Macadamias – Harvesting for Quality

Reading Time: 7 minutes

Dorran Bungay

Macadamia farming promises a rich reward for growers – for those who get the recipe right.

South African farmers have recognised the macadamia profit potential and, today, the country is the largest producer in the world. SAMAC estimates that the 2023 season will deliver 68 840 DIS tons, an increase of 28% from 2022!

Farming, in general, has been a way of life, a cultural life style, but modern macadamia farming has become a more stressful and serious business option fraught with many risks that require multiple skills if it is to be successfully ventured.

In the early days of macadamia farming in South Africa the volumes were small and grow- ers were able to give (almost) personal attention to their harvest activity as well as take pedantic post-harvest care of their crop. In those days there were fewer orchards and less pests. Chemical considerations for all applications were not under the severe scrutiny that they are now. The market was unsophisticated and processors accepted macadamia nut- in-shell (NIS) with unsound kernel (UNSK) values of as high as 8%.

These days the harvest volumes are larger and growers need many more business skills, greater technical ability and a wider understanding of world events that affect our markets. During recent past years growers have to deal with climate change, erect more fences, deliver UNSK at values < 2%, contend with increasing energy costs and shortages … and now – in 2023 – growers and processors alike have to adapt to receiving a smaller reward for their effort in the year before.

At the recent Ambermac Expo in February. ‘23, an ABSA Economist, Marlene Louw, pre- sented an Agric Economic Overview of the future of the macadamia business in South Africa. Marlene concluded her talk with a salient sentence of a few very sober words:-

“Those who wish to succeed in the macadamia business must ‘consistently deliver high quality!”

Many processors have a ‘mission statement’ displayed prominently in their reception areas, stating that they are committed to – amongst other promises – delivering macadamias of high quality to their customers.

Is there a mission statement displayed by any processor in the world that actually defines what the quality of macadamias entail? The mission statements simply assume that their clients/consumers will know what is meant and that they will be delighted to purchase their product.

Many processors do deliver good quality most of the time and the best of them are con- stantly updating production processes to meet the sophisticated international standards of the growing sophistication of the expanding consumer base.

World wide, macadamias are marketed as highly nutritious and healthy, but that is more of a medicinal statement and alone it does not specify quality.

What is macadamia quality?

Quality macadamias require four consistent specific attributes that will determine whether a consumer will make repeat purchases:-

1. Aesthetics – they must look appealing (colour, size, damage free – insects, mould, dis- colouration – smooth & dust free)

2. Flavour – they must meet the advertised expectation of smell and taste

3. Palatability – they must have a smooth, creamy texture after a satisfying initial crunch

4. Shelf-life – macadamia products should be correctly handled and packaged to stay fresh and hygienic for 1 – 2 years depending on style. A rancid or near rancid macadamia kernel that has lost its shelf-life, is not fresh (stale) and is a bad experi- ence.

Macadamia nuts should arouse a repetitive desire in the consumer:-

“So delicious, eat some more!”

Quality determination should, therefore, be aimed at delivering “ zero defect” in all of the above attributes and not, as, the common maxim so often dictates – “ if it’s edible, its quality”.

The Macadamia Grower is the Key to Quality

Macadamia kernel shelf-life is initially determined by on-farm practices and then maintained by processors using good management and hygienic packaging practices .

The grower is the first and primary controller of quality. Quality starts with the savvy farmer. It’s about producing sound quality and then preserving the value of the harvest while sort- ing out and eliminating the defective nuts before they are delivered to the processor. 1st prize is achieved when the best quality is delivered within two weeks after harvest thereby also reducing the risk of on-farm loss and ensuring early payment by the processor.

It must be remembered that the business of the processor is to endeavour to sell every grower’s nuts to an ever increasingly sophisticated consumer who is becoming more intel- ligent about his/her culinary preferences and tastes.

The processor is not a hospital and cannot repair nuts that have been compromised by on-farm decisions and processes. Nuts that are delivered with defects and damage (un- sound kernel – USKR) will take more sorting personnel and a longer time to process, often resulting in a lower selling price.

Processors simply cannot pay ‘top dollar’ for high USKR, but will, of necessity, charge the grower more for processing a poor quality crop. In the worst of marketing times the pro- cessor will only accept nuts from those growers who have a dependable reputation of de- livering high quality with low USKR values.

The key take away point to note is that:-

“In order to stay relevant and profitable macadamia growers must buy into the macadamia quality chain to ensure both their own survival and that of the Industry”.

Preserving Harvest Quality On-farm

1. The 2023 harvest season has started very wet in South Africa and poses a huge loss risk to both growers and processors. Growers simply cannot afford to leave macadamias on a wet orchard floor – or allow them to get wet anywhere else. The nut- in-husk (NIH) is a seed that will begin to germinate as soon as conditions are right – water, heat and light. The percentage of nuts at any stage of germination will be recog- nised as defective during laboratory sampling at the processor.

