Milling malt the correct way is crucial to the brewing process; mess it up and you’re going to see issues from mash tun to finished beer. Done right every time, your mash is going to be consistent which makes for consistent beers.
This article is aimed at brewers, quality managers and brewery managers who want to understand the art and science of milling malt, and when you should graduate to owning a mill and doing it yourself.
We will also be covering when is the right time to move from bag malt to owning a silo and what the costs involved in this considerable investment are.
If you’d prefer a more visual approach to this subject then please consider watching our milling webinar.
Before the malt even reaches the mill it needs to be in the best possible condition for milling. This means it can’t have deteriorated in storage. The major enemies of malt are pests and moisture, and by association, temperature. For packaged malt in one tonne bags or the more common 25kg (50lb) bags, we always recommend storing the malt off the ground on pallets to prevent pest ingress and to allow a free flow of air under the stack. The room in which malt is kept should be proofed against pests so a system of pest control and prevention is critical to your Good Manufacturing Practices (GMP) and should be incorporated into your HACCP, SALSA or BRC system.
Sudden changes in temperature and humidity will degrade malt quality, but if you keep the malt in a dry, relatively temperature stable environment, then it should keep its quality to the best before date on the bags.
We know that every brewery has that quarter bag of black malt in the corner of the malt room, which is fine provided that it is sealed up with a cable tie.
Remember that malt bags are not moisture proof. They are designed to have a certain amount of breathability to ensure moisture doesn’t gather in the bag (which can lead to mould formation) so having a malt stack in the brewery next to the person in charge of the washdown hose is never a good idea.
Similarly, if your brewery is located in an inclement area then don’t leave a pallet outside in the rain. If this does happen, get it inside as soon as possible and break down the stack, wipe the bags and restack, or the corners of the bags at the shrink wrap and the bottom layer will almost certainly see moisture pickup.
For silo storage, ensure that the silo is sealed up before first filling. We’ve seen silo installs where the mastic around joints and the top hatch weren’t adequately sealed and moisture started to build up in the silo resulting in mould and clumping of the malt. It is advisable to move malt every few months. If you have a silo and you’re not doing this then it might be advisable to get smaller deliveries to the brewery. Silos should have smooth walls with hopper bottoms making it easy to remove the grain. They should be emptied at regular intervals to maintain stock management and traceability.
Keep malt storage areas clean and tidy. When you start seeing webbing, that’s not spiders; it’s most likely flour weevils; the most common store cupboard pest globally and they can make a mess of your grain. Just like in the brewery, cleanliness is next to godliness.
On the subject of pests, if whole malt was left open on the floor next to milled malt I suspect the pests would go straight for the milled malt as it will be easier for them to eat – less chewing. It’s a bit like taking the drive-through at the fast food place. The drive-through is easier as you don’t need to get out of the car. In the bags, the pests don’t know the difference. A bag of whole malt next to a bag of crushed malt is a 50/50 choice for them. Good hygiene is the best way to control pests.
The topic of malt storage is wide ranging and there is a lot to think about, which is why we’ve written it all down in one handy Crisp Guide to Malt Storage.
It’s all too easy to get lost in analyses, Best Before Dates and batch codes. If in doubt, taste the malt! As part of a taste panel we recommend incorporating regular malt tasting. Getting the panel to munch the grain from the bag is better than nothing, but a kettle test can reveal deeper problems to do with off flavours and aromas. To carry this out take 200g of grain and place in 500ml of boiling water and leave for 15 minutes. Sieve the grain away and assess the aroma and flavor of the remaining liquid.
Atmospheric grain dust carries with it a risk of explosion. Legislation places duties on employers to eliminate or control the risks from explosive atmospheres in the workplace. The basics of these regulations are fairly common sense. Within the brewery, don’t allow malt dust to accumulate, ensure ducts and conveyors are well sealed to prevent dust leakage and use dust suppression if you’re blowing malt through pneumatic systems. Incorporating Preventative Maintenance (PMs) of malt handling equipment into your weekly and monthly task sheets will drive compliance.
