A Personal Walnut Harvesting Story – Nelson Hubber. (more or less in the order that it happened)
This story is told in the hope that it may be of some use to those of you who are going through the process of improving and upgrading walnut harvesting and drying equipment. These notes were originally prepared for a NZWIG field day and they’ve been added to over several years.
Bedroom. Believe it or not we dried our first walnuts in a bedroom. (Very proud I was)
DryingRacks Then came the drying racks. We have a very warm sunny place to put them. In recent years birds have become a big problem, they even try to carry nuts off the racks.
Big capacity but simple washer
It was obvious that any kind of large scale harvesting system would pick up rubbish as well as nuts so I built a washer that could handle it. To my mind the washing equipment comes before the harvesting equipment. You have to have an idea of what sort of harvester you’re going to have and once you know that you have to have a suitable cleaning and washing system in place before you get the harvester. Ours is made from a 1800 litre reject plastic tank. It has baffles to slow and control the speed at which the nuts travel through, rather than an archimedes screw, and a water blaster to make a good job of the cleaning process. I noticed that the action of the nuts rubbing against each other in the basket rollers was very helpful in removing bits of dried hulls etc so I tried to duplicate the process in the washer. (and also in our harvester)
Like almost everyone else we used basket rollers for our first harvests.
I thought that a small Rousset three wheel harvester like this would be suitable for us but they stopped making them and I didn’t put much effort into trying to find a second hand one. Rousset have decided to reintroduce a similar model and it will be coming out soon I think. This seems to be a suitable size for our orchards.
Harvesters that were tried out.
Tried out various harvesting systems and decided to build a harvester based on a Bag A Nut spiky roller because it was the most likely one to successfully work first time off. (Which it did) I remember that my heart was in my mouth when we tried it first. As soon as they are picked up the machine starts cleaning the nuts in the white tube on the side.
Harvester that I made.
Photo on the right shows blowing system that was added. This blows leaves away in front of the machine and when the duct on the side is lowered it blows nuts away from around the trees.
We harvested between 9.5 and 10 tonnes with this machine this year. (2017) It works best when the orchard is mown and flat. This year some nuts did get stuck in the soft ground and longer grass and consequently it wasn’t able to pick them up. In the 2016 season it was the leaves at the end of the season that were the problem.
We have about 900 trees and I think this machine will continue to be adequate for our needs. Generally it works well.
The first box. During a harvest I borrowed a blower off our son and quickly built a box to surface dry the nuts before they were bagged and dried at SST. I drilled holes in plywood for the bottom grille.
The drying boxes got bigger and better.
The built in drying boxes, below, have mesh bottoms and air is blown in from the barn or cycled through the drying shed. The barn tends to collect solar energy and be warm and dry. In the 2016 season we dried about 4 tonnes right down the the requirements of the factory using only warm ambient air from the barn. In the 2017 season there were only 3 afternoons in April that were dry enough for this to occur. (65% or better humidity)
For the 2016 season we had 2 drying bins and in 2017 we increased to 4.
By 2017 the drying boxes looked like this.
The left picture shows how the drying bins tilted up to make it easier to get the nuts out. In this picture there’s still another bin to come.
The idea of lilting bins was abandoned and now the bins are interchangeable and shifted around on a wheeled pallet jack.
The right picture is a diagram of the air flow.
These bins have expanded metal mesh floors so that the air flows through the nuts.
Centrifugal carpet drying fans
We have 6 of these fans from 3 brands, There are orange ones from Fanwarehouse (online) deliver the most air and are the cheapest but are the noisiest. The yellow German ones from Accurate Instruments are the quietest and most expensive. The blue ones are from Topmaq. (online and in ChCh). Pice for all is in the $400 to $500 (incl) range each.
Centrifugal fans are required to force the air through the nuts. Axial propellor type fans stall more easily when pressure is required.
Four of the fans are used to supply air to the drying bins, one for each bin. The other two are used for ambient air pre-drying.
2017 Season 2 mobile bins
Two additional bins, identical to the drying bins, were also made for the 2017 season. These were used for;
1/ Collecting nuts from the washer
2/ Ambient air pre-drying the nuts.
Ambient Air Pre-drying
Bins containing wet nuts from the washer are placed in a warm spot and an air chamber and fan put on top of them. This forces ambient air down through the bin and air dries the surface water off the nuts.
