Understanding Whisky Production · Unit 3: Raw Materials Processing

Chapter 6: Milling and Mashing: Grist Proportions and Starch Conversion

Roller mills, plansifters, the classic 70/20/10 grist ratio, and how alpha- and beta-amylase convert starch into fermentable sugars.

Once malt arrives at the distillery, it must be crushed into grist. This sounds straightforward until one considers that grinding it too fine creates an impermeable paste resembling library wallpaper paste, while leaving it too coarse means hot water cannot reach the starch inside.

The time-tested compromise is the classic ratio: roughly seventy percent grits, twenty percent husks, and ten percent fine flour. The husks form a porous, natural filter bed at the bottom of the mash tun, allowing warm water to percolate through. At precisely 63°C to 65°C, two key enzymes awaken: alpha-amylase chops long starch coils into manageable segments, and beta-amylase snips off sweet pairs of glucose molecules to create fermentable maltose.

Grain Intake and Storage

During delivery, the CoA (certificate of analysis) and visual checks will determine whether the grain is to be offloaded or rejected (Step 1 in the high-level flow diagram below).

You need to check for the following before accepting the batch:

• Verify the batch details against your delivery plan.

• Do a visual assessment of your grain. What do you need to look for when you visually assess the malt?

• It must be free from pests.

• Grain should not contain any live pests, such as weevils, beetles, moths, birds or rodents. If we notice insect damage on the kernels, it is critical to analyse the batch for live insects. Weevils can often be present within the kernel and are not always visible at first glance.

• The kernels must be uniform in size.

• Kernel size should not vary excessively in size, as it will affect milling efficiency.

• Verify that damage to the kernels falls within acceptable levels.

• The grain will have some degree of damage, e.g. broken kernels. It is crucial to inspect the grain before offloading. Every time you move the kernels, it damages the starchy endosperm, reducing the future extract potential.

• Inspect and check that the grain is free from foreign material.

• Foreign material is anything that is not the grain. The CoA will indicate the acceptable level of foreign seeds or other materials, depending on the legislation. There are strict rules regarding poisonous seeds and rejection of batches.

• Grain should not have any indication of mould growth.

• Mould growth should not be present. When it is present, it indicates either that the moisture was high at the dispatch of the grain batch, or that there was moisture ingress during transit.

• Grain should not have any strange smells when you open a bag or truck.

• When you smell the grain upon opening the rail carriage, truck or the bag, it should smell fresh, and like grain. There should not be damp or other strange aromas present. Microbial growth can give the malt a damp smell, like a cellar, or even a sour smell. Drying grain incorrectly with diesel-powered dryers can contaminate the grain with a diesel aroma.

Once you are happy with the quality of your grain, you are now ready for the intake (Step 2 in the high-level flow diagram). You must always keep health and safety requirements and considerations in mind. Large plants that offload into silos, will have grain elevators, magnets, combi-cleaners (classifying screens with an additional dust extraction section) and dust extraction. Smaller plants must have dust extraction and magnets, as a minimum, to reduce the risks of human exposure to dust and dust explosions. Operator interaction with dust can lead to pulmonary uvulitis, conjunctivitis or other ailments. Long term exposure to dust should be managed by decreasing exposure and using personal protective equipment (PPE) such as filter face masks if interaction is a requirement.

The general rule is that where any grain is moving and producing dust, dust extraction must be in place. The risk of a dust explosion is always present. One way to minimise the risk is to use good housekeeping, e.g. keeping the area free of dust, pests and ignition sources.

Removing foreign material from the grain during intake into the storage units is good practice. We can also remove it just before the grains go through milling. Equipment such as de-stoners remove stones (possible ignition sources), which are a similar size to the grain. Combi-cleaners are common in distilleries for removing coarse (e.g. broken kernels), fine (dust), stones (usually larger than the grain), and low-density material (loose husks). Magnets, either permanent or electromagnets, are vital for removing metal particles during intake. They are also used before the mill to remove possible ignition sources. Another way to reduce the risk is to electrically ground all the equipment.

