Brussels sprouts may be as traditional a part of Christmas as brandy butter and unfunny cracker jokes, but their transformation from growing in a field to a bag in your local supermarket is surprisingly high-tech.

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And they’re not just a Yuletide treat any more, with produce available for six months a year, says Andrew Burgess, director of agriculture at big-scale grower Produce World.  Based near Boston, Lincolnshire, and growing over 240ha of sprouts, he is in a good position to spot trends in the market.

“Demand has been growing strongly in recent years,” he says. “The health characteristics of sprouts have been latched on to by producers. We’re now harvesting them from August to March.” 

Raising the plants in greenhouses starts well before Christmas, with planting-out taking place from March to May. Achieving a long stem by July is crucial to producing a yield of up to 20t/ha.

Produce World uses up to eight different varieties to achieve continuity through the season.  When sprouts are at just the right maturity their leaves drop off the stalk, which makes harvesting much easier. However, erratic weather can make this target difficult to achieve.

Christmas rush

Despite the longer selling season and overall growth in the market, Christmas still accounts for the bulk of sales. These increase by 400% in the two weeks before Christmas as shoppers start getting in supplies for the most important lunch of the year.  

Sprouts don’t store well, so matching supply to demand is tricky. “At Christmas we are working flat out harvesting on a 24-hour, 7-day basis,” says Mr Burgess. “The harvester’s lights are so powerful it looks like a moving Christmas tree.”

Technology at a price

In the past, sprouts were harvested by tractor-drawn machines, with cutting, feeding in and sorting all done by hand. However Produce World now runs two harvesters built by Dutch company Tumoba. 

The company’s most recent purchase is a four-row self-propelled harvester that runs on tracks. Four operators feed the stalks into a trimmer, which automatically adjusts to the width of the stalk. Then a series of rotating knives cut the sprouts from the stalk.

Angled conveyors transport the sprouts and help remove unwanted trash. Then an optical sorter identifies sprouts that are off-colour or of poor shape and an air jet swiftly pushes them out, allowing them to fall back on the field. The cleaned veg are delivered into a tanker that holds 7t. Average output is a speedy 1.5t/hour.

This sophistication comes at a price, though – the cost of this machine is more than £230,000. Amazingly, Tumoba produces an even larger six-row harvester and also has a rival in the form of Belgian maker Deman.

The combination of tracks and a large tank reduces the need for tractors and trailers to enter the field, reducing the damage to soil structure. The harvester deposits the sprouts into one tonne boxes or bulk trailers  which are taken to the packing plant. There, they are either dispatched immediately or stored at 2˚C for a period of up to 48 Hrs.

Operators steer the cutting heads with their feet and each head can also be adjusted for height. The stalks are fed into strippers that look like giant rotating pencil sharpeners. The sprouts, meanwhile, fall on to a moving cross-belt and then another belt delivers them to the tank.

While the machine is in work it is controlled by the operator on the right hand side. When the tank is full the operator moves on to the platform at the rear to get a better view.

After the crop has gone

Steel tracks are the one thing that sprout and sugar cane harvesters have in common. However, there the similarities end as the mud of a Lincolnshire sprout field could not be more different from the hard, dry conditions of a cane plantation.

The need to harvest crops in the wettest months of the year rules out the use of rubber tracks, which would simply slip too much. The machine is transported between fields on a triple-axled low loader hauled by a tractor.

Contract growers such as Produce World have to return the field to the farmer in the same condition that they received it, which typically means ploughing. After the sprouts are lifted the field will typically be sown with a spring crop such as cauliflower or broccoli. For post-Christmas ploughing a hard frost is always welcomed, though 2014 and 2015 (so far) have been notably short of them.

The machines are completely stripped down after each harvest. Growers tend to hold on to them even once they have been replaced, so they end up with quite a collection, says Mr Burgess.

Broccoli gets mechanised too

Produce World also grows broccoli throughout the year, thanks to being able to produce the crop in both the UK and Spain. It uses a specialist broccoli harvester-cum-mobile packhouse built by Lincolnshire manufacturer Vegetable Harvesting Systems, which is accredited by the British Retail Consortium. 

The broccoli is cut by hand, put on to a series of cups on a moving conveyor and then delivered to the platform. There, it is weighed, shrink-wrapped and priced. From knife to ready-to-sell pack takes just 60 seconds and up to 50 pallets a day can be harvested, a total of approximately 20t or 60,000 heads.

The harvester has been designed to fold up on to a lorry and be shipped down to Spain once the UK season is over. This helps to maximise productivity from the £570,000 investment. Transport from the field is carried out using refrigerated trailers to maintain product quality before being dispatched from the factory.