The air chamber and fan are taken off the bin and then it’s put into the dehumidified drying shed. Our system wouldn’t have handled the wet 2017 season without pre-drying, it reduces the amount of moisture that gets into the drying shed.
This pre-drying setup dries the nuts at the top of the box first. In the drying shed the airflow is in the opposite direction and the nuts at the bottom dry first. Helps to balance the drying out.
For the 2017 harvest two Dimplex 40 litre domestic dehumidifiers were installed in the drying shed. Its important to note that the drying shed can be completely enclosed when the dehumidifiers are used. Or dry ambient air from the barn used when the humidity in the outside ambient air is low enough. (then the dehumidifiers turned off and the air exhausted out through a door)
The drying shed was kept to 22 degrees celsius or more ( most of the time ) using a domestic oil column heater.
Notes on the dehumidifiers used in 2017
The two dehumidifiers that we installed couldn’t cope with the wet 2017 season so I hired two more. A 120litre one for a week and a 65 litre one for 4 weeks. The 120 litre one was fairly useless. It’s interesting to note that if you were to buy the 65 litre one it would cost $3500 new. By itself it consistently removed about the same amount of water as the two Dimplex ones, but they only cost $1000 (incl) in total for the two. (And I could have bought two more Dimplexs for the cost of the hire)
The litre rate of the dehumidifiers refers to the theoretical amount of water they can remove in a 24 hour period at about 28 to 30 degrees celsius and 80% humidity
Using this method we successfully dried 9.5 tonnes in the 2017 season using about $1360 (GST excl) of electricity.
Changes planned for the 2018 season.
Pictures of what we actually built for the 2018 harvest
More on Dehumidifiers
The dehumidifiers that I’ve used are condensate ones that rely on air temperatures typically being between 20 and 30 degrees celsius for good performance. Below this temperature range the performance drops off rapidly.
Topmaq in ChCh have the best value 80 litre commercial condensate dehumidifiers that I know of ($1299 incl) When purchased The Dimplex 40 litre model was the largest capacity domestic dehumidifier available. ($500 to $650 incl, they are regarded as being noisy but it doesn’t matter for walnuts)
Absorption desiccant dehumidifiers are an alternative. They work much better at lower temperatures and low dew points but they cost much more for equivalent capacity.
Dehumidifiers should be of a type that can be set to turn off at about 40% humidity. I have found it hard not to over dry the nuts, especially during the night when not around to check so dehumidifiers that sense the humidity and turn off are necessary. (40% is the lowest setting on the Dimplex)
The harvesting and drying system continues to work well for us. Harvesting, washing and drying about 9.5 tonnes in each of the 2017, 2018 and 2019 seasons. Just the two of us do the work and we’ll have to think about getting help as the crop increases.
I’ll keep on modifying and improving the system. For the 2020 harvest season I intend to modify the airflow that blows leaves away in front of the harvester and put HEPA air filters on the dryer air flows to remove fungi and mould spores.
2020 Harvest Season
About 13 tonnes dried very successfully through the drying system. I didn’t get around to installing the HEPA filters and didn’t make changes to the washing or drying system.
New blower arrangement on the harvester made a better job of blowing the leaves away and leaving the nuts behind to be picked up.
2021 Harvest Season
Digital humidity meters were added to the drying system in 2021. There is one meter for each drying chamber and the meters automatically turn the dehumidifier and fan off when a predetermined humidity level is reached in the air. These woked very well and saved lots of time testing and retesting the moisture levels in the nuts. Out of over 40 drying batches only two were turned on for more drying. The meters also stopped over drying, which has been a problem in previous years.
Other Drying Systems
Other drying systems such as Brenmuhl’s shown here with the red fan or Horsbrugh’s French made Rousset drying tower should be considered.
A Nest Dehumidifying System
John and Wendy Hollings have an interesting drying system in a container.
Alan and Adrienne Robinson’s commercially made tower drier from German company Feucht-Obsttechnik. The tower is about 4 metres tall using two steel bins just over 2 metres cubed. In the base of the tower, four 2.5kw electric heaters and a large fan causes warmed air to move up the tower. There is also a gas option from the manufacturer. Washed nuts are pre-dried using carpet driers then fed into the top of the tower using a conveyer belt. Each compartment can hold 350kg of walnuts but Alan adds 250kg each time which is the amount each small storage bin holds.