The modern consumer increasingly demands an apple of impeccable quality that has the optimum appearance, texture, and flavour. While Australia’s apple growing regions provide some of the most ideal warm, dry conditions to deliver this quality, there is an increasing call to do more toward managing orchard harvest maturity, particularly as one means to improve consistency of eating experience.
At APAL’s recent Post Harvest Seminar participants were given one retailer’s experience of the most commonly rec eived consumer complaints about apples. These were, ranked from highest to lowest frequency of complaint; ‘not fresh’, ‘bruised’, ‘soft’, ‘brown centre’, and ‘not good taste’. As one consumer wrote “how do we get some consistency in the flavour, taste and texture of these apples? At the moment it is potluck as to what we are sold.” This damning message was consistent with the wider call for a greater focus on eating quality and consistency.
Since 2006, APAL’s Future Orchards® project has helped drive the apple industry towards the modern intensive orchard system. The fundamental aims of intensive systems are to boost yields per hectare, increase per cent Class 1 packout, allow more rapid switch to new varieties and increase overall productivity. A significant parallel benefit is improved consistency of production as many of the orchard factors are improved, especially with fruit size and colour, which ultimately leads to less variable maturation than before. Examples of these orchard factors affecting maturity are crop load, rootstock, pollination, soil type, seasonality, latitude, altitude, orchard aspect, position on tree and tree health.
APAL’s Future Orchards® 2018-19 program has been addressing the importance of quality and ensuring we deliver to our consumers a great eating experience every time they eat an apple or pear. Improving quality is a key priority for growers and the wider industry and seen as critical to the success of the long-term goal of boosting consumption.
All in the timing
In many cases, poor eating quality can be attributed to fruit being harvested either too early or too late and then being stored inappropriately, causing the development of undesirable characteristics.
Apples, as a climacteric fruit, can be harvested less mature to then be stored as they continue to ripen until reaching the consumer. The early-harvested fruit which has reached a level of maturity where it has the capacity to ripen has more capacity for long-term storage when compared with late-harvested fruit. Often, however, the market gets this wrong because they want the fruit early for immediate consumption. So the fruit is regarded as commercially mature when it is not yet physiologically mature.
For the consumer, apples picked too early will generally be too firm, starchy with lower sweetness, tasting sour, and acidic. This is because aldehydes predominate in immature apples giving a taste that resembles cut grass. On the contrary, apples picked too late will be a soft mealy texture, off flavours, lenticel spots and greasy skin. As the apples mature and ripen the aldehyde content decreases, while esters and alcohols increase resulting in the dominant flavour of fruity and sweet.
Many stages of fruit growth and development contribute to uniformity; however, the timing of harvest is one of the most essential components for ensuring consistent quality and storage life post-harvest. Historically the industry has placed a lot of emphasis on measuring harvest maturity indices as a basis of harvest timing as well as determining appropriate storage, marketing strategies, management for storage rots and physiological disorders.
Example of starch pattern index being measured using iodine solution with each apple rated from 1 to 6. These tests as well as pressure, soluble solids, colour, and taste can all be done in the field as shown, or by taking fruit back to the lab.
Measuring maturity – more ways than one
For apples there is no one measurement to determine harvest date. Instead a number of measurements are collectively used as part of an orchard maturity program. Under such programs growers are measuring the rate of change of several harvest indices, the three most common of which are: starch pattern index (SPI), firmness, and soluble solids concentration. Other measurements might include colour (background/foreground), flavour assessment, seed colour, waxiness, water core and titratable acidity. Ethylene is regarded as the only true test of maturity, others are harvest indices, but in general ethylene is used more for research purposes than commercially.
New technologies such as the DA (Difference of Absorbance) Meter measure the chlorophyll content of the fruit skin independent of the red blush. NIR (near-infrared), available as handheld or grader devices, can provide information on dry matter content, soluble solids concentration and colour.
With all these harvest indices consideration must always be given to extraneous factors such as storms, heat waves or labour shortages, all of which have a role in influencing harvest decisions.
Timing harvest should be done through measuring these harvest indices at least weekly in the lead up to expected or historical harvest date and again at the date of harvest. It should ideally be done at a consistent time of day.
Maturity parameters
Starch pattern index (SPI) is a key parameter in determining actual ripeness and storage potential of apples. The test provides an indication of the amount of starch (amylose) which has converted to sugar and as such advanced ripening, which also corresponds with increasing ethylene status. The SPI works by identifying the distribution of starch in the fruit tissue which appears when iodine solution reacts with the starch. The iodine creates a black stain in distinct patterns which are matched against a standard 1-6 SPI rating scale for the apple variety with rating 1 being too immature to 6 being tree ripe.
Soluble solids is an indicator of sweetness crucial for consumer acceptance, measured using a refractometer. While sweetness will increase during maturation and ripening it is more a quality measure, rather than a maturity measure, but still useful part of the consideration.
Fruit firmness is determined by a penetrometer which is a device that measures the force required to break the parenchyma cells in the cortex. Firmness is a way to indicate the texture and maturity. As apples mature reaching their full size, the firmness will decrease, which in turn increases the juiciness, and if they become overripe will be mealy.
Well-timed harvest
Providing the customer with consistently good quality fruit starts at the orchard. Good post-harvest management can do little with fruit the quality of which has been compromised by being harvested too early or too late. There are a range of scientifically-valid maturity measurement methods to support harvest timing, marketing and storage decisions. Maturity management at harvest ensures the fruit is picked at it’s optimum to maintain quality, prevent the development of physiological disorders and deliver a better eating outcome for the consumer. There are a range of in-depth resources on maturity available developed both in Australia and overseas, where benchmark values are provided for the more common varieties.