If you remove just one factor, the dust explosion cannot occur.

Grain Storage

Until you are ready to use the grain you must ensure it is stored safely. Stocks of grain at a distillery will be kept to a minimum level to save costs and manage the businesses cash flow. Grain that is stored must be kept dry and free from infestation of any kind e.g. rodents and insects until it is ready to be used. Grain is often stored in silos and these must be free from leaks, clean and ideally self-emptying. Grain can also be stored in bags. These bags must also be kept in conditions that are dry and free from infestation.

Calculation of Grain Quantity Required

One of the most important things for a distiller to know is how much grain they will need in order to produce a given quantity of wort, at the desired strength. Wort collection is discussed in more detail later and in further lessons but you need to understand how it’s measured because it is an input for this calculation.

Distillers and brewers measure wort strength in a variety of ways. Here, we will refer to the Specific Gravity (S.G.) measurement a standard measurement in distilling. Specific gravity is a way of showing the density of a substance in relation to a reference substance, typically water. Confused? That’s ok. Let us break things down a bit.

We know that density is defined as a substance’s mass divided by its volume. Essentially, density tells us how much mass of a substance fills a specific amount of volume. We also know that water has a density of 1.000 g/mL at 4˚C., which means that one mL of water weighs one gram. Something denser than water would have a higher weight per one mL. Specific gravity is simply showing the ratio of that substance in relation to water. So back to our wort.

If our wort has a density of 1.060 g/mL, and water has a density of 1.000 g/mL, we then know that the specific gravity of our wort is equal to 1.060 g/mL divided by 1.000 g/mL, which is simply 1.060. Notice that the units cancel out in the equation, so specific gravity is a unitless quantity. (The actual definition of specific gravity is much more complicated than this. However, as distillers, we do not often need to worry about that.)

Brewers and distillers often multiply specific gravity by 1,000 and then subtract 1,000. Unbelievably, this actually makes talking about gravity far simpler. For example, if our specific gravity were 1.060, we would multiply that by 1,000, which gives us 1,060. Subtract 1,000 from 1,060, and we are left with 60. This is often referred to as excess gravity, and 1,060 would mean that there are 60 points of excess gravity. See? Not that hard.

OK. Back to calculating our grist weight. In order to calculate the amount of grain needed for a batch of whisky, we need to know three things:

1. The desired excess gravity of the wort we are trying to create
2. The volume of wort that we need
3. The amount of soluble extract that our grain contains

As distillers, we decide the wort gravity, so there is no problem here. We also decide the volume of the wort. The only thing we have to look up is the soluble extract value for our grain, which if you remember from the raw materials lesson on cereal, is not too hard to find.

The equation for our grist weight looks like this:

This is a simple plug-in calculation. Do not worry about 3.87 - it is a simple factor to make sure that everything comes out correctly. So, let us try this equation with our 1.060 specific gravity wort. We will assume that we want 10,000 litres of volume, and that our barley has a soluble extract of 77.5%.

Pretty simple, yes?

Milling Process Overview

The purpose of milling is to expose the starch. Milling breaks away the husk from the starchy endosperm, whilst also reducing the particle size of the starchy endosperm.

Milling increases the surface area of the starch granules available, which assists in the conversion processes that take place during mashing. Various mill types are available today; we will now investigate the most common designs and consider how they manage to separate the husk from the starchy endosperm.

Milling Technology - Two-roller Mill

The most basic mill is the two-roller mill. It is also known as a grist or agricultural feed mill. The name gives you a clue about its operation. It uses two rollers to crush the grain. The operation of a two-roller mill is the basis of the design for other dry mills with multiple rollers. The figure above shows that the rollers turn in opposite directions, allowing the flutes (grooves) on the rollers to grip the kernels. The area between the rollers crushing the grain is known as the mill gap. It is important that we align the feed of the grain with the middle of the rollers, to ensure that the rollers grip and crush the grain. Mill gap optimisation is important in order to produce correctly sized particles. The crushed grain (grist) coming out of the mill rollers consists of flour, grits and husk.

