cereals we were discussing in the previous sections, as they contain sugar, not starch.

Key Takeaways

Barley remains the aristocrat of distilling grains because it generates its own starch-converting enzymes during malting. Unmalted cereals like maize and wheat offer cheaper, higher starch yields for grain whisky, but require external cooking and enzymatic help to release their potential.

About the author

John Fegan · Editor

John has run Uisge Beatha since 2015 and Whiskipedia.com since 2020. He owns whisky casks and writes from direct experience of their storage, insurance and bottling decisions.

• johnfegan.org