Unit 5 - Milling Flashcards
What are the two primary forces used by a roller mill to break down grain?
Compression and shear
Compression deforms the grain until it fractures, while shear tears the grain apart.
What is the function of a feed roller in a roller mill?
To distribute and orientate the grain correctly for milling
It ensures a consistent flow into the main rollers.
Why is it important for grains to enter the rollers tip first?
So they can be split longitudinally
This is a more efficient way to break them down.
How does the diameter of a roller affect the nip zone and the rate of grain throughput?
A low roller diameter results in a smaller nip zone and a lower rate of throughput
Smaller diameter rollers provide a smaller crushing area, leading to less complete crushing.
What are three factors that determine the throughput of a pair of rollers in a mill?
- Speed of rotation
- Size of the mill gap
- Length of the rollers
In multi-roller mills, throughput is limited by the slowest set of rollers.
What is fluting in roller mill design?
Grooves milled into the roller surface
Its primary purposes are to increase the coefficient of friction and enhance shearing action.
How does the density of flutes typically vary?
Typical fluted rollers have 6.5-10 flutes per cm of circumference
This density is designed for optimal grain handling.
How does the twisting of flutes on a roller contribute to the milling process?
It increases the shearing action on the grain
This action is compared to wringing out washing.
What are the two main edges of a flute?
- Cutting edge
- Rear edge
The arrangement of these edges on opposing rollers affects the milling action.
What flute edge arrangement is typically used for rollers processing husk?
Rear edge against rear edge arrangement
This arrangement emphasizes crushing.
What arrangement is common for producing grits?
Cutting edge against cutting edge arrangement
This is used to achieve a finer particle size.
Why is the specification of grain size and the screening of malt important for roller mills?
Mill rollers are designed to work with a specific size of feed material
Introducing different sized grains can lead to inefficient milling.
What is the typical diameter of modern mill rollers?
Around 250 mm
This size is ideal for working with typical grain sizes.
Is increasing the speed of the rollers always beneficial for throughput in a roller mill?
No, increasing speed may reduce throughput if the mill is already operating optimally due to grains bouncing around, which is called ‘riding the rollers’.
What does compression of the grain in a roller mill primarily cause?
Compression causes the grain to fracture, reducing particle size but does not strip the husk away from the endosperm.
True or False: Husk integrity is more important in a grist for a mash tun than for a lauter tun.
False. Husk integrity is equally important for both vessels.
What primarily determines the particle size produced by a hammer mill?
The holes in the screens are most significant in determining particle sizes, not the rotor speed.
What is extract efficiency?
Extract efficiency is the amount of extract in the wort as a percentage of the amount of extract in the grain.
Fill in the blank: A narrower mill gap produces ______.
[finer grist]
What should be checked before adjusting the mill gap to improve extract efficiency?
Wort separation and plansifter analysis of the current grist.
After adjusting the mill gap, what should be checked to ensure proper settings?
Use a feeler gauge to check the new gap and run some card through the rollers to ensure they are parallel.
What is shear in the context of roller milling?
Shear is when an object is subject to forces from opposite sides, aiding in the comminution of grains.
How is shear achieved in roller milling?
Shear is achieved through roller fluting and differential roller speeds.
What does malt modification refer to?
Malt modification is the sum of the changes that occur during germination in the malting process.
True or False: Well-modified malt requires more intensive milling than under-modified malt.
False. Well-modified malt is easier to mill and requires simpler equipment.
What is a potential issue with over-modified malt?
It is brittle and difficult to mill without producing flour and dust.
What is the best mill for a mash tun using well-modified malt?
A four-roller mill.
What is the best mill for under-modified malt in a mash filter?
A hammer mill.
What are the hazards associated with malt dust?
Dust can cause respiratory issues, asthma, and even explosions.
What type of equipment is necessary in dusty environments to prevent explosions?
Non-sparking or intrinsically safe electrical equipment.
What does the hand examination of malted barley assess?
