I can taste the difference in water heated in a microwave versus that heated
on the stove. No problem. I am mostly aware of the difference when I brew
a cup of tea.
Except for doing tests, I absolutely will not drink tea from water heated in
a cup in a microwave oven. It is clearly inferior to tea made with water
heated in a tea kettle on a stove. I don't need any double-blind tests to
tell me this; it's obvious. I have observed it many times both by taste and
by sight. Yes, by sight. Our water in Bluffton has a fairly high mineral
content. If tea is made with microwave-heated water the scum on top is
worse than if the tea is made with stove-heated water.
-- ions -- I assume, as others have stated, the difference is mostly metal
ions from the tea kettle. My preferred tea kettle has stainless steel sides
and a copper bottom. I suspect the copper is the key.
I have used regular hard tap water (high in calcium and magnesium), softened
water (high in sodium), distilled water, reverse-osmosis water (90% of
hardness removed). I have heated water in stainless steel, aluminum,
copper, ceramic, etc.
Remember, when we make tea we are doing an extraction. We are extracting
compounds (mostly organic compounds) from a natural substance (tea leaves).
We know that the presence of other things in the solvent (like metal ions)
can greatly affect the efficiency of extraction of various compounds. We
know drinks like tea and coffee have a balance of a large number (over 100)
chemicals. Changes in this balance make changes in taste... this should be
obvious.
In my opinion, the best tea comes from RO water brought to a boil on a stove
top using a kettle that has some copper in it. If the water hardness is too
high, the calcium/magnesium apparently interferes with the balance of
compounds extracted from the leaves. But distilled water is also bad
because it seems to extract too many bitter compounds from the leaves.
Water with a bit of +2 ions like Ca and Mg (and maybe Cu) seems to give a
balance I like. A typical RO unit used by homeowners will remove about 90%
of the Ca and Mg. The resulting small amount of Ca and Mg seems just about
right for good tasting water and tea and coffee. However, some people who
like a fairly astringent tea may prefer the taste of tea made with distilled
water.
-- oxygen - Some say there should be some oxygen remaining in water used for
tea. Therefore, do not boil it too long. This is less obvious to me. Tea
does have antioxidants in it. Leaving some dissolved oxygen in tea might
have some effect on the antioxidants, but I am not sure of the chemistry.
Dissolved oxygen (molecular) might react with some antioxidants. But some
things classified as biological antioxidants are not working on molecular
oxygen. Also, the antioxidant potential of tea has been promoted as good
for us. In that case maybe we would want the oxygen boiled away to make
sure the antioxidants are preserved. I just don't know enough about this.
-- temperature - The extraction process clearly depends on temperature. The
taste of brewed tea and brewed coffee clearly depends on temperature. Water
heated in a microwave can superheat. When the tea bag/ball is added there
can be boiling. This is a really easy way to make a bad cup of tea. The
recommended method for brewing tea is to heat water on a stove until it
comes to a rolling boil. Do not boil any longer than that. Remove the
kettle from the stove and hold it for about ten seconds. The goal is to get
the temperature to drop just a couple degrees. Then pour this over the tea
bag/ball which is already in the cup.
-- summary-Although this discussion has some characteristics of "witchcraft"
or "folk-legend," I do not think this is totally true. There is no doubt
that the human tongue is sensitive to slight changes in the balance of ions
and flavors. There is no doubt that ions present in a solvent affect the
extraction process. There is no doubt that temperature greatly affects the
extraction process. The only aspect I am not certain about is the dissolved
oxygen.
* * * About this thread * * *
An interesting thing about this thread is the different directions people
have taken. Some apparently viewed the question as dumb and responded
somewhat sternly or responded tongue-in-cheek. Others took it seriously and
looked for physical explanations. Others took it seriously and looked for
chemical explanations.
I take the question seriously and think the difference is mostly chemical,
but could be partly physical-chemical caused by the possibility of
superheating in the microwave. The actual personal experience will be
enhanced/reduced by the quality of water used, the type of utensil used to
contain the water during heating, the length of time the water is heated,
and how the water is used (straight, tea, coffee, etc.)
BTW - are you aware that it is pretty well established that if you make
whipped cream or if you whip egg whites in a copper bowl you will get much
better results than if you whip these things in glass or stainless-steel
bowls? Tests performed seem to indicate trace amounts of copper ions are
the key.
BTW - are you aware that biochemists doing work in enzymology typically have
to be very careful to avoid copper utensils because even trace copper ions
can deactivate many enzymes.
Michael D. Edmiston, Ph.D. Phone/voice-mail: 419-358-3270
Professor of Chemistry & Physics FAX: 419-358-3323
Chairman, Science Department E-Mail edmiston@bluffton.edu
Bluffton College
280 West College Avenue
Bluffton, OH 45817