Pear Maturity Indexes Used to Time Harvest Date
ManuscriptPear maturity indexes are rather elusive. Those that are similar, or the same as apples, historically do not give the same consistency as apples for different years or for different orchards. The exception to this is firmness and possibly days from full bloom (DFFB). This creates a dilemma, since research and the fruit industry tend to feel more confident in making harvest decisions based on several indexes.A discussion and review of the pear maturity indexes does bring to light changes in fruit that do occur and that can be measured or observed. The fact that scientists can't predict when these changes occur, and at what rate on a consistent basis, may be actually irrelevant if firmness and DFFB are adequate guidelines. Understanding these other indexes and how they change should better fill in the pear maturity picture as it develops.
Days Following Full Bloom
Days following full bloom (DFFB) can give an approximate harvest date, at least a "ball park estimate." The difficulty occurs in the inconsistency between years. For Anjou the range can be from 120 to 150 days, for Bartletts 110 to 133 days, Bosc 130 to 145 days, and for the new Asian varieties 112 to 150 days.
Heat units accumulated 6 to 9 weeks after bloom can help predict maturity and harvest date. This system is actually quite accurate for estimating maturity several months before harvest if the weather cooperates and if temperature can be accurately measured at specific fruit blocks. As in many other temperature based models, this model uses a base of 45°F and accumulates heat units as the temperature rises above this point. This model is most reliable for Anjou. With Bartletts you must consider the occasional occurrence of premature ripening.
In pears, fruit firmness is probably the most reliable indicator of maturity. Marketing strategy plays a role in determining where in the range of firmness you'll harvest pears. Those destined for immediate shipment or short-term cold storage are typically harvested at the lower end of the range. If your plan is for longer CA storage and late marketing, harvest when fruit firmness is at the upper end of the pressure range. The recommended ranges for firmness measured by a pressure tester follow:
- Anjou: 15 to 13 pounds
- Bartlett: 17 to 15 pounds
- Bosc: 16 to 14 pounds
Fruit firmness is not a good indicator of maturity for Asian pear varieties. These varieties are best when ripened on the tree where fruit pressures will run 8 to 12 pounds. Color and taste are better maturity indexes for Asian pears when you're dealing with fruit pressures this low.
Fruit SizeAlthough there are very good predictive models for fruit size based on early season temperatures and fruit size at an early growing stage, these are not good indicators of maturity. Small fruit about 60 days from full bloom will usually remain small at harvest whether approaching maturity or not.
Soluble SolidsAmount of soluble solids has been an old standby for fruit maturity for many years. It does increase as maturity approaches and for pears ripened on the tree, like Asian pears, it may have some value. In Asian pears I'd recommend at least 12% soluble solids at harvest. On pears picked for storage, however, soluble solids are not a good maturity predictor due to variability between years, orchards, and even within the tree. The percent of soluble solids does play a role in stored fruit quality. I'd recommend a 10% minimum to obtain the best fruit quality and to help prevent freezing injury during storage. For Bartletts, 11% is probably ideal.
Acid levels in fruit affect taste and flavor but are a poor prediction of fruit maturity. Levels change yearly and usually also vary between orchards. For one sample in 1979 for the period of August through September, acid levels for Anjou started at 6.2 meq/100 mL juice and went to 4.9 meq/100 mL juice. For the same year and period Bosc started at 4.1 meq/100 mL juice and went to 2.2 meq/100 mL juice. In 1980, for the period of July through September, Anjou started at 5.3 meq/100 mL juice and went to 3.5 meq/100 mL juice, Bosc 7.8 meq/100 mL juice to 3.3 meq/100 mL juice. Complicating the picture for Bosc was an alternate bearing situation--the light crop appeared in 1980. Bartletts share the same problem. In 1980, August 6 acid levels were 6.3 meq/100 mL juice. On August 25 they read 5.2 meq/100 mL juice. There isn't enough difference here to use acidity as a maturity indicator. The only conclusion to draw is that higher acid levels do positively affect taste and therefore, should improve quality and marketability. Where those optimum acid levels are is not known. Perhaps in Asian pears where flavor is one of the better maturity indexes, acid levels could be used
StarchIn some districts, fruit starch levels may be a reliable maturity indicator. In many districts, however, the yearly variation in starch levels is too great for reliable predictions. In districts where starch level is a reliable indicator, harvest fruit when 60X of the maximum starch content remains.
Skin ColorAlthough quite subjective, fruit color can be a valuable maturity indicator, particularly for Bartletts picked for immediate sale, and for Asian pears. Russet Asian fruit changes from green to brown to orange or gold. Yellow Asian fruit changes from green to light yellow; green varieties change from grass green to light green to yellow green. Some of the green Chinese varieties remain green. In Bartletts, look for a change from green to a white-green, blotchy appearance at the fruit neck and finally a light yellow. Any pink coloration at the calyx end probably indicates a premature ripening problem in Bartletts. For Anjou, look for a change in ground color.
Skin FinishFruit finish is another subjective maturity indicator. The russetting characteristic is necessary on some varieties like Bosc and some of the Asians. For Anjou and Bartlett look for smooth, waxy skin. As fruit matures, corking of the lenticels is related to fruit finish. Immature fruit have white lenticels that become brown and shallow as they develop. The brown color in lenticels is a good indicator that the fruit will ripen without shriveling.
Fruit MoistureSome pear growers, after years of experience, can determine maturity by looking at cut fruit. They basically look for a moist cut surface rather than a dry one. Presently there is some data being developed to measure juice yield from a given amount of fruit that may provide a better idea of how effective this indicator might be.
Optical DensityChanges in optical density is a nondestructive method of estimating fruit maturity in all pear varieties. It is fairly accurate and reliable. Optical density decreases as fruit matures. Since this indicator has not given any better estimate than fruit pressure and is more expensive to do, it has not been developed to its full potential. It could be very useful in segregating fruit lots for various storage regimes.
Seasonal Temperature VariationsSeasonal and cultural effects play a role in all of the indexes discussed. In cool seasons you can expect reduced size, acid, and soluble solids. Also expect the harvest period to be shorter, since fruit pressures will drop more rapidly and storage life will decrease. A warm season should give better storage quality fruit plus better size, acids, and soluble solids. Also expect a longer harvest period, since fruit pressures drop more slowly. You can't expect fruit from trees in low vigor to advance their maturity according to these general guidelines either. Fruit grown under these conditions and from trees carrying a light crop load will usually have advanced maturity.
Maturity is Important to Storage Success
Finally, why is all this important? It's important because maturity and, consequently, harvest date affect some very important bottom lines like fruit quality, marketability, and grower returns. Fruit that is harvested too late reduces storage life and at the same time increases the chance of storage problems like senescent scald and pithy brown core. Also expect higher cullage and poorer fruit texture. If you wait too long to harvest Bosc pears, they may drop and you won't have any pears to harvest.
On the other hand, harvesting too early reduces tonnage and pack-out. Also expect high cullage and poor fruit quality in storage under these conditions.
All of these problems with improper harvest timing show up finally in grower and shed returns. By using a few of the best indexes like pressure, days from full bloom, and heat units, and understanding how some of the other indexes change as fruit mature, you should be able to properly time pear harvest for maximum storage and market potential.
Further InformationFor Further Information, Dr. Paul Chen, Oregon State University has discussed Maturity and Storage of D'Anjou Pears in the August 1983 (Vol 1 No. 3) edition of this newsletter.
Paul J. Tvergyak, Area Extension Agent, WSU Cooperative Extension.
Post Harvest Pomology Newsletter, Vol. 3, No. 3