Homogeneity, varietal purity, damage, modification, infestation, moisture, foreign material, and colour.
What is the significance of checking for homogeneity in malted barley?
It ensures even kernel size, shape, and plumpness, which affects milling and extract potential.
How can pest infestations in malt storage be prevented?
By ensuring storage silos are pest proof, monitoring pest activity, and controlling temperature and moisture levels.
Fill in the blank: The ideal moisture level for stored malt should be around ______.
[4% moisture]
What can cause catastrophic damage during milling if not removed?
Foreign material.
What moisture level should malt be maintained at?
Around 4% moisture
What temperature minimizes pest activity in stored grain?
Below 15°C
What should be avoided in grain storage unless cooling with dry air?
Changes in temperature
What is a common practice for grain upon arrival to prevent infestation?
Fumigation
What is the consequence of significant pest infestation in grain?
The grain must be cleaned and disposed of
What is one advantage and one disadvantage of screw conveyors?
Advantage: Low installation costs
Disadvantage: High maintenance costs
What is one advantage and one disadvantage of pneumatic conveyors?
Advantage: Good for space-limited installations
Disadvantage: Can damage grain due to high velocities
What is a key design feature for safe grain storage in silos?
Silos must be sealed from the elements
What is the recommended angle of the cone for mass flow in silos?
Around 60°
What method can be used to estimate the volume of grain in a silo?
Using a plumb line to measure the distance from the top of the silo to the surface of the grain
What is the bulk density of malted barley?
Around 0.5 t/m³
What is a more accurate method for measuring silo contents?
Using load cells to measure the mass
What are the advantages of a six-roller conditioned dry mill?
Processes poorly modified malts effectively, yields greater extract efficiency
What is the primary function of the first pair of rollers in a six-roller mill?
Break up the kernel
Which mill type is best suited for producing a desirable grist from under-modified malt?
Hammer mill
What is a significant disadvantage of steep conditioned mills?
Cannot use plansifter for grist analysis
What design feature helps prevent over-comminution in a six-roller mill?
Screens between the rollers
What is a key characteristic of steep conditioned wet mills?
Preserve the husk for better wort separation
How does a steep conditioned mill mitigate hygiene issues compared to a full steep wet mill?
Less damp material and shorter residence time
What is the main advantage of using water in steep conditioned mills?
Helps control grist oxidation and reduces explosion risk
What is a key operational issue with full steep wet mills?
Difficult to operate consistently
What mill would be suitable for a small pub brewery using an isothermal mash tun?
A dry mill
What is the main reason to select a steep conditioned mill for medium-sized breweries?
Less husk damage and better wort separation
What is the production capacity of a medium-sized brewery specializing in export beer?
150,000 hL per year
What type of mash tun do small pub breweries typically use?
Isothermal mash tun
What is the main advantage of using isothermal mash tuns?
Both mashing and wort separation are undertaken in the same vessel
What milling option is best for achieving a particle size large enough to remain buoyant in a mash?
Two- or four-roller dry mill
True or False: Wet mills are suitable for areas of water scarcity.
False
What type of mills are best for lauter tuns?
Wet mills or six-roller dry mills
What is the importance of purging with CO2 or nitrogen during grist storage?
Minimizes oxidation of the grist
What types of mills are suitable for mash filters?
- Hammer mills
- Underwater disc mills
- DISPAX-REACTOR®
What is a key factor in preventing oxidation of lipids in malt?
Control of oxygen during the milling process
Fill in the blank: Effective intake checks will confirm that the grain meets the brewery’s _______.
[specification]
What can happen if storage conditions for malt are not maintained?
- Pests can damage grain
- Grain may pick up moisture or dry out
What is the role of dust aspiration systems in malt handling?
Keeps dust levels low and prevents explosions
What are the objectives of malt intake and storage?
- Produce required particle size distribution
- Maintain husk integrity
- Maximize extract efficiency
- Operate safely
- Achieve programmed brewhouse cycle time
What is a safety hazard associated with malt handling?
