Citrus Growers Forum

ilyaC · Posted: Mon 18 Jan, 2010 5:16 pm

I know from experience that many frost hardy hybrids have fruits that freeze very rapidly.
What are the most freeze hardy citrus fruits? Is it depends on sugar content?

_________________
Best regards,
Ilya

JoeReal · Posted: Mon 18 Jan, 2010 8:03 pm

ilyaC wrote:

I know from experience that many frost hardy hybrids have fruits that freeze very rapidly.
What are the most freeze hardy citrus fruits? Is it depends on sugar content?

Freeze and frost are two different things, as you have pointed out. Let me just discuss the freezing of the fruits here.

Equally important would be the thickness of the rind (provides insulation), the duration and the temperature. If the subfreezing temperature extends many days, then no amount of insulation or peel will keep the citrus fruits from freezing. But having thicker rind is good, the thicker, the longer the fruits can endure freezing temperature.

Yes, the freezing point depression is dependent on total soluble solids, not only sugar, and their interactions. It can lower the freezing point of water, that is why it is called a depression from pure water freezing point. As to how much, you can read this scientific article:

Relationship Between Freezing Point Depression and Solute Composition of Fruit Juice Systems
C. S. CHEN, T. K. NGUYEN R. J. BRADDOCK
The authors are with the Institute of Food & Agricultural Sciences, Citrus Research & Education Center, Univ. of Florida, 700 Experiment Station Road, Lake Alfred, FL 33850

Florida Agricultural Experiment Station Journal Series No. R-00260.

ilyaC · Posted: Tue 19 Jan, 2010 5:07 pm

JoeReal,

Thank you for interesting background reading.
I agree with you that freeze resistance of fruits is a combination of rind hardiness ( that possibly is related to wood cold resistance) and freezing temperature of juice that depend on its composition.

I know that fruits of poncirus are very resistant to freeze, but for Thomasville citrangequat that is quite hardy the fruits are completely frozen at -6C (~20F).

This year many regions of USA were hit by severe frosts and people rushed to harvest citrus fruits. I wonder if someone have observations of freeze resistance of fruits for different varieties in these extreme conditions?

What are the the most resistant varieties?

_________________
Best regards,
Ilya