Hello there
First of all, drying does not improve the quality of fruits or
vegetables. You need to start with the best and most flavorful you
can find.
I will begin with part "B" of your question which asks: "what are the
cut-off points of dehydration (Moisture Reduction) at which such
(flavor) losses occur?" - second bracket mine.
Flavor is not the most important aspect for deciding on a cut off
point. The cessation of microbial growth is - as first and formost
'drying' is a preservation method rather than one of simple
convenience, though both to play their part.
For this, I will be speaking to the Equilibrium Relative Humidity
(ERH) which is a term used to describe the availability of the water
to the chemical environment and microorganisms present in foods.
Fresh foods, such as vegetables and fruit, have an ERH close to 100
percent. An ERH level this high means that the water present in these
foods is available for rapid growth of microorganisms leading to
deterioration and spoilage. By drying foods it is possible to lower
the ERH. As the percent ERH is lowered, the growth of microorganisms
slows or ceases since the water is no longer as available for them.
This occurs at an ERH of 60 percent. Therefore, all foods must be
dried to below 60 percent ERH and kept in a dry environment to be
shelf stable from microbial growth because microorganisms cannot
survive below this ERH level. Even if you had a better flavor
potential above this limit, the food could very well be dangerous for
consumption.
Of course, there are other factors involved. While drying foods to 60
percent ERH prevents most microbial growth, certain chemical reactions
caused by enzymes can still take place which results in spoilage and
deterioration of the product. Fresh produce contains several
different enzymes which cause loss of color, loss of nutrients, and
flavor changes when dried. These enzymes must be inactivated to
prevent such reactions from taking place.
We are getting into part "A" here.
We need to inactivate enzymes in vegetables by the blanching process.
Blanching is the exposure of the vegetables to boiling water or steam
for a brief period of time. Blanched vegetables when dried will have
better color and flavor than unblanched. However, the onion is an
exception as no blanching is required.
As to 'why' a drying onion loses flavor, there are a variety of
reasons.
Some of that flavor loss takes place after the drying process is
completed. Dried onion should be stored in a cool, dry place, away
from exposure to air which would result in moisture pick-up which
causes flavor loss. Heat, even that used in the drying process, also
causes loss. There is evaporation of some volatile flavor oils as
well as moisture during the drying process whether sun drying or any
other method. Since volatile oils evaporate readily at normal
temperatures, the increased heat in the drying process can only speed
this process up. In fact you should close the containers tightly
after each use so that additional volatile oils are not lost. Of
course these flavor oils are not restored during the rehydration
process. Only the water is.
Undoubetedly the flavor loss would be less if the drying dehydration
point were higher but because of safety reasons ( refer back to the
beginning of the answer), even if there is less flavor loss at a
higher cut off point, if I recommended drying to a higher ERH than the
60 posted, I would be recommending that you do something dangerous.
That would be both against our policy and my personal feelings about
the matter. Whether personal feelings should be involved at all is
another matter but for your own safety I will give the final answer to
part "B" as being an ERH of 60.
The following websites were used to compose the answer:
"Drying Food" - http://www.ag.uiuc.edu/~vista/html_pubs/DRYING/dryfood.html
- Website from University of Illinois at Urbana-Champaign
"McCormick Flavor Guide - Onion" -
http://www2.mccormick.com/Flavor_Guide.nsf/0/bd74bbd58008cd45862565d700023790?OpenDocument
- From McCormick Spices
"Drying Onions - Suite 101.com" -
http://www.suite101.com/article.cfm/1068/64592
"Consumer and Family Sciences Consumer and Family Sciences" - PDF
file, Acrobat Reader needed
http://persephone.agcom.purdue.edu/AgCom/ Pubs/CFS/CFS-146-W.pdf - A
website of Purdue University
"Drying Vegetables" -
http://www.ext.colostate.edu/pubs/foodnut/09308.html - A website of
Colorado State University
"Drying Vegetables" -
http://edis.ifas.ufl.edu/scripts/htmlgen.exe?DOCUMENT_HE526 - A
University of florida website
"UACES: Publications: Drying Vegetables" - a PDF file, Acrobat Reader
needed
http://www.uaex.edu/Other_Areas/publications/ HTML/FSHED-56.asp - A
University of Arkansas Website
If I may clarify anything before you rate the answer, please ask.