Dust generation
What must be ensured to maintain the required level of husk integrity?
Malt must be undamaged and at the correct moisture level
What is the recommended milling option for a brewery using a mash filter?
Hammer mill
What is the benefit of a six-roller mill over a two- or four-roller mill?
Better extract efficiency
What type of mill is recommended for a brewery with a lauter tun?
Six-roller mill
What should be done to prevent malt from becoming damaged during handling?
Gentle handling and regular checks
What is one aspect of milling that can affect flavor stability?
Damage to the acrospire
What is the primary function of an intake pit or hopper in a malt handling system?
Prevents ingress of pests, water, oil, and fuel
What is a requirement for bucket elevators in malt handling?
Must move malt vertically without damaging it
What is a requirement for the dust aspiration system in malt handling?
Maintains negative pressure in the system
What must be done to ensure safe operation of magnets in malt handling?
Regular cleaning to prevent overload
What is the significance of moisture level in the malt intake process?
Affects extract efficiency and grain damage
What is the recommended action for a system to prevent grist oxidation?
Flush with CO2 or nitrogen
True or False: Hammer mills can mill any type of grain.
False
What type of mill has lower energy costs, six-roller or hammer mill?
Six-roller mill
What is the main concern with using wet mills in water-scarce areas?
They use more water and produce more effluent
What is the primary function of the aspiration system in malt handling?
To collect dust from the malt handling equipment and prevent it from escaping into the workplace.
What are the key maintenance requirements for the aspiration system?
Regular checks for accumulations of dust, maintenance, and ensuring it is earthed to prevent sparks.
What safety measures should be implemented for silos?
Aspirated to minimize dust, access restricted, earthed to prevent sparks, and regular checks for explosive atmospheres.
List the requirements for silos.
- Store grain without causing deterioration
- Allow for ventilation and cooling
- Prevent water and pest ingress
- Allow grain sampling
- Enable safe and effective fumigation
- Allow grain to empty through mass flow
- Accommodate the angle of repose
- Determine contents of silo
What is the primary function of a destoner?
Removes foreign material with a density greater than that of malt.
What are the maintenance requirements for a destoner?
Regular maintenance, dust aspiration, explosion relief, and earthed to prevent sparks.
What are the requirements for malt screening?
- Removes foreign material outside malt size specifications
- Self-cleaning or easy to clean manually
- Collects foreign material for safe disposal
What is the primary function of malt weighers?
Accurately weigh the malt while causing minimal damage.
What are the key requirements for manual dust cleaning systems?
- Easily accessible
- Remove dust effectively
- Easy to keep tidy
What is the purpose of conditioning in malt processing?
To increase the level of husk moisture for better pliability and reduce fracturing during milling.
What is a critical factor to consider during milling?
Particle size distribution and degree of husk integrity suitable for wort separation equipment.
What is mashing in?
The filling of the mashing vessel with hydrated grist.
What are the goals of mashing in?
- Achieve correct water to grist ratio
- Set the required starting temperature
- Minimize exposure to oxygen
How can process consistency be achieved?
By measuring and controlling inputs, process parameters, and outputs.
What should be done to ensure malt specifications are met?
Agree on a suitable malt specification with suppliers and conduct intake checks.
What equipment needs regular maintenance in the malt processing setup?
- Flow meters
- Thermometers
- Inline weighing scales
- Laboratory equipment
True or False: Regular calibration of measuring devices is not necessary in malt processing.
False
What must be monitored in the grist analysis?
Comparison of results to target values and visual evaluation of wet milled grist.
Fill in the blank: Mashing in requires the correct _______ to grist ratio.
[water]
What parameters must be measured downstream for extract efficiency?
- Differential pressure
- Flow rate
- Time
What determines the extent to which the grain is crushed in a roller mill?
Mill gap
The mill gap determines the extent to which the grain is crushed. Setting and maintaining the gap is essential for determining the particle size profile of the grist.