Grist - A term used for milled grains that are ready for use in mashing. Grits - A term used to describe a crushed grain endosperm particle after milling.

The grist composition will differ depending on the type of mill you use. Two-roller mills do not give you any real flexibility, other than changing the mill gap setting to control grits size distribution. By flexibility we mean the types of grains that can easily be crushed. Some unmalted grains such as wheat and rye benefit from having several sets of rollers that have progressively tighter gaps between them. This allows for much better particle size control. Let’s take a moment to look at these types of mills in more detail.

Those distilleries that use two-roller mills do so due to the higher capital cost of four- or six-roller mills.

Milling Technology - Four-roller and Six-roller Mills

In addition to the two-roller mill, there are two other commonly used roller mills; the four-roller and six-roller.

Four-roller Mills

The figure below shows a typical four-roller mill. The first rollers will detach the husk from the endosperm. The husk and flour are separated, sending the coarse grits through another set of rollers to reduce their size. A four-roller mill is suitable for well-modified malts, since the starchy endosperm is accessible with no residual β-glucan cell walls after the completion of malting. The distiller easily controls the particle size, and the grist composition is made up of grits, flour and husk.

Six-roller mills

Milling less modified malt typically requires a six-roller mill. The function of a six-roller mill is similar to that of a four-roller mill. It just has an additional pair of rollers and sieves to give even more control over particle size.

Milling Technology - Hammer Mills

Roller mills are not suitable for distilleries using green malt and other unmalted or undermodified grains. Enter the hammer mill.

The figure of the hammer mill above shows the free-swinging metal hammers attached to a rotor. The hammers crush the grain into smaller pieces, and the sieve separates the required smaller-sized particles from the larger pieces. The hammer mill operation is similar to that of the friabilimeter, which measures how well and how easily the malt crushes. However, in the friabilimeter, the grain is crushed against the sieve, whereas in the hammer mill, the hammers crush the grain.

Grist Analysis

It is essential to analyse the grist after milling, to ensure that both the composition percentages and the actual size of the crushed starchy endosperm (grist), are acceptable (husk, coarse grits, fine grits, flour). We must visually inspect the grist as frequently as possible, especially if there is a raw material change, such as a new batch.

Grading sieves (plansifter) give an accurate analysis of the different fractions of the grist particle size distribution. Sieves with various sized holes separate the different particles in the grist. Depending on the method, the number of sieves can vary. However, the EBC (European Brewery Convention; the technical group in Europe that among other things decides the testing parameters and standards for brewing ingredients, and by default distilling ingredients) method typically has five sieves, with a pan at the bottom for flour, and a lid. You can manually shake the sieve; however, you will obtain results that are more accurate by using an automated shaker with a timer. Using this method would provide the grist with the same motion and time duration, and achieve the same results.

Visually, a sample should have big pieces of husk, small pieces of crushed endosperm, and some flour. The table below shows typical results for grist analysis using the EBC method. Roller mills preserve more husk than a hammer mill. A roller mill produces larger particle sizes than you would get from the same fraction taken from a hammer mill.

The figure below shows the visual distribution of the particle sizes. We will compare how these fractions influence the type of vessels that you will use during the process.

Figure: Visual illustration of EBC plansifter grist fractions

Effective distilling operations require regular assessment of the grist composition.

Before we learn how the grist composition affects the process, we need to look at the high-level wort production process used in distilling.

After milling, the next step in the process is mixing the grist with water, known as mashing (as shown above). Milling directly affects the efficiency of mashing and the amount of sugars produced.

The liquid produced during mashing is known as wort. All the solid material that could not dissolve in the water is known as draff.

