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Watercore: A Maturity Problem
Watercore is a physiological disorder associated with advancing maturity in apples. It varies greatly from year to year and has been shown to be somewhat related to fruit calcium levels. However, calcium sprays do not control watercore. Unusually high amounts of sunshine and a lack of cloudy, rainy days can aggravate the disorder. It is more prevalent in highly colored or larger fruit.
Watercore develops when the spaces between the cells in apples become filled with a sugar solution. This changes the look of the flesh, giving it a water-soaked, glassy appearance. In unaffected fruit the spaces between the cells are filled with air, giving the flesh a normal appearance. The sugar solution builds up in the fruit because as the apples mature, their carbohydrate metabolism changes and the interconversions between sugars and starch change.
Slight watercore does little harm to apples and, in fact, some consumers like the added sweetness. Slight to moderate watercore usually disappears in storage and no harm is done to the fruit. More serious watercore may retard the gas-exchange properties of fruit to the extent that internal breakdown develops in the cells of the affected parts.
Controlling economic losses from watercore rests with the grower's management skills. The extent of watercore is only one factor to be included in harvest management decisions. Orchard blocks with a history of watercore should be harvested before other blocks. Special marketing arrangements for watercored apples may be required.
There is no easy solution to sorting watercore. Agricultural engineers from Washington State University have developed a system of sparging air into water flumes that transport fruit. Sparging changes the specific gravity of the water. Since watercored fruit have a higher specific gravity and do not float like normal apples, a shunt or horizontal partition in the flume can be used to separate watercored fruit as they flow through the flume system.