In some countries, legislation requires you to classify areas where hazardous explosive atmospheres may occur and segregate them into ‘ATEX’ (explosive atmosphere) zones. This might be in the inside of the mill, the mill room or the entire dry goods handling area of the brewery, depending on your size. You may need to install “intrinsically safe” light fittings, switches, emergency stops, etc. in these areas. It’s always advisable to carry out risk assessments for these issues with a trained professional to protect your team, prevent injury and comply with insurance.
Additionally, malt dust can have an effect on health. Long term effects on mucous membranes of those who inhale malt dust has been well documented. This is best achieved by control measures to limit exposure to malt dust which may include using the correct grade of Personal Protective Equipment (PPE). Always carry out a risk assessment for your specific circumstances and consult the relevant legislation in your own country.
You’ll see from our packaging flow diagram we take malt cleanliness very seriously. We employ the use of rare earth magnets to prevent any metal particles passing through our packaging line. We remove small, broken or undersized corns using our malt dresser. This new fluid bed dresser is able to remove small stones that have the same dimensions as malt kernels but are removed because they have a different density. We also remove malt dust that has accumulated during the transfer process from silo to the packaging line; this ensures that whole malt arrives with the customer scrupulously clean.
If you have your own malt dressing systems they should be designed to remove:
Malt dressers come in several forms depending on their function:
We’re finding that craft breweries installing bulk malt handling systems are foregoing the purchase of malt dressing equipment as they can be a high capital cost. At the very least a bar magnet at the mill intake will protect against metal objects entering the mill and causing a spark, which could trigger an explosion in a dusty environment. This should be cleaned weekly as part of a preventative maintenance programme.
Now onto the good stuff; Milling. It’s as crucial to brewing as chewing is to eating!
The aim is to produce a grist with the highest yield of extract with the best possible run-off in the mash or lauter tun. The science is fairly basic; the smaller the particle the more extract your recover, but the run-off will be slower. In a mash-tun where you don’t get any mechanical help (i.e. lauter-tun rakes) with speeding up run-off, you need to keep the grist fairly chunky or coarse. In a lauter-tun, we can make the grist that bit finer, knowing the rakes will help move the wort through the grain if required.
In the UK we are blessed with some of the best malting barley in the world. One aspect of its “bestness” is that the malt produced from it is easy to mill. We call this friability. Friable malt is malt which is easy to break apart. British malt, due to the varieties, growing conditions and malting practices generally produce highly friable malt. In the lab we measure friability in a “friabilimeter”. For more info on this and other standard lab analyses check out our 2020 New Season Malt Guide
On the Certificate of Analysis, the friability for most malts should be greater than 90%. This is an indication of good malting practice. As a rule of thumb, friable malts are broken apart easily in the mill and produce finer grists. Therefore, they only need simple milling equipment, like a 2 roller mill. Less friable malts produce a coarser grist and require more complex milling equipment, like a 4 or 6 roller mill. They require more energy to mill them to as fine a grist as a well-modified malt. This is why when brewers switch from a malt of low friability to a malt of high friability, their mill will produce a much finer grist and as a result, extracts will increase, but this also increases the chances of poor run-off and filterability issues downstream.
Ground malt (grist) can be generally classified into three fractions; the husk, the grits and the flour.
The husk is the outer layer of the barley kernel and it forms part of the filter bed during mash filtration. A high quality mill will separate the husk from the starchy endosperm of the malt but won’t shred it. By maintaining an intact husk, a more porous filter bed is achieved.
A low percentage of husk, due to incorrect milling or the inclusion of cereals with no husk such as wheat, oats, rice and maize, will result in;
The outer layers of the malt kernel also contain polyphenols. If the husk is torn apart and shredded by the mill, this increases the chances of these polyphenols being extracted into the wort. If extracted they can:
The disruption of the grain structure is affected by direct compression on the grain and shear forces.
The grain is compressed as it passes through the rollers effectively squeezing the husk from the endosperm and breaking apart the endosperm into different particle sizes
The rollers run at different speeds and may be fluted to increase shear force.
The mill efficiency and capacity are controlled by the roller length, roller diameter, roller speed, roller gap setting & roller surface friction (flutes).
There are several types of mill and are generally referred to by the number of rollers. As the number of rollers increases so too does the cost and complexity of the mill.
On a 3 roller mill, a single roller sits below the top two rollers adding an extra step to remove the hard ends of under modified malts from the husk. All the grist falls through the third roller. Because of this 3 roller mills are more like 4 roller mills.