2. The macadamia nut, like any other agricultural crop, is a food source for everything – mould, bacteria, insects, vermin, people. The NIS appears to be safely protected in a hard shell, but that is an illusion. The shell is, indeed hard, but the kernel is fragile, eas- ily bruised and it can rapidly decompose within days if circumstances allow. The longer the nuts (NIH) are on the ground – especially in wet conditions – the higher the risk of mould and hydrolytic rancidity (= macadamia oil in contact with water tastes and feels soapy). Mould and decomposition can rapidly occur (overnight) especially if NIH are harvested into closed plastic bags and/or stored in a vessel without adequate dry venti- lation.

3. The de-husking process can add a bruising risk to the kernel. If the pressure setting of the dehusker deforms the shell, the kernel will be bruised. A deformed shell can return to its original shape, but the kernel will have been permanently damaged. The kernel of macadamia NIS that are subjected to high impact forces (dropping) may also likewise be bruised.

4. The oil content of a mature macadamia kernel has an approximate 70% oil content that will leak from bruised cells especially under warm conditions. Oxygen, when it comes into contact with leaking macadamia oil, is absorbed and will initiate an irreversible ran- cidity process (loss of shelf-life) that composts the oil to Free Fatty Acids (FFA’s) that have foul odours and bad taste. Processors do (should) test samples at delivery for peroxide values (PV) to establish if and how much oxygen has been absorbed. PV val- ues of NIS delivered from the fam gate should not exceed 1 meq (milliequivalent) per liter. The test will determine if and how far, the rancidity process has developed. NIS with high PV values may be downgraded in the value payout or even rejected entirely by a strict processor.

5. De-husking must be done and completed on the same day of harvest. The husk is a reservoir of water that will promote both mould and germination. To preserve quality on- farm WIS should be immediately uniformly “cured’ (not dried) to between 8% mc and 10% mc after de-husking prior to delivery to a processor. The safe water activity mois- ture content value of macadamia kernel inside its dry shell is 3% mc (approx. 8% – 10% NIS mc). The processor laboratory determines the average moisture content of the kernel sample at delivery and applies the payment assessment accordingly. A high moisture content value of the sample indicates that the grower is selling water which the processor must remove at high cost. The grower will pay this cost.

6. In early season, immediately after de-husking, NIS are commonly conveyed through a water bath to detect ‘floaters’ that are unsound NIS that have no value. NIS that float are typically old season nuts that float because they are light in density – normally they will have an airspace inside the shell from cracks or created by insects. WIS with sound kernel will sink in a water bath. NOTE: The water bath is not a means nor a method of determining for NIS maturity.

7. Dry-in-shell (DIS), NIS after curing, must be properly sorted on-farm to exclude any un- sound NIS from being delivered to the processor. Growers will be penalised by obvious defects in the sample detected at the processor laboratory – those that have cracks, splits, are dark, white or discoloured, mouldy or deformed. It must be remembered that the value of the entire delivered batch will be determined by the percentage of sound quality of the sample selected. It is important for the grower to understand the Freight Evaluation Certificate (Frec) report provided by the processor so that the on-farm sort- ing staff, who are employed to ensure delivery quality (and who are empowered with good lighting), are enabled to visually detect defects.

8. Immature nuts are also a defect that is penalised by the Processor. The kernel of im- mature nuts have a lower oil content and a higher sugar content. The sugars in imma- ture kernels roast dark brown or black and are rejected by buyer / baker / consumer. Nut-in-Husk (NIH), while still on trees, should be checked for maturity – a learnt skill – before harvesting. NIH that have prematurely abscised before maturity due to wind, storm, insect, etc may inadvertently be included in a harvest round. It is of value for the savvy grower to be aware of premature nut fall event and to do an average maturity test to establish the severity of the problem if it exists. NOTE: The kernel of ‘bone dry’ mature DIS will float in fresh water due to its high oil content.

9. RECOMMENDATION: Growers should properly establish the weight of their macadamia NIS delivery to a processor before they leave the farm. It is an oversight to assume that nuts will not be ‘lost’ en route to the processor or that the mass scale at the receiving processor is always correct.

10. SUGGESTION: Growers, their families and key staff who work so hard to produce and sell their product should regularly eat macadamias of different cultivars, defects and age to understand both its value and its shelf-life limitations.

A more comprehensive explanation for growers regarding the risks and remedies of on- farm post-harvest care and delivery to the Processor can be read in Chapter 4 of the 2nd edition of:-

“Macadamias: An Overview and Guide to Preservation Principles and Engineering Prac- tice”.

Orders & enquiries to: Jen Davis – / +27 83 728 7803