Hello there
The color change in your rice probably has to do with the "hardness"
or "alkalinity" of the water you are using for cooking .
In fact, adding alkalinity to the water is an old trick for creating
colored rice. - "... alkaline crystals are dissolved in water, and the
alkaline water added to the rice, mixed well with the sorted rice
grains and left to soak overnight. The alkaline water gives the rice a
pale yellow color, which turns golden yellow after cooking." If you
are in a hard water area, this same process may take place to a lesser
extent simply from the cooking and heated storage process you mention.
( http://www.thingsasian.com/goto_article/article.1587.html ) - the
website is called "Feeding the Dragon."
Also, you may have hit on one reason in your question which is water
loss. - "Color of cooked rice during warm keeping was measured with
the system. The spot analysis was developed as the means of the color
measurement color change of cooked rice. It was found that
discoloration developed in the direction of yellowness and chroma
increased continuously. There was no influence of gas environment
including air, oxygen and nitrogen on the color of cooked rice. On the
other hand discoloration increased in proportion to moisture loss
during warm keeping, indicating moisture loss was the main factor in
determining the color of cooked rice." This ties in with another
piece of information about the iron content of water found later in
the answer.
( http://food.snu.ac.kr/~foodeng/thesis/KyeongMhan.htm ) - While this
page is in English, the website is in Korean and I cannot translate
the name. I would like to know just how "hard" the water was they
used to cook the rice?
It also seems the color change in rice when cooked in hard water is
fairly well known. Here is a method for keeping rice white when
cooking in hard water: - "Cooking Tip: To keep rice white when cooking
in hard water, add 1 teaspoon lemon juice or 1 tablespoon vinegar to
cooking water."
( http://www.pazsaz.com/hints06.html ) - website is "Cooking Hints &
Tips Archive 15 - Pazsaz Entertainment Network"
White rice is not the only food that hard water can turn yellow. - "
Flavones are the white pigments found in potatoes, onions,
cauliflower, and the white parts of celery, cucumbers, and zucchini.
Cook these vegetables for a short time to avoid loss of nutrients,
flavor, and color. Overcooking and hard water turn white vegetables a
dull yellow or gray."
( http://www.ca.uky.edu/agc/pubs/fcs3/fcs3106/fcs3106.htm ) -
"Vegetable Preparation for the Family" by Sandra Bastin, Ph.D., R.D.,
L.D., Extension Food and Nutrition Specialist
More - "Boiled rice is hard and yellow in color-This is due to the
property of high alkalinity in water."
( http://www.twadboard.com/your_doubts.html ) - Tamilnadu Water supply
and Drainage Board website.
The mechanism by which the color change takes place is a combination
of evaporation and hard water. Much of the world's hard water
contains iron and the rice itself can be a source of iron. As water
evaporates, the resulting increased concentrations of iron are yellow
or yellowish brown.
So what it boils down to, is that you are probably in a hard water
area. You can minimize the discoloration in a couple of ways. First
of all, cook the rice in softened or distilled water or add lemon
juice or vinegar as mentioned above. And since you are using a rice
cooker - "Features in keeping rice warm for 24 hours - 1)
Discoloration is prevented by minimizing the temperature adjustment
time after cooking... 2) By realizing low temperature rice keeping at
63ºC, deterioration of steamed rice due to high temperature is
minimized."
( http://www.dreamlg.com/en/cook/useful_features3.shtml ) - a
commercial page for a rice cooker by LG Electronic Inc.
If you are NOT in a hard water area, please let me know and this will
have to be researched from a whole new direction. We'll get the
answer either way.
Search - Google
Key words - discoloration cooked rice, yellowing rice, hard water
cooking, hard water rice cooking, alkalinity +and rice, storing
cooked rice
If I can clarify anything, please let me know.
Cheers
digsalot |
Request for Answer Clarification by
ren29-ga
on
27 Sep 2002 20:13 PDT
Dear digsalot:
Thanks for your anwser,it is substantial in content.
However,what I interesting is the foctor of keep warm cooked rice in
an electric rice cooker.In my experence,the color of rice will change
from white to yellow after keep warm 1-2 days even use soft water.I
wanna know what happen to the rice during the keeping warm time such
as structure change,component change,chemical reaction etc.And the
mechanism of those factors make the color change.
I need paper support by learned journal such as "Journal of food
science","Food chemistry" etc.
Thanks for your answer.
Cheers
Ren29
|