Cheers
digsalot |
Request for Answer Clarification by
pownergy-ga
on
21 Jul 2003 03:16 PDT
Hello,
We thank you for your prompt response on 17th July 2003.
Your clarifications are highly informative and educative. However they
do not meet with the purpose for which we sought the clarifications
for the reasons stated hereunder.
1. We are a manufacturer for Fried Onion for the International Market
and now looking for the prospect of marketing the Fresh Onion after
dressing, cutting (slicing)and packing in a commercial packs
(transparent plastic cases), by displaying / storing in ambient
temperature of about 25 Deg Centigrade. The transparent plastic cases
are made of high barrier properties which prevent oxygen permeability.
We like to maintain the percentage of ERH at a level, even if it is
higher than 60%, which will retain the original / natural flavour and
taste (pungency). Obviously, the intended commercial pack will carry
the oxygen while sealing the pack and also the moisture in the packed
onion will continue to release oxygen. In order to overcome this, we
intend identifying an ideal Oxygen Absorber, which will be stuck
inside the pack (We are already in touch with a few manufacturers of
Oxygen Absorber, seeking their guidance in this regard). This Oxygen
Absorber is expected of absorbing the oxygen continuosly, so that the
packed Onion will continue to retain the flavour, taste and colour,
over a period say 3 / 6 months, even by storing / displaying at an
ambient temperature of about 25 Deg Centigrade. It is only with this
object, we raised the query of "Cut-Off Points of Dehydration
(Moisture Reduction)"
2. In our overall objective, drying / dehydrating is only incidental;
since our main objective is only to preserve the flavour and taste.
3. You mentioned about evaporation of some volatile flavour oils. (And
perhaps volatile oils relate to taste also ?) Are there findings
available on this evaporation of Oils at particular temperatures / ERH
levels ?
4. We understand from the website references given by you that
"Essential Onion Flavours" are being marketed by McCormick Spices and
Qualy-Gomei (Mexico). We presume they are the extracts from Onions. If
so the evaporating point of flavour oil in the Fresh Onion should have
been identified.
Based on our above narrations / explanations, we request you to guide
us.
Regards.
|
Clarification of Answer by
digsalot-ga
on
21 Jul 2003 04:00 PDT
You have just made the question much more interesting. LOL, from the
initial question I was picturing a home hobbiest looking for a more
practical way to dry produce. That's why I was such a stickler for
the ERH of 60. I didn't want somebody getting sick because of an
answer they got here.
I will tackle this when I get back this afternoon.
Cheers
digs
|
Clarification of Answer by
digsalot-ga
on
21 Jul 2003 10:54 PDT
Now then, if I could get some more information from you, it will make
things easier to track down and provide an answer that you can use.
1 - It sounds as though you will be using a cold packing process
rather than heat. Do I understand that right? - - - The reason I need
to know is that not all volatile flavor oils evaporate at the same
point. Dehydration in any amount changes the flavor due to the loss
of the low 'boiling point fraction' of the essential oils. Another
fraction of the oils has a higher boiling point, etc.
2 - If you are using a cold packing method, there may be a chance you
can avoid flavor loss. You mention that due to the packaging you can
run at a higher ERH level than 60. This may very well change the
whole complexion of the question or even the need for an answer
dealing with dehydration, but have you considered packing at full ERH?
- No loss of moisture at all or a minimal loss at worst?
3 - Are you trying to maintain an "organic" image or is the use of
preservative acceptable if it helps maintain flavor and shelf life
within the storage parameters you have given?
4 - You mention evaporation points for onion oils extracted by
McCormick Spices and Qualy-Gomei. I will try to find them but it may
well be that since we are dealing with corporate information from
these companies, such information provided by them may be 'privilaged'
and available by subscription only.
The answers to the first three above will tell me which direction you
need for me to go.
digs
|
Clarification of Answer by
digsalot-ga
on
21 Jul 2003 11:03 PDT
There is one other aspect I should throw in here while you are
thinking about my above clarification request. It is an aspect rather
unrelated to the original dehydration question, but you did say you
were going to 'slice' the onions.
