Who this is for
- A grower moving from selling at the silo to storing and milling their own crop.
- A mill that keeps running out of feedstock in the third quarter and buying it back at a worse price.
- A co-op or aggregator whose intake queue is longer each season than the last.
- Anyone who has been quoted a sheller and a silo as two unrelated line items.
The burst and the flow
A maize harvest does not arrive at the rate a mill eats. It arrives over a few weeks, wet, at whatever hour the trucks turn up, and then it stops for a year. Every piece of equipment between the field and the first mill roll exists for one reason: to turn that burst into a flow the mill can meter.
That reframes the whole sizing question. The yard is not a set of machines each with its own capacity number to be maximised — it is a chain in which one link is always binding, and the binding link is almost never the one on the quotation. Shell faster than you can dry and you have built a queue of wet grain. Dry faster than you can move it and the dryer waits on an auger. Store more than you can sell into a rising market and you have paid for a warehouse to watch a price fall.
The failure we see most often: the sheller is specified first, because it is the machine with the most impressive number; the dryer is then sized to match the sheller; and the silo is sized to hold the harvest. Three decisions, each reasonable on its own, compounding into a yard that can process grain it cannot dry, into storage it cannot justify.
What each stage is actually sized by
Four stages, four different governing numbers. None of them is “tonnes per hour” on its own.
| The stage | The number that sets it | What goes wrong if you size it the obvious way |
|---|---|---|
| Intake and shelling | Hours the yard can actually run per day during the harvest window | Sized to the field’s peak day, you buy a sheller that idles eleven months and still cannot clear a wet queue |
| Drying | Tonnes per hour times the moisture points to be removed | Sized to a nameplate tonnage, the dryer that comfortably takes two points out stalls when the crop comes in five points wetter |
| Storage | The marketing window you intend to sell into | Sized to the harvest, you own a silo you fill once and empty once — at the year’s worst price |
| Handling between them | The slowest link it feeds, not the fastest machine in the yard | Sized to the sheller, augers and elevators quietly become the constraint nobody budgeted for |
Why “how many tonnes an hour” is the wrong first question
A dryer does not have a capacity. It has a capacity at a moisture differential. Removing two points of moisture and removing five is not the same job on the same machine, and a quotation that states only tonnes per hour has told you nothing you can plan with. Ask instead: at the moisture my crop actually comes off the field at, and the moisture I need to store at, how many tonnes an hour does this dryer clear — and what does that do to my fuel bill per tonne?
That single question reorders the yard. Once the dryer’s real throughput is on the table, the sheller stops being a headline and becomes a consequence: there is no point shelling faster than the dryer can take it, because wet grain in a heap is not inventory, it is a loss event with a date on it.
What the grading regulation fixes, and what it leaves to you
“Dry enough” is not a matter of judgement in South Africa. The grading regulations made under the Agricultural Product Standards Act set the permitted moisture content for graded maize and — this is the part that matters for equipment — prescribe how moisture must be determined: to the tolerance of a stated moisture-meter class, against an oven-drying reference method. So the target is a legal number measured a legal way, not a number your operator forms an opinion about at the intake point.
What the regulation does not do is tell you how to hit it. It fixes the destination; the dryer, the fuel, the residence time and the intake discipline are yours. Two practical consequences follow. First, a calibrated moisture meter at intake is not optional instrumentation — it is what makes the rest of the yard auditable. Second, the grading standard is the number your dryer must be sized against, which is exactly why “moisture points removed” and not “tonnes per hour” is the specification you should be buying.
Where this sits next to the mill
This page deliberately stops at the first mill roll. If the question on the other side of it is how large a mill the same crop should feed, that is set out separately in maize mill sizing at 30, 60 and 240 t/day, where storage capacity appears again as one of the dimensions that moves with mill size. The two decisions are usually taken months apart and by different people, which is precisely why yards end up with a mill that a silo cannot keep fed.
Read together with agricultural processing lines, the pattern is the same in every grain project we are asked to price: the equipment list is the easy part, and the sequencing is where the money is made or lost.
What size grain silo do I need?
Work back from the months you intend to sell into, not from the tonnage you will harvest. Storage that is filled once and emptied once in a season is the most expensive way to own grain; storage sized to let you sell across a price curve is an asset. Add a realistic allowance for the grain you will not move on schedule.
How is a grain dryer sized?
By tonnes per hour at the moisture differential you actually face — the points of moisture that have to come out between the field and the storage target. A dryer rated for a two-point reduction clears substantially less grain when it has to take out five, so a tonnes-per-hour figure quoted without a moisture differential is not a specification.
Should I buy the sheller first?
Last, not first. The sheller is bounded by what the dryer can take; shelling faster than you can dry converts a throughput gain into a heap of wet grain. Size drying and storage, then buy the shelling rate those two can absorb.
What moisture content does South African maize have to be stored at?
The grading regulations under the Agricultural Product Standards Act set the permitted moisture content for graded maize and prescribe the measurement method — a moisture-meter class with a stated tolerance, referenced to an oven-drying method. Read the current regulation for the figure that applies to your grade, and calibrate the meter you measure with against it.
Can intake, drying and storage be bought as one project?
That is how CISH prices it. The reason is not commercial convenience: the three numbers are mutually dependent, and a yard assembled from three separately optimised quotations is how the binding constraint ends up somewhere nobody planned. One specification, one commissioning target, one party answerable for the throughput.
Have a crop and a milling plan, and no idea which number to fix first? Send us the moisture your crop comes off at, the tonnage, and the months you intend to sell into. We will tell you which of the four stages is binding before anyone quotes a machine.