Mashing Process and Technology

The mashing process will differ depending on the raw material used. In this section, we will explore how to mash with malted grains, or grains with similar characteristics to malted barley. We will also identify the necessary technology required.

The purpose of mashing is to extract (dissolve) all the starch from the malt and convert the starch to fermentable sugars.

At this point in the process we have milled the grains to expose the starchy endosperm. Next, this grist needs to go into a mashing vessel. This vessel requires water to allow the starch to go into suspension. A basic mashing system contains the following components that enable this:

• A mill or a system that can deliver the grits to the mash tun - you can transfer the relevant grain, such as malted barley, into a grist hopper before milling. Alternatively, you can manually add the pre-milled grist.
• Temperature controlled water supply
• Mashing vessel that contains: Optional rakes, blades or a paddle for stirring the mash A slotted (perforated) base to hold back the solids therefore separating the wort from the spent grain (residual solids)

The first step in the mashing process involves mixing the milled grain with the temperature-controlled water. The amount of water added will determine the mash consistency, also known as the liquor to grist ratio. A high liquor to grist ratio indicates that a large amount of water is part of the mash, producing a thinner mash compared to a low liquor to grist ratio. Ideal figures for water mixed with grist are between 2.5-3.5 L of water per kg of dry grist. The liquor to grist ratio is also important when it comes to preserving malt enzymes. High heat can denature enzymes making them lose their activity and subsequently causing a thicker mash. A lower liquor to grist ratio will heat up more evenly, and better protects the enzymes.

It is vital to effectively mix the grain and water. Manual mixing, or the use of screws or static mixers (Steeles Masher or grist hydrator) in automated plants, ensures that each of the starchy endosperm grits is in contact with the water. Hydration is vital in order to prepare the starch granules for the conversion process. The dry grits of starch are not yet fully accessible for breakdown by α- and β-amylase (enzymes that you learned about in the malting process lesson). What is the process that starch needs to undergo, in order to be ready for conversion? We will find out in the next section.

Mash Conversion Biochemistry

During mash conversion, the starch transforms to promote the production of sugars. This transformation is known as gelatinisation. Once gelatinisation occurs, the next steps of starch conversion can happen; liquefaction and saccharification.

We know that starch consists of long glucose chains.

The bonds between the glucose molecules are not all the same, and this leads to differences in the structure of the long chain. The two important types of starch chains are amylose, which makes up 25%, and amylopectin, which makes up 75% of the starch granules.

Let us take a couple of steps back and start at the beginning of the biochemical process.

After milling, the crushed starchy endosperm contains starch granules and residual protein matrix. The starch granules themselves are roundish structures, with alternate layers of amylose and amylopectin. The granules differ in size, with a ratio by number of 10:90 large to small granules. The large granules are known as Type A, and the small granules as Type B. The figure below shows the different types of starch granules. The granules appear compact and require more steps in order to enable conversion to fermentable sugars.

Both amylose and amylopectin are present in starch granules, but they have a closed and compact structure, such as that shown in the first image in the figure above. This configuration does not support conversion of starch to sugars, since large parts of the chains are not in contact with the water. Only α-amylase can convert the starch granules, but at a very slow rate - much too slow for distilling. To open up the structure, we must firstly achieve a specific temperature, known as the gelatinisation temperature. This is determined by the grain variety and malting conditions. The table below shows the typical gelatinisation temperatures for different grains.

The shapes of the starch granules also differ between the grains. The scanning electron microscope images below show the differences in wheat, barley and rice granule shape. Wheat and barley have similarly round granules, whereas rice granules have a polygonal shape.

Once the gelatinisation temperature has been reached, the process known as gelatinisation will occur.

Gelatinisation - This is a vital stage in mashing. The term refers to the process by which the tightly bound starch molecules unwind due to the action of heat and water. Gelatinisation allows them to dissolve. Enzymatic activity then breaks them down.

The figure below shows the amylose and amylopectin chains, now free to be broken down by α- and β-amylase.