That alone can cause a flavor loss. Certain vegetables, mainly members
of the Allium family (like onion and garlic), have a characteristic
flavor and odor which is caused by an enzymatic reaction with
naturally occurring sulfur compounds. Cutting the cells releases the
enzyme allinase which promotes the development of these flavor
compounds. Once the onion is cut, there is an additional loss of
volatile flavor components. Not all is oil based, some is water based
in this instance.
|
Clarification of Answer by
digsalot-ga
on
23 Jul 2003 12:22 PDT
While waiting for the answer to my clarification request, I've gone
ahead and begun research on the the flavor extraction process as you
requested.
What I am finding is that onion flavor chemistry and things which
influence flavor intensity fill books. Thanks to the fact that you
have demonstrated some patience while I put together this answer means
that I should have the time to try and "extract" some of this
information and assemble it in a usable form.
One major source which I will be using heavily is:
"Onion flavor chemistry and factors influencing flavor intensity. In
`Spices: Flavor Chemistry and Antioxidant Properties' Risch S.J., Ho
C.-T. (Eds) ACS Symposium Series 660, American Chemical Society,
1997."
I am simply waiting for permission to quote fairly large blocks of
text from the American Chemical Society.
|
Request for Answer Clarification by
pownergy-ga
on
24 Jul 2003 01:08 PDT
Hello Digs,
I greatly admire your perseverance in having made 4 dispatches in 3
days. As I have been away on tour, could not respond to you earlier.
My responses in seriatim are as follows :-
1. Regarding 1st dispatch on 21st July: I am glad I could picturise
myself properly.
2. Regarding 2nd dispatch on 21st July: The following are my answers
to the four points raised.
a) Till now, I am conceiving of only heat process to bring down the
moisture. I have also noted that essential oils evaporate at different
boiling points.
b) I have noted that there me be a chance for avoidance of flavour
loss in case of “cold packing method”. Is there possibility of
reducing the moisture (ERH) level by cold packing process ? Kindly
guide me.
I have not considered, till now, packing at full ERH. As you have
rightly pointed out, if oxygen absorbency technology can take care of
this, I would appreciate. In this regard I will seek the guidance of
manufacturers of oxygen absorbers with whom I have been in touch with.
In the meantime, if you find any such possibilities, kindly advise me.
c) Till now, I am trying to maintain an “organic image”, as it will
have better market acceptability. I greatly appreciate your indication
of using “preservative” for maintaining flavour and shelf-life by
displaying / storing in ambient temperature of about 25 Deg
Centigrade. Do you have in mind any such preservative for this purpose
? Perhaps it may be prudent to go by such acceptable preservative, if
it can objectively meet with my requirement of maintaining flavour,
taste and shelf life.
d) In consideration of the practical difficulties in getting the
privileged informations from corporate bodies, we may put that issue
on hold for the time being.
3. Regarding 3rd dispatch on 21st July: My preference for “Sliced
Onion” is due to the following facts.
a) It is already dressed and cut in a desired form and ready for use
in the Kitchen, and
b) It helps the consumer not to shed tears while cutting due to
Sulphur compounds in the Onion.
I have noted the point that loss of certain amount of flavour,
consequent on cutting. Perhaps this is an inevitable compromise I
should have. Will cutting the Onion affect the taste (pungency),
similar to flavour ?
4. Regarding 4th dispatch on 23rd July : I am happy to know of your
attempt to “extract” informations from the American Chemical Society,
in respect of Onion Flavour Chemistry. I wish you succeed at the
earliest.
Regards,
Siva
pownergy-ga
|
Clarification of Answer by
digsalot-ga
on
24 Jul 2003 01:21 PDT
Thank you for sending the additional information and I should be back
to you in a day or so.
digs
|
Clarification of Answer by
digsalot-ga
on
24 Jul 2003 13:26 PDT
Well, I will start with a figure which surprised me when I read it.
It takes over 12,000 pounds of onions to yield a little over eight
ounces of onion oils.
Now that has little to do with the answer. I just thought it was an
interesting statistic which demonstrated the lengths spice and
flavoring companies will go to provide a product.
However, for what you want to do, the real flavor saving cut off point
has less to do with the ERH than it does with temperature.
"In the fruit and vegetable dehydration industry, it is well
established that higher processing temperatures can reduce quality in
the critical areas of nutrition, color, aroma, taste, texture and
rehydration rates. The relationship between tangible product quality
and process air temperature is well established for premium dried
fruits and vegetables.
