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Varieties of Alkaline solution which are used in foreign producing countries specially
California, Australia, and Greece, can be divided into two categories. One is simple
solutions and the other is Alkaline oil solutions. In addition to these solutions, in some of
the countries and for special varieties of raisins, Anidirid Sulphoro is used as well.
Alkaline solution used in California state includes simple soda solution and oil
soda solution.

Simple soda solution_ This solution contains %2 to %3 of caustic soda and is usually in
nitrifying Thompson seedless grapes. The temperature of this solution when using should
be between 93 and 100 degrees centigrade ie in process of boiling, they dip the grape
cluster in this solution for only 2 or 3 seconds, and after taking it out of the solution,
they will wash the grape cluster with cold fresh water, and they will dry it in the

If the time of remaining the grape in the solution lasts more than 3 seconds, the grape
will be spoiled. So nitrifying the grape with this solution needs much attention and
caution, and so some of the garden owners use Natrium neutral carbonate(CO3Na2) or
Donatrium bicarbonates (CO3HNa) which is weaker than Donatrium Carbonate to weaken
the solution. After placing the grapes in front of the sunlight for 3 days, they will ransack
them and then they will gather them. The produced raisin of this method has a shiny
reddish_brown colour.

Oil Alkaline solution_ They use two kinds of oil solutions in California. First kind with
relatively low temperature(37.7°C equal to 100°F) and the second type with high
temperature.(76.6°C equal to 170°F) The component of these two solutions are different
from each other as well. In the first kind solution, used Alkaline substances include 30lbs
(13.59 kgs) of Donatrium Bicarbonate and 1lb (0.453kg) of caustic soda in 3.78 liters of
water and a little olive oil so that a thin sheet of oil will cover the surface of the
The time of grape remaining in this solution differ from 30 seconds to 3 minutes. The
colour of the produced raisins with these solutions is relatively dark brown.
Commercially, in California, none of these two solutions are used. Only upto 1920 that
the production amount of raisins was not much, they used these solutions. Nowadays,
the main part of raisin product in America is dried and provided directly or naturally ie
without Alkaline solution and with sun heat, but to provide light coloured raisins
(Golden_bleached and Sulphur bleach), they use Alkaline solution and Sulphur soot. The
production method of golden raisins or green raisins is as after cleaning the grape
clusters, they will dip them in Alkaline solution of the first kind for 2 or 3 seconds, then
they will wash them immediately with cold water, and before that the grape skin is
dried, ie instantly after washing the clusters, they will put them on wooden trays and
then they will take them to Sulphur soot room.
The time needed to fumigate the grapes is 2 to 4 hours and about 1 to 2 kgs of Sulphur is
used to fumigate a tone of grapes. In this duration of 2 to 4 hours, the grape should
appear in a colour of light yellow.
After fumigating the grapes, the carry the clusters to the drying machine that its
temperature is 140°F to 160°F(60° to 71°c) to be dried. After finishing this work ie
grapes being dried, the colour of the produced raisins should be Lemon yellow. Another
preparation method of yellow or green raisins which are famous as Sulphur bleach is as
after they have nitrified and fumigated the grapes, they will put them on a wooden tray
like Golden raisins for a period of 3 hours in front of the sunlight, and if the weather is
not favourable, this may last for 24 hour.
After 3 to 24 hours they will ransack the grapes and after another 24 hours, they will put
the wooden trays on each other, and bunch it in a sunny location and to protect the last
wooden tray grape from the direct sunlight, they will put an empty tray on the last floor,
and for this purpose they gather the grape clusters which are at the outer side of the
wooden trays and are exposed to the direct sunlight in the middle of the wooden trays
that is the place of shade.
Approximately 10 days after bunching the wooden trays, each of them is turned down in
another wooden trays that was previously explained, and then they will place them in
the sun in the first method on one another. Drying the grapes with this method will last
for several weeks. To uniform the moisture amount of the raisin singles (generally or by
any other method that the raisins have been produced.), they will place them in a big
box which any of them has a capacity of 50 to 60 kg of raisins, put these boxes in the
open air in a sunny place, and then place them for a relatively long duration in this
The colour of the produced raisins with this method should be light yellow, and if at the
beginning, the grapes remain under the direct sunshine more then needed, they will
have an unfavourable dark colour which leads to an undesirable, low value raisin