Once the starch structure unwinds, water can enter deeper into the starch polymers. This process is known as liquefaction. Water acts as the medium that will facilitate all the critical enzymatic reactions during conversion.

Achieving the gelatinisation temperature of the grain’s starch granules allows for complete hydration (liquefaction), and then the conversion of starch to sugars.

Saccharification is the process in which enzymes break starch down to sugars. It occurs after the complete hydration of the starch granules, which exposes the amylose and amylopectin chains.

Saccharification is the biological hydrolysis of biomolecules such as starch. Hydrolysis - from the Ancient Greek word hydro . Hydro means water. Lysis means ’to unbind’. The saccharification process in mashing uses the various enzymes to unbind the sugar molecules from the amylose and amylopectin chains.

The diastatic enzymes (starch degrading enzymes), α- and β-amylase are critical for the conversion process, but they will not be useful if the starch granules have not gone through the gelatinisation process, or if they have experienced suboptimal processing conditions. All enzymes have optimal ranges in which they perform best. Parameters such as temperature, time and pH, however, will influence the performance of the different enzymes.

Mash Conversion Enzymes

PH, temperature and time all affect the activity of enzymes such as barley α- and β-amylase.

The ideal pH range for α-amylase action is 5.6-5.8, with a corresponding temperature range of around 70˚C-75˚C. β-Amylase activity is optimal within a pH range of 5.4-5.5, with a temperature range from 63˚C to 65˚C. Enzyme activity decreases outside these ranges. This is why it is important to find the best temperature between 62-65˚C, and the ideal pH for mashing to ensure that both α- and β-amylase are optimally breaking down the starch chains. There is an optimal time for the enzymes within their stated ranges, which will ensure complete conversion. After this optimal time, typically 30 min, the wort concentration plateaus, but the sugars in the wort will be broken down to more fermentable sugars.

We need to look at the specific actions of the two enzymes, in order to understand how they will affect the wort. The figure below shows where α- and β-amylase will attack the starch chain, be it amylose or amylopectin. The figure represents a fragment of amylopectin, showing the branched section:

Did you know? The products from the diastatic enzymes are: Glucose - One glucose molecule. Maltose - Two glucose molecules in a chain. Maltotriose - Three glucose molecules in a chain. Dextrin - These are carbohydrates that have not been completely converted to fermentable sugars by amylases often due the presence of α-(1,6) branch points.

Malted barley contains two additional enzymes that break down starch. They are limit dextrinase and α-glucosidase (maltase).

Maltase has a low level of activity, but with enough time, it can break down the starch into glucose (as shown in the figure above).

Limit dextrinase will break the starch chain at the branching point, producing two new linear starch chains that can be broken down to fermentable sugars.

Limit dextrinase:

• Provides additional extract and fermentability through using limit dextrins; the small starch residues left after mashing typically containing eight glucose units. This process is also known as secondary conversion.
• Is not active at mash pH but becomes active in the washback as the pH drops to e.g. 4.5.
• It therefore needs to survive the mashing stage. This requirement can be difficult because it is heat sensitive.

All enzymes are heat sensitive and are mostly inactivated towards the end of mashing. All the above-mentioned enzymes play a role in converting starch to fermentable sugars during the mash conversion process.

In brewing, the starch is converted in the mash tun before wort collection is started. The mashing-in temperature is typically 62-65˚C, rising to 70-75˚C before run-off. This reduces viscosity, but limit dextrinase will not have worked, and will have been denatured. The limit dextrins will not be broken down and in fact are important to give “body” to beer. This is not a key consideration for distillers.

In distilling, run-off (wort collection) commences as soon as possible, usually after a short recirculation (note, not all distilleries want a clear wort). The mashing temperature of 62-65˚C ensures that limit dextrinase survives into the washback. Dextrin breakdown ensures maximum extraction of sugars, and hence higher Lpa/t.

