Waxing can reduce weight loss in storage

By Melissa Hansen
There are many quality advantages to waxing tree fruit, from retaining firmness and reducing color loss to lengthening shelf life. But there is an economic advantage as well--reducing weight loss during storage of the fruit.

Although the difference in weight loss may not seem significant when comparing one apple with another, it can add up when a storage room filled with waxed apples is compared with a room of unwaxed apples.

"The amount of weight loss is a lot when you are talking about multiple bins of fruit," said Dr. Stephen Drake, postharvest researcher for the U. S. Department of Agriculture (USDA). "It is not a lot of weight loss when you are looking at an individual piece of fruit."

During research evaluating the effectiveness of fruit waxing, Drake, who is stationed at USDA's Agricultural Research Laboratory in Wenatchee, Washington, noted that waxed Red Delicious apples lost only 0.93% weight during 90 days of cold storage as compared to unwaxed Red Delicious which lost 1.34% weight in the same time period.

The difference was even more noticeable in Golden Delicious apples. Waxed Goldens lost 1.22% weight, while unwaxed Goldens exhibited a 1.75% weight loss during the 90-day storage period.

In essence, Drake said that the longer fruit is expected to be stored, the more important waxing becomes in reducing fruit weight loss.

According to the USDA researcher, waxes are commonly applied in Washington to apples and pears, and less frequently applied to apricots, peaches, and cherries. Types of waxes include shellac, carnauba, resin, and sucrose polyesters. Shellac and carnauba are the predominant types used in the tree fruit industry.

Throughout the wax research, Drake did not observe a fruit quality difference between shellac and carnauba waxes. Both types improved fruit appearance, reduced weight loss, aided in firmness and color retention, and improved packing ease.

Waxed fruit stays greener and closer to its harvest color, Drake said, in regard to Golden Delicious and Granny Smith apples that have been waxed.

Data on waxed cherries show firmer fruit, but a loss of stem color results from the waxing, he added.

Drying methods

There are some differences between the methods used in drying the waxes, either with hot air or with cold air.

Drake has found a wide range of hot drying temperatures used in Washington packing houses, from 115°F to 150°F; cold-air drying temperatures of 32°F are standard.

Waxed apples that have been dried by the cold method tend to be firmer, while drying the wax on the apples with heat increases weight loss. But these differences are very slight, Drake said, and are not economically significant.

The drying method used in pears resulted in a more significant difference, he noted. Cold-air dried, waxed pears tended to be firmer and gained an additional one to two days of color, primarily because of the additional 33 hours needed to chill the pears back to 40°F. after using hot air to dry the wax.

Drake stated that after 120 days of storage, waxed pears that were cold-dried were about 2.5 pounds firmer than waxed pears dried with heat.

Although there are color and firmness advantages to the cold-dry method, Drake said the advantages are not sufficient to offset the additional equipment and operating costs (due to the much greater amount of electricity required) of the cold drying method.

From time to time, waxed Red and Golden Delicious apples have turned white when shipped overseas to hot and humid regions. Known as wax whiting, he said this problem results when pure shellac is the waxing ingredient.

Wax whiting

Drake suggested that if cold storage operators are concerned with the possibility of wax whiting, they should conduct the following test to measure the whiting potential of wax.

Warm a piece of fruit to room temperature, then wrap a hot, moist towel around the fruit. Keep the towel heated (by pouring hot water over it) to about 140°F for about 30 minutes. If the fruit turns white, indications are that it is not a good export candidate for humid countries.