By H. L. Crane and J. W. McKay Plant Industry Station, Beltsville,
Maryland
Trees of the Chinese chestnut, Castanea mollissima, are quite resistant
to the chestnut bark or blight disease. The heavy bearing of the trees
together with the good quality of the nuts produced has stimulated
planting of trees to replace those of the American species largely
killed by that disease. Although a few horticultural varieties of
Chinese chestnuts have been introduced and propagated, the great
majority of the bearing trees are seedlings. In seedling plantings
seldom do two trees produce nuts of the same size, color, and shape. All
of these nuts when properly harvested, treated, and stored are sweet and
edible and nourishing as food either raw, boiled, roasted, or combined
with other foods in poultry dressing, salads, or pancakes. Then too,
there is a big demand for Chinese chestnuts as seed for the purpose of
growing seedling trees to be planted in orchards or to be used as
rootstocks in propagating horticultural varieties. In either case, it is
often desirable to store the nuts for several months before using them.
Chestnuts are not like the oily nuts, such as pecans, walnuts, almonds,
filberts, or peanuts, that must be dried to a moisture content of 5 to 8
per cent to store well. Chestnuts are starchy nuts, containing about 50%
moisture when first harvested, and on drying they become very hard. In
experiments conducted at the U. S. Horticultural Field Station,
Meridian, Miss., it was found that the loss in weight of chestnuts
ranged from 16.2 to 30.5% when stored for 4 months in open containers at
32 deg.F., and 80% relative humidity. In an experiment in which chestnuts
were stored 4-1/2 months at 32 deg.F., they lost 18.8% in weight when stored
in burlap sacks, 3.7% when stored in waxed paper cartons with
tight-fitting lids, and 2.0% when stored in friction-top cans.
Furthermore, chestnuts on drying lose their viability and become
worthless. Chestnuts lose moisture rapidly and become subject to
spoilage due to molds and other fungi and therefore must be considered
as highly perishable and handled accordingly.
There is a great difference in the keeping quality of the nuts produced
by different trees in that some are very susceptible to infection by
molds and bacteria and spoil quickly while others keep quite well. At
Meridian, Miss., nuts from 5 different seedling trees ranged from 2 to
34% mold infection at harvest. Studies made by John R. Large at U. S.
Pecan Field Station, Albany, Ga., showed that much of the infection of
the nuts by molds occurred after they had fallen from the burs and while
the nuts were in contact with the soil. It is, therefore, essential that
the nuts be harvested promptly after they are mature.
As a general practice the nuts should be gathered every other day during
the ripening season. Burs that have split open and exposed the brown
nuts should be knocked from the trees, and all of the nuts on the ground
should be gathered up cleanly. It would be difficult to emphasize too
strongly the importance of harvesting the nuts promptly as soon as they
are mature. Prompt and careful attention must then be given to the
conditions under which they are stored if they are to remain for long in
an edible and viable condition.
After the nuts have been gathered[10] they should be held in a layer not
exceeding 1 or 2 inches deep for 3 or 4 days. It is important that they
be kept in a well-ventilated building and that the sun does not strike
the nuts during curing. After the preliminary curing, the nuts should be
placed in friction-top metal cans (slip-top cans) and the lids should
not be tight for the first month of storage. The nuts contain enough
moisture after the short curing process that the lids will "sweat", or
surplus moisture will accumulate on the under side. This will disappear
slowly by evaporation during the first month or 6 weeks of storage and
the lids may then be pushed firmly into place, making the can nearly
airtight. The containers of nuts should be held in cold storage at
temperatures of 32 deg. to 36 deg.F. While some nuts have kept quite well at
temperatures as high as 45 deg.F., the tests indicate that the nearer the
storage temperature is to 32 deg.F., the less is the mold development.
Placing the cans in an ordinary home refrigerator should prove fairly
satisfactory with nuts that have good keeping quality.
[Footnote 10: If the nuts are infected with weevils, they should
immediately be treated after harvesting with the hot water or methyl
bromide treatment as recommended by the United States Department of
Agriculture, Bureau of Entomology and Plant Quarantine.]
It is essential that the nuts be placed in storage immediately after
they have had the preliminary curing. Any delay may increase the
possibility of mold development.
In the winter of 1945-46, nuts from 6 seedling Chinese chestnut trees
were stored separately in five-gallon friction-top cans at the Plant
Industry Station, Beltsville, Md., at 32 deg.F. for approximately 6 months.
The results are given in Table 1. It will be noted that there was some
variation in the percentage of spoiled nuts in the different lots, but
the loss was small when compared with results obtained by other methods.
All of the sound nuts in these lots were planted in a rodent-proof
coldframe immediately after they were removed from storage, and from 90
to 95% germination of the seed was obtained throughout.
It is almost impossible to keep some varieties satisfactorily with even
the best of care. Because of the great difference in keeping quality of
the nuts of different varieties and from different seedling trees, each
chestnut grower should study the keeping performance of the nuts from
the different trees in his own orchard. He should save for permanent
trees those producing nuts that keep well.
The method of storing chestnuts that perhaps has been more widely used
than any other is to pack the nuts in slightly moist sphagnum moss or
fresh hardwood sawdust in boxes and place them in cold storage at 32 deg.F.
to 34 deg.F. A little less volume of packing material than of nuts is
customarily used. The correct amount of moisture may be attained by
adding 4 fluid ounces of water to 1 pound of dry sphagnum moss. There is
great danger of getting too much moisture, which will tend to cause
spoilage. If the cold storage compartment is one that has a tendency to
dry the stored material, it may be necessary at some time during the
year to open up the boxes and add a little moisture to the sphagnum, but
in most storage houses this is not necessary.
Based upon results obtained during the last 2 or 3 years, it seems
probable that the method of storing chestnuts in friction-top cans will
prove to be more efficient than other methods now in use. Tests are
under way to determine the most desirable moisture content of nuts at
the time of storage. If this can be determined the present period of
preliminary curing will become a matter of reducing the moisture
content of the nuts to a known amount before they are stored. It is
likely that other refinements of the method will be made in the near
future, but the procedure here described has given results that merit
further trial by those concerned with chestnut storage problems.
TABLE I--Record of Keeping Quality of Nuts from 6 Seedling
Chinese Chestnut Trees Stored In Friction-Top Cans At 32 deg.F.
for Approximately 6 Months At Beltsville, Winter--1945-46[11]
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Total Weight Weight of Weight of
Tree Number of Nuts Sound Nuts Spoiled Nuts Percent Spoiled
4-24-46--Lbs. Lbs. Lbs.
----------------------------------------------------------------------
7861 23.69 23.08 .61 2.57
7881 25.20 24.63 .57 2.26
7930 26.85 26.48 .37 1.37
7932 24.29 23.80 .49 2.02
7938 29.00 27.48 1.52 5.24
8174 15.82 14.80 1.02 6.45
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ALL LOTS 144.85 140.27 4.58 3.16
[Footnote 11: Weighed and examined 4/24/46.]