Various factors that will influence enzyme efficiency include: • Temperature We have learned that each enzyme has an optimal temperature range. Any temperature outside of this range will reduce the enzyme’s effectiveness. • pH Similar to temperature, pH values outside of the optimal range will negatively affect the enzyme’s performance. • Liquor to grist ratio Thicker mash that has a lower water to grist ratio will protect the heat-sensitive enzymes better than a thin mash. • Time Additional time will not give you more extract, but it can give you more fermentable sugars. This, however, is only true if the temperature is adjusted to match the required enzymes’ optimal conditions.

The mash conversion process described thus far, applies to typical grains such as barley, wheat, oats or rye, which all gelatinise at mashing temperatures below 65˚C. They can be milled and mashed without additional steps. However, what if you decide to use maize, rice or sorghum? The gelatinisation temperatures for these grains are between 70-80˚C. The maize, rice and sorghum do not yet contain α-amylase because they do not go through a malting process. Maize β-amylase has an optimal temperature of 50-55˚C; its activity decreases with increasing temperature. The process to gelatinise the starch, for example in maize, will denature the β-amylase. α-Amylase is not yet present to convert the starch. Using these grains with high gelatinisation temperatures requires a separate processing step, called grain cooking. It also requires an external source of enzymes (e.g. malted barley for Scotch grain whisky) to convert the starch. We will now examine the finer details of grain cooking.

Grain Cooking Process and Technology

The purpose of grain cooking is to gelatinise the starch of grains that did not go through a malting process.

We have already mentioned that efficient starch conversion requires starch to gelatinise first. The long starch chains must absorb water, and open to allow the enzymes to attack. A separate vessel is necessary for the cooking process. The figure below shows a typical grain cooker. The key components of this vessel are:

• Inlet and outlet for the grain
• Heating surface
• Agitator - to keep the grain in suspension and ensure even cooking

Cookers can have different capacities, varying widely from 2-40 t. The cooker commonly uses steam to heat the mash. At the start of the process, the steam flushes out the air before closing the vents; steam injection continues until the desired pressure is achieved. We should use only food grade chemicals with no carry over to produce the steam for direct injection. No impurities or substances that could cause harm to the consumer should be present.

Three factors can determine the effectiveness of the cooking process:

1. The pressure reached, which will result in the correct temperature, typically 140˚C and 4 bar g steam.
2. The duration spent at the correct pressure, typically about an hour.
3. Water/grist ratio

The flow diagram below shows the cooking process for most grain cookers.

Variations on this typical process can include milling the grains to flour and using water from the process to reduce water usage.

Backset is the thin watery liquid that remains after distillation; it also includes unfermented solids.

Backset is acidic; adding it to the grain cooker with the mash promotes the breakdown of the grains in the cooker. The acidity of the backset helps to adjust the mash pH to an optimal pH range of 5.4-5.6.

The typical cooking process, s above, is a batch process. Batch cooking at atmospheric pressure is widely used in the production of whisky. Whereas grain neutral spirits use both batch and continuous cooking under pressure. Continuous cooking under pressure is a process where the mash is pumped through a cooker, exposing the mash to temperatures of 170-177˚C and 7 - 9 barg for two to six minutes. Cooling of the cooked mash to 63˚C occurs in a flash chamber, before mixing with a continuous stream of malt slurry. The mixture of cooked mash and malt slurry cools to fermentation temperatures (typically 20˚C) through a water-cooling system, before it enters the fermentation vessels. The continuous cooking process is more complicated; any delays during the process will waste energy or overcook the mash. The process needs to maintain a steady state in order to ensure efficiency.

Common factors to consider when using a continuous system include the following:

• We need to use fine ground grain, typically hammer-milled grain.
• We need to add a small quantity of malted barley to reduce the slurry’s viscosity. This is also known as pre-malt or malt slicker. In GNS (grain neutral spirits) production, this requires an exogenous α-amylase.
• Pumping of the grain slurry occurs through a relatively narrow tube.
• There is a control of residence time.
• Cooking uses high pressure and temperature. It can be higher in continuous cooking than what would be possible with batch cooking.

