Measuring internal maturity of citrus

Page last updated: Wednesday, 18 March 2020 - 8:06am

Measuring internal quality of citrus prior to harvest is vital to ensure fruit reaches the market with eating qualities acceptable to most consumers. In Western Australia growers have the option of testing their own fruit or sending it to a laboratory.

Minimum standards are regulated in Western Australia and National Citrus Quality Standards have been developed by the peak citrus industry body Citrus Australia Ltd. It is advisable to check with Citrus Australia or your local citrus industry body to confirm the current industry standards prior to testing.

Preparation

Collecting a fruit sample

When collecting fruit for testing it is important that the sample represents what you will be harvesting. For example if you plan to select pick mandarins, collect fruit of the same size and/or colour that you will be picking. If you are strip picking collect an even mix of fruit of all sizes and colours on the tree – be sure not to only pick the fruit that is most coloured.

Regardless of whether you are select or strip picking you must collect fruit from all sides of the trees as well as inside the canopy. Fruit samples should not have any rots, splits, puncture marks or other defects which may influence fruit quality.

It is important to consider variations within your orchard when collecting a sample.  Separate samples should be taken from each block or patch if the variety, rootstock, tree age or soil type is different – because all these things will have an effect on fruit quality and maturity. The topography of a block can also effect maturity, especially if there is a significant slope.

Collect a minimum of 10 fruit per variety/area to be tested and ensure that samples are accurately and securely labelled. The more fruit tested the more accurate the test will be.

Equipment and chemical suppliers

Many suppliers can provide the necessary equipment and chemicals for maturity testing on citrus. These can be located in the 'Laboratory Equipment &/or Supplies' section of the Yellow Pages® or on the internet.

Fruit testing equipment
Left to right, from back: digital scales, 2L beaker, sieve, 1L volumetric flask, 0.1 Normal sodium hydroxide (NaOH), 1% phenolphthalein indicator. Middle: juicer, 1L beaker, 100mL beaker, refractometers. Front: 50mL burette, knife, 10mL pipette and pump

Equipment required to carry out testing

  • 50mL auto-fill burette with a 1L squeeze bottle
  • 10mL pipette and pump
  • 0.1 Normal sodium hydroxide (NaOH) solution
  • distilled water
  • 1% Phenolphthalein indicator or a pH meter
  • good quality scales with 1g graduations
  • fruit juicer, juice only — no rind
  • fine mesh strainer
  • 100mL conical flask or 100mL beaker
  • 1 to 2 litre jug or beaker
  • refractometer (digital or hand-held prism, temperature compensating) 0-32% range.

Contact information

Kevin Lacey
+61 (0)8 9368 3546