Adding extra rollers does not mean more extract. If you’re purchasing a well-modified ‘friable’ malt, I don’t think it would make too much difference but, as all the grain falls through the bottom roller it may harm the husk fraction and cause wort separation issues. If you are using less modified malt that has a lower friability the bottom roller will separate the hard ends from the husk and should increase extract. By how much, I honestly don’t know.
It is very important to analyse the grist that comes out of the mill to diagnose or preempt any brewing issues. At the very least, a visual inspection should be carried out, but the gold standard analysis is by using a grist fraction box or grader to calculate the different fractions of malt as described above.
Grist boxes come in all shapes and sizes, but we recommend the simple three layer box, to assess husk, grits and flour fractions. A box will set you back around £100.
Grist should be assessed by taking a representative sample from the mill (brewing mills will have a sample port to allow a sample to be taken immediately after milling) and following the procedure as follows:
Keep a note of the grist fractions on your brew sheet or in a record book next to the mill. While grist doesn’t need to be assessed every time you brew, it should be done on a set schedule and especially at the change over of season or if you change maltster or base malt type.
Collecting a “representative” sample from your grind can potentially be difficult, depending on your setup. Do you know if collecting it after it passes through your auger to the mash kettle is OK, or do larger particles travel through first? I’m sure sampling right after the mill rollers is always the best, but that’s not always easy to do depending on the mill.
As the malt travels through the auger it will mix it up potentially changing the distribution of the grits, I’m not sure it would tell you anything. In this instance measuring the grist fractions could be miss leading. Record extract, filtration times and wort clarity and if there is deviance from standard think about making some adjustments. Trial and error is probably the best way forward but it is risky so make small adjustments each time until you find a happy medium.
It’s always best to check with the manufacturer on the process for adjusting the rollers. Generally, there is a locking mechanism that needs to be unlocked and then dials turned to change the roller gap. Make changes at the minimum amount the mill will let you, this may be 0.05mm or 0.1 mm. Lock the rollers and then check the roller gap along the length with a feeler gauge. Run the next grind and compare against your target.
Grist fraction analysis and mill adjustment can seem time consuming and laborious, but it can have a significant effect on not just mashing, but fermentation, conditioning and filtration too. However, don’t be a slave to the fraction table; find the fractions that work for your kit and malt. Also measure the fractions, observe the effects of those fractions, adjust the mill and repeat. This is the classic Plan, Do, Check, Act cycle studied in quality management courses across the land; it will pay off!
Let’s start with the basics; we put the following Best Before dates on our crushed and whole bagged malt:
Firstly, it gives customers an understanding of when the malt was made – i.e. how “fresh” it is – and is it a legal requirement for foodstuffs in the UK.
However, best before dates are anything but basic. They rely on the supply chain and customer treating the goods in an ideal way throughout transport and storage respectively. If only every part of the supply chain and every bar owner treated your beer in the same way you want it to be treated! Therefore, we’ve developed a set of Malt Storage Guidelines. If followed, we believe that the malts will still be good up to and possibly even beyond the Best Before dates stamped on the bag. These guidelines apply to both whole and crushed malt.
Of the two types, we receive a lot of questions about the quality credentials of crushed malt. Given the size of the UK, our temperate climate and ease of road transport, we can ship crushed malt from our warehouse in Norfolk to all parts of the UK within a few days, safe in the knowledge that there will be no deterioration in the quality of the malt. We have carried out extensive shelf life testing of crushed malt where the bagged crushed malt was stored in our warehouse alongside the bagged whole malt from the same batch. We carried out extract, moisture and taste tests on the crushed and whole malt and found no deterioration in these key parameters over the course of 6 months. From our extensive experience in crushing malt and through customer feedback
However, as with all foodstuffs, Best Before Dates are only a guide and the storage conditions of malt will ultimately dictate how long it will keep.
One of the principal concerns customers have is how long the malt has been kept in our warehouse. You can easily back calculate this from the Best Before Dates above. On average, our crushed base malts sit on the warehouse shelf no-longer than 2 weeks and our speciality malts, no longer than 6 weeks. If you only use small amounts of a certain crushed malt we recommend purchasing just what you need from our UK homebrew wholesalers The Malt Miller or Geterbrewed, so as to ensure a fresh crush.