"Onion dehydrators learned long ago that undesirable pinking occurred
when product temperatures became elevated, resulting in the use of
large, multistaged dryers to avoid temperature rise in onions. Extract
studies on products containing volatile aromatic oils confirm that 50%
declines in essential oils occur when the product is processed at
higher temperatures. " - From Business News Publishing Co.
http://www.process-heating.com/CDA/ArticleInformation/features/BNP__Features__Item/0,3156,12842,00.html
Since you are not drying onion at home as I originally thought, the
article quoted above contains information about commercial drying
equipment and how temperatures are controled in such equipment
including the following: - - "During initial drying, evaporation of
surface moisture provides sufficient product cooling to offset any
convective heating of the product by the process air. This cooling
effect remains constant until the rate of surface evaporation exceeds
the ability of internal moisture to migrate to the surface, at which
time the product begins to heat up, accelerating the internal rate of
moisture transfer. This point, known as the critical moisture point."
I cannot tell you exactly what this point is because it varies with
the type of dryer, air fans, air flow rates and other factors that
would be product specific to the type and brand of dryer used. I
think this is the real answer to part "B" of your question even though
it deals with temperatures rather than purely with ERH.
I also have a feeling you are attempting to create a product that has
never been done before. So I thought I would throw this in now and
get it out of the way. Even though you are using plastic containers,
in essence you are "canning" fresh onions. The following exchange is
from a cooking website:
"Q. How come the only directions I can find on canning onions are for
pickled onions?
A. Because that's the only way to can onions and have an edible
product!" - http://www.homenfamily.com/canning/garliconionsfaqtips.html
Now we have to see if there is a way around that. I know that French
fried onions can be canned. I've eaten enough of them broken up in
salads and as snacks. But we are talking about an essential 'raw'
product in your case.
In spite of the above, there is a recipe for canning onions but it
involves small onions and cooking them. I found many ways of cold
packing vegetables but it seems the onion does not lend itself to that
process.
When it comes to the preservative I was asking about, I was thinking
of the addition of ascorbic acid to prevent some discoloration, though
it will have little effect on flavor. While ascorbic must be listed
as an artificial preservative, it is in reality plain old vitamin C.
The preservative mix is the equivilant of one teaspoon of ascorbic
acid powder per gallon of water. Premixed solutions are also
available for large scale use.
Another reason for this preservative is that onions are a low acid
vegetable and if they are going to be processed and packaged, they
need to be acidified to assure sterilization and to prevent spoilage.
A pH of 4.5 is desirable. The acid solution may be used as a dip, or
may be added direct to the package. - From the US Department of
Agriculture
I hate to say it, but even the US Department of Agriculture database
on food preservation has no information about processing and packaging
onions in the manner you are suggesting. You will find access to the
entire database here - http://foodsafety.cas.psu.edu/presqueryform.cfm
I have also checked to see if vacuum packing might be a way to go for
you. What the results are is a shelf life of at least 24 days at
retail and 35 for foodservice. Even then, we are not talking about a
"raw" product. Vacuum packing is a patented process that results in a
fat-free, preservative-free, 80 percent-cooked product. The process
doesn't vary, regardless of the commodity:
http://tinyurl.com/hwds - Redi Foods - Please note that this is a link
to a cached page. The original page is no longer on line so you may
want to make a copy of it.
The partial cooking process is necessary even in vacuum packing as the
vacuum packing process itself does not stop bacterial growth and a
sterilizing step is necessary. Vacuum packing would of course
eliminate the need for an oxygen absorbant.
While we are on the subject of sterilization, even though partial
drying, an oxygen absorbant and ascorbic acid will slow some of the
bacterial growth process, anaerobic bacteria could still thrive in the
type of package you have described. That is not to say "they will,"
but the possibility is there and it would take only one customer out
of a million getting a "bad" product to create some problems.
Now we can get into some of the reasons onions lose their flavor. It
can be quite complicated and it begins with the vegetable itself.
"Flavor is unequally distributed within the onion plant and is
dependent on onion ontogeny. Within the bulb, there is a flavor
gradient. The highest concentration of precursors occurs in the
interior base of the bulb, while thelowest concentration of precursors
are in the top outside scales. As the plant and bulb grows, flavor
first increases in intensity, but then decreases as the as the
bulbswells to maximum size and matures . Onion flavor and intensity
also changeduring storage. Some cultivars increase in flavor intensity
during storage while others decrease. The ratio of the different
precursors can also change during storage. In one onion cultivar, the
1-propenyl thiosulfinates significantly increased in concentration
during six months of storage while the methyl methane thiosulfinates
completely disappeared (per corn. Norman Schmidt, Dept. of Chem.,
Georgia Southern University).Environmental Factors and Flavor
Intensity." - This is a quote from the American Chemical Society
article I mentioned.