Both the batch and continuous cooking processes require a mash temperature of around 64˚C, which if you recall, is the optimal conversion temperature for barley malt α- and β-amylase. The distiller can now choose to add barley malt as a source of enzymes or exogenous enzymes, if permitted by local legislation. Exogenous enzymes are not permitted for Scotch whisky. If permitted, exogenous enzymes are a good substitution for malted barley, and perform better at higher temperatures. They are enzymes obtained from a different source, for example from fungi or bacteria.

Exogenous Enzymes

As we learned in the preceding section, working with unmalted cereals can present challenges. The primary issues are the gelatinisation and conversion of starch in mashes with low enzyme content. The previous section dealt with gelatinisation and conversion when malted barley is available. However, what happens at those times when there is no malt to add for conversion?

Some producers of grain neutral spirit are disinterested in using malted barley in any capacity, due to its added expense. In this case, exogenous enzymes will be used to break the starch molecules down into fermentable sugars. Let us look at the major enzymes used in the distilling industry.

The goal of starch conversion is to produce a fermentable wort, containing the nutrients that our yeast needs to convert sugar to alcohol. We can accomplish this in systems without barley malt enzymes by adding exogenous enzymes.

Exogenous enzymes are any enzymes that the distiller adds, i.e. they are not from the grains used in the mashing process. These enzymes are usually produced by bacteria or fungi, and then isolated and packaged in sanitised containers. Since these enzymes come from different sources, they behave slightly differently to the enzymes for barley malt. The effect they have on our grain starch is the same, but they will often be able to work at higher temperatures (some as high as 90˚C or more) and within wider pH ranges.

Four main enzyme types are frequently used in the distilling industry. There are a handful of others, which are beyond the scope of this guide (due to the rarity of their use). The four main types are as follows:

1. Α-Amylases
2. Amyloglucosidases
3. Proteases
4. Pullulanases

Amylases and amyloglucosidases are by far the most common enzymes used, so let us talk about these first.

Commercial α-amylase preparations work very similarly to their barley malt counterparts. Their primary function is liquefaction and to begin breaking down the larger starch polymers. Much like barley amylase, they tend to randomly clip starch polymers apart, reducing them in length and size. While this does produce a few fermentable sugars along the way, used by itself, this group of exogenous enzymes will not produce the most fermentable of worts in an unmalted cereal mash.

This is where the use of amyloglucosidase comes in. Sometimes referred to as glucoamylase, this enzyme does an excellent job of converting starch to fermentable sugars. It quickly breaks apart α-(1,4) bonds, forming many glucose molecules in the process. Amyloglucosidase also breaks α-(1,6) bonds, meaning that it can debranch amylopectin polymers. However, it does this at quite a slow rate.

Let us now discuss proteases. Used only occasionally, these enzymes catalyse reactions involving proteins. In this case, they break down proteins, specifically the protein matrix surrounding starch molecules. Remember that during the malting process, this is done for us by barley-derived proteases. However, we are talking about grains that have not undergone any malting. Therefore, they may still have a lot of protein surrounding the starch granules. This protein needs to be degraded before the starch granules can be gelatinised and undergo liquefaction. Proteases are perhaps most commonly used on unmalted wheat.

The final exogenous enzymes that we will discuss are the pullulanases. These enzymes are called debranching enzymes because they specifically target α-(1,6) branch points in amylopectin. They are most commonly used in conjunction with other enzymes such as an amylase and amyloglucosidase preparation. While amyloglucosidase can also serve as a debranching enzyme, the pullulanases are usually much faster.

Key Takeaways

Mashing is a strict thermal balancing act. Strike water temperatures must be controlled within narrow margins: hot enough to gelatinise barley starch and activate amylase enzymes, but cool enough to avoid denaturing them before conversion is complete.

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