The above points on crushed malt apply only to the UK and to countries where we can send malt by short-haul road transport. We never ship crushed malt overseas due to moisture and temperature fluctuations in shipping containers. For whole malt in shipping containers we have found a combination of using bags of silica to trap moisture and ensuring that pallets have been dried to the correct moisture level, prevents any moisture release in the shipping container, which could be absorbed onto the bags or into the whole malt.
Our partners in the USA crush malt at the individual warehouses located throughout the country so that crushed malt isn’t shipped across the country in adverse conditions.
We also get asked about oxidation in crushed malt and many brewers believe that if you don’t crush malt fresh then it will very quickly oxidise and cause staleing reactions in the beer.
In our testing of crushed and whole malt we make up a malt tea as part of the flavour assessment. This quickly reveals the freshness of the malt in the same way a brewer would taste a force-aged sample for degradation of flavour. We have found that under the correct storage conditions, there is no difference between freshly crushed and whole malt up to xx months. We would always say, if in doubt, make a mash brew and taste the malt.
At Crisp we mill the speciality (crystals, roasted, other cereals, etc.) to a slightly coarser grist than the base malts (Best Ale, Maris Otter, German Pils, Euro Pils, Clear Choice, etc.). Coloured malts and speciality malts generally gum up the filter bed and have a negative effect on wort separation. Milling more coarsely reduces the particle size and improves the filter bed porosity helping to speed up filtration. If you mill to the same settings as your base malt and don’t have any issues, don’t worry about it.
Flaked torrefied products don’t need to be milled. During production process the cereal is subjected to rapid heating until they ‘pop’. This disrupts the cell structure as the starch gelatinises. They then pass through hot rollers. Milling them in the brewery can cause wort separation issues, they can also stick to the rollers causing blockages.
Is it wise to crush and mash wheat and Rye separately and mash early at lower temperatures to increase our malt efficient ?
Mashing wheat and rye separately may become troublesome. There will be very little enzyme activity and you will struggle to get conversion. Rye and malted wheat have smaller grain sizes than malted barley so they’re generally coarser as they pass through the mill. Added evenly to the grist, wheat at 40% and rye at 10% should pose little issues.
Having your own mill can give the brewery a lot of flexibility but there is no hard rule on when you should add one, I would ask; why do you want one?
If it’s for cost savings, the average cost of a 2 roller mill is around £7k, if you use 100 tonnes of malt per annum you will save £2k per year by not paying the crushing fee so payback is 3.5 year. You may gain some extract improvement that will reduce the payback time, but you may not, it depends how good your supplier is at crushing malt.
I would say the main reasons for adding a mill is to give the brewer control over the process, possibly make life easier by adding the bulk bag option and to build in future expansion. Moving to bulk is much more expensive with costs around £80k, you need to be using around 150 tonnes per annum before making this move and payback is still going to be over 4 or 5 years so it goes back to the question – why do you want a mill? In this case it’s for operational ease, you will most likely be brewing multiple times per day and bulk storage will save space and time.
We are really fortunate that in the UK most breweries are located close to a maltings and so we can supply bagged, crushed malts that will keep well for long periods of time under the correct storage conditions. We are also aware that this is hard to do in different parts of the world and so, no one size fits all. If your location, climate, storage conditions and/or size mean that a mill is a necessity rather than a luxury, then do some research and buy a mill that will produce consistent results, is easy to finely adjust and that treats the grain well.
Producing consistent grist on brewery-based milling equipment requires an investment in; high quality kit, quality systems, attention to detail and recordkeeping. By producing a consistent grist you are setting yourself up well for a successful mash. A poor or inconsistent grist, especially one which isn’t suited to your mashing method, can cause issues in lautering, starch extract recovery, extract of beta-glucans or polyphenols, filtration, fermentation and shelf life.
We believe that any decision to purchase a mill or silos should not be made lightly and that the investment return needs to be carefully considered and balanced with manual handling, time saved and the potential impact on extract and therefore cost of the malt.
We have helped many customers in scoping dry goods handling projects so please don’t hesitate to get in touch if you need some friendly advice about this topic. If your experiencing issues with your grist in the mash tun then do check out our troubleshooting guide.