In as much as there is a lot of information presented, I will link you
directly to the article rather than try to quote the whole thing
(which would be against our rules considering I have received no
permissions from them even after asking.)
http://www.uga.edu/onion/pdf%20files/Onion%20flavor%20chemistry%20opt.pdf
- - This is a PDF file. Acrobat Reader is needed.
Which brings us back to your original question: "(A) What are the
causes for such losses ? and (B) what are the cut-off
points of dehydration (Moisture Reduction) at which such losses
occur?"
The first part "What are the causes for such losses," can be a complex
answer but the main point as far as your project is concerned would be
heat and the resultant loss of flavor oils. The answer to the second
part is related to the first in that heat is more important than water
loss to the overall flavor and the "cut off" point would be determined
by the type of drying equipment used.
I also realize I have gone all over the place with this answer, but I
was trying to anticipate some additional questions the answer to your
main question would lead to. I also hope this answer does not scare
you away from your project. I would love to find such a product in
the market.
There is also one other solution. When you have the production and
packaging process fully developed, simply use an onion cultivar which
has a stronger pungency than you want to present in the final product.
That way any flavor loss will being the product "down to target"
rather than bringing it in below target.
If even the USDA has no information about the onion processing method
you propose, it is highly likely there is little or no information
about the process available or such a process has yet to be developed.
If you can do that, you will have an extremely valuable piece of
intellectual property.
I wish you the best and hope to see such a product on the market soon.
If I may provide further clarification, please ask.
digs
|
Request for Answer Clarification by
pownergy-ga
on
29 Jul 2003 19:52 PDT
Thanks for your detailed clarification on 24th July.
I am in consultation with my technical staff / consultant.
Hope to revert back in a week's time. In the meantime, if you have any
additional informations, kindly dispatch.
Regards.
|
Clarification of Answer by
digsalot-ga
on
29 Jul 2003 21:12 PDT
I'm still doing some research on this. As I say, it is a product I
would like to see on the market. Good luck with your technicakl
staff.
digs
|
Request for Answer Clarification by
pownergy-ga
on
13 Aug 2003 20:35 PDT
Dear Digs,
I am thankful to you for your continued guidance on the subject. In
fact my technical staff are working on the product and hopeful of
positive outcome. I will keep you informed.
In the meantime, I seek your continued guidance, since you stated in
your message dated 29th July 2003 stating that “ I am still doing some
research on this”.
Regards.
|
Clarification of Answer by
digsalot-ga
on
13 Aug 2003 22:03 PDT
Hello again.
When I was looking, I found mostly a rehash of what has already been
covered. I was hoping that since you said you would be in touch after
your meetings, there might be something you have learned which could
point in some new directions.
Everything points to one solution. You are going to lose some flavor
to the drying process (regardless of how only 'partial' it may be, and
you will lose some flavor to whatever the sterilization process is you
will use.
And that is the solution that was almost a 'throw away' in the answer.
Process an onion cultivar which has a flavor level higher than what
you want your final product to be. It is far easier to tame an onion
that is 'too strong' than it is to add 'zip' to one which is already
lacking.
In fact, such onions may be easier for your business to process as the
more pungent varieties are also the easiest to keep. Their already
low water content inhibits mold and spoilage during storage.
And you would want to store them. Unlike other produce which is
usually processed fresh on arrival at the plant, the pungent onions
develop even more pungency with storage.
Your arrival shed and grading room may be set up in such a way that
you are always receiving onions a month in advance of the processing
date.
As onions come in, they go past the graders. Then instead of being
sent along the line to the processing room, run them into storage
boxes and put away for a month. At the end of the month they continue
on their way. You will then always have a rotation of 'aged' high
potency onions continually feeding into your processing lines.
Of these kinds of onions which include Bermuda, Red and White
varieties, the best I can think of for your situation would be the
'Yellow' onions. They are the best keepers and they are already the
most pungent.
For your bottom line, they are also the least expensive.
http://www.digsmagazine.com/nourish/nourish_cluelesscooks_onions-color.htm
digs
|
