October, 1959 Citrus Experiment Station 2Iiineo Report 60-10
t. Grierson and F. U. Hayward
Hydrocooling of citrus is only recoiaiended when combined with a fungicidal
treatment to reduce decay after the fruit is removed from refrigeration.
Only two fungicides approved by the Food and Drug Administration are effective
against the cor aon fruit decay organisms of Florida citrus. These are diphenyl (also
called biphenyl) and o-phenylphenol (Dowicide I) or its sodinu salt, sodium o-phenyl-
phenate (Dowicide A).
tIhen hydrocooling, the simplest and cheapest fungicidal treatment is to add
Dowicide A to the hydrocooler water. The concentration needed is very low (0.1 per-
cent) and has to be constantly replaced. Also it will precipitate out if the solution
becomes at all acid, as it tends to do with constant aeration and occasional damaged
fruit. For this reason it is advisable to add caustic soda (NaOH, technical grade)
to raise the pH to about 10.5.
DO NOT ADD EXCESS CAUSTIC. Too high a pH prevents the fruit taking up the
necessary amount of Dowicide (about 4 parts per million*) and also causes foaming.
Apart from, the inconvenience, the foar acts as an insulator and can slow up the cool-
ing of the fruit and reduce shine. 1Iild foauing can be controlled with a suitable
A watermeter on the intake to the hydrocooler tank is very helpful. Ihen first
filling the tank its exact capacity in gallons can be read off the water meter.
Thereafter, a record can be kept of make-up water used.
pH Papers The pH can be read almost instantly with these papers. They come
in ready-to-use kits for various ranges. pH 10-12 is needed for Dowicooling. If
these are also to be used for Dow-hex, get the pH 10-14 range.
Dowicide A. (sodium o-phenylphenate, technical grade).
Caustic Soda. (sodium hydroxide). Handle this with care -- remember that it
heats when put in a small quantity of water. It must be kept in a moisture proof
Antifoar,. Foaming can be checked with a little antifoam. A suitable one is Dow-
Corning Antifoam B.
Clipboard and record sheets. For keeping a record of fruit run, chemicals added,
The Food and Drug tolerance (U. S. and Canada) is 10 ppm on a fresh -wqAt basis.
1. Get capacity of tank, either in gallons or, by measurement, as cubic feet.
(I cubic foot = 7 1/2 gallons.)
2. Add Dowicide A to bring concentration up to 0.1%. To get this concentration
add 4 pounds per 500 gallons. If the dry compound is added, shake it in slowly at
the intake to the pump. A better method is to dissolve the Dowicide A in a small
drum or large jar. We use 5-gallon pickle jars in the Experiment Station packing-
house. (Dowicide A goes into a concentrated solution more easily than into a dilute
solution). This concentrate can then be poured into the tank and disperses immediate-
ly. Refill the small container for the next "charge".
3. Raise the pH to 10.5 by adding caustic soda slowly, a little at a time, with
the pump circulating. Too high a pH will render the Dowicide inactive. WTith too low
a pH the Dowicide can be precipitated out by the juice from a few broken oranges.
It is best to add a little often, rather than a lot occasionally. This can also bemad(
up as a concentrate BUT BE CAREFUL, ALWAYS WEAR GLASSES OR GOGGLES W1HEN HANDLING
EITHER OF THESE CONCENTRATED SOLUTIONS. The weak solution in the hydrocooler is
4. If foaming occurs a4d a little antifoam.
Maintaining the Solution
1. pH should be checked at least twice daily when running steadily.
2. For every 500 gallons of make up water, add 4 lbs. Dowicide A. If the hydro-
cooler is in an exposed position (i.e. on the outside platform) and if the tank is
open to the air, the hydrocooler water may pick up almost enough water from the
atmosphere to balance that taken out by the fruit. If this is observed to be happen-
ing, keep track of the amount of fruit being run and add 4 lbs. of Dowicide A for
every 5,000 boxes cooled or per 500 gallons of make up water whichever comes
Testin, the Solution
No rapid test is at present available. However, samples can be brought or
mailed to: "Fruit Handling Section, Citrus Experiment Station, Lake Alfred". A
clean two ounce medicine bottle is ample. These can be obtained from any drug store.
Analyses alone mean little without accurate records. A suggested form is attached
on which the operator of the hydrocooler can keep simple accurate records. A copy
of such records forwarded with a water sample would ensure wore accurate and useful
Obtaining Necessary Equipment and Supplies
All the necessary supplies are obtainable from commercial suppliers, e.g.
Atlantic Chemicals, Inc., Box 3466, Orlando.
"Dowicooling" Page 3
Dowicooling plus other Treatments
Dowicooling can be successfully combined with a Dow-hex application and/or a wax
containing Dowicide A or Dowicide I.
Keeping quality after removal from refrigeration is very much improved by using
two diphenyl 'pads' in each carton. (Qith bagged fruit these go inside the bagmaster
carton, but not inside the bags.) Check with your buyer before using diphenyl. At
present (October 1959) diphenyl is not yet allowed on tangerines.
Packages (bags, cartons, crates) containing Dowicooled fruit must be labeled or
stamped in order to comply with Food and Drug Administration regulations.
Acceptable labels would be:
o-PHENYLPHENOL USED AS A PRESERVATIVE (or "---AS A FUNGICIDE")
SODIUM o-PHENYLPHENATE USED AS A FUNGICIDE (or "---AS A PRESERVATIVE)
OR (when using diphenyl in any form)
DIPHENYL AND o-PIHEYLPHENOL
USED AS PRESERVATIVES
Placards for display in retail bins are no longer necessary.
NOTE: For current information on other decay control methods see "Recommendations
for Control of Decay in Fresh Citrus Fruit" which is issued jointly by the
Florida Citrus Commission (Lakeland), the Florida Citrus Experiment Station
(Lake Alfred) and the U.S.D.A. (Orlando).
_Dowicool iq Record
"lame of packinghouse
Record kept by____
Capacity of tank ..gallo!s.
Date Fruit cooled rVater Dow A Caustic Ru.'ni:,3
-e -4 added added i e
Variety Boxes Tenmp. pH Make up lb, ls
_F. -1s i _bU lbs. (hours)
_,,- 0 ,t
____ _____ __I __ _________' ________
----------------- --- ------------ ----
n)owtcool i Record
T'ame of packinghouse
Record kept by_
Capacity of .ank .allo:s.
- -- --
Dowicooli, tl Record
"Tame of packinghouse
Record kept by_
Capacity of tank gallons.
- --- -------- --- --
Tpowicool i l %. record
Tamne of packinghouse ____ _
Record kept by_ .- -
Capacity of rank allo'8s,
Date Fruit cooled -t1ater Dow3 A Caust.c Ru,mi .T'
-- --_ -- added added ti e
Variety Boxes Teo,.p p- Make up o ls (bhO!rs)
OF. 3 also. lo
'-'-------- ------ T I- -
j------------ --- ----*-~---
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