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- wineguruchgo - 01-21-2004
Hello winefriends,
It is not very often that I find myself asking for help, yet here I am.
As some of you know I'm starting to study for the Master program of wine and with this study comes questions. I'm hoping someone will have an answer.
I've read that many time in cool weather climates they will spray water on young vines to actually encapsulate them in ice to protect them from frost.
Now I understand (igloo theory) that it actually can be warmer inside - yet I'm having trouble wrapping my brain around the fact that the vines being shrouded in ice won't do any damage, yet frost will.
Any thoughts?
Thanks!
BTW - Where would you like me to post questions such as this? Something tells me I might come across more in my studies.
- marleyspud - 01-21-2004
Interesting query! I would be intersted in the answer also. MS
- Skeeter - 01-21-2004
I did a little Googling, and found this in a research paper from California Agricultural Tech.
"Use of sprinklers can protect vines when temperatures fall to -3.9°C (25°F), if conditions are ideal. Water from the sprinklers supplies heat to the vine-water- atmosphere system. The heat is released as water cools to 0°C (32°F) and then freezes to ice. The most important factor in this situation is the heat of fusion (released as water freezes to ice). A gallon of water releases 300kcal (1200 BTU) of heat as it freezes."
So they are in fact heating the grapes with ice.
Weird, huh? [img]http://38.118.142.245/ubb2/smile.gif[/img]
Why this is different from frost, I'm not sure.
- tandkvd - 01-21-2004
I don't know how accurate this therory is but here is my thought.
Water freezes at 32 deg. F. But to have frost to develop on the grapes the actual temperature of the grapes would have to drop below the dew point of the air, which in a low humidity situation would be well below 32 deg. F. Thus the grapes would be getting to a lower temperature before the ice forms on them.
But with the water allready on them by use of sprinklers the protection from the ice layre starts at a higher temperature.
IMHO of course.
- Innkeeper - 01-21-2004
Unless I've got the facts wrong (again) I think that orange growers in Florida do the same thing.
- wineguruchgo - 01-21-2004
Innkeeper,
Now that you mention it I think I remember something about the orange growers doing it as well.
Tankvd,
Your theory doesn't sound that far fetched. I've got to do some more digging. I'll let you know.
- Tastevin - 01-21-2004
Very well put tandkvd.
There is an amusing piece of folk lore relating to this subject; it goes something like this.
Many moons ago in Chablis, a young peasant and the daughter of a vineyard owner fell in love. One day the young lady's father and mother, both being a reasonable couple, invited the beau to dinner and to stay the night (in his own room of course!) at their chateau. During the night the young man woke wanting to relieve his bladder rather badly. Not remembering where in the vast chateau was the toilet, he had no alternative but to relieve himself through his bedroom window.
Unfortunately for his host there was a frost during the early hours of the morning, as a result all his vines were ruined. All that is, except one which he noticed had a covering of yellow ice! That's why ever since then, whenever frost threatens in Chablis, all the young men are expected to have full bladders every night ready to pee over the vines.
No, not really.
Ever since then, whenever frost threatens in Chablis the vines are usually sprayed with water (I say 'usually', because some put lighted braziers between the rows of vines).
So goes the story about the discovery of the benefit of spraying vines with water. Believe it or not - your choice! T
- wineguruchgo - 01-21-2004
Cute (?) story.
Here is what I have found on the subject and your answers were on the mark!
Frost damage, or ‘burn,’ is caused when freezing temperatures cause vine cells to burst and die. While the vine’s secondary buds will be activated if the growth from the primary buds is killed, those secondary buds contain only about half of the crop potential present in the primary buds. If a vineyard is capable of producing four tons per acre and frost destroys the growth from all of its primary buds, the yield would be reduced to about two tons per acre. Since tertiary (third) buds have about half the fruiting potential of secondary buds, a later frost event destroying the secondary buds’ growth would reduce the yield to just one ton per acre.
So how do you keep vines from freezing? While vineyard managers historically have employed several techniques, the most effective uses water. Water-based frost protection systems work by creating wet ice around a vine’s green leaves, shoots and buds. Water freezes at 32°F; even if the surrounding air temperature is lower, ice with a wet surface can’t get below 32°F. But young vine growth can survive to a hair below 31°F. A long as liquid water is actively freezing around it, the vines never experience temperatures low enough to cause damage. The key word there is liquid—if the surface of the ice isn’t wet, the temperature of the ice can drop to well below 32°F.
If you had asked me yesterday which would do more damage to a vine I would have put ice over frost.
Amazing!
- tandkvd - 01-21-2004
I like that story Tastevin.
I have done a little research on this subject now that I'm home from work and have a little more time.
Check out this site: http://www.rainbird.com/pdf/ag/frost.pdf
Btu = the amount of heat required to raise 1 lb. of water 1 deg. F.
The latent heat of fusion.
It takes 144 btu's to melt 1 lb. of 32 deg. ice.
A ton of ice melting in 24 hours will absorb heat at the rate of 12,000 Btu per hour. As seen in this formula.
144 = btu to melt 1 lb. of ice
2000 = 1 ton of ice
24 = hours
144 x 2000 divided by 24 = 12,000.
This is where you get the term ton of air conditioning.
The latent heat of vaporization.
It takes 970 Btu's to boil 1 lb. of 212 deg. F water to 1 lb. of steam.
[This message has been edited by tandkvd (edited 01-21-2004).]
[This message has been edited by tandkvd (edited 01-21-2004).]
[This message has been edited by tandkvd (edited 01-21-2004).]
- yabloka - 01-31-2004
Doesn't heat of fusion take place a 0 degrees celsius when ice converts to water? I don't think it would be used in the reverse, but I could be wrong.
- sedhed - 01-31-2004
IK is right about oranges.
- tandkvd - 01-31-2004
The way I understand the heat of fusion is it goes both ways. You can have 1lb. of ice at 32 deg F and you can have 1lb. of water at 32 deg. F. Either way you are going to have to remove 144 btu's to freeze the water or add 144 btu's to melt the ice.
But once the heat of fusion is accomplished, say in the instance of melting 1lb. of ice to 1lb. of water, then it takes only 1 btu of heat added to raise the temp. of the water 1 deg. F.
So, if you have 1lb. of ice at 32 deg. F. And you add 288 btu's of heat, you will have 144 deg. water.
- Innkeeper - 01-31-2004
Does this have anything to do with the fact that ice and water in an ice bucket chills wine faster than just ice?
- tandkvd - 01-31-2004
It should IK, because as long as there is a ice and water mixture it will be 32 deg. F. And the wine bottle will be in contact at all points to help with the transfer of heat from the wine to the ice/water mixture. If you only have ice in a bucket there are air gaps between the ice and the wine bottle, that is, not all points of the wine bottle are in contact with the ice. And air is an insulator which would inhibit the transfer of heat to the ice.