You've gotten some helpful replies already.  I have found the following 
reference to be helpful in understanding some of the physics behind 
damage incurred during the crystal cooling process and a general 
strategy to help avoid it.  It expands upon what's already been said - 
that larger crystals are more prone to distress during cooling.  This 
and other papers from the same group contain useful information and advice.

A General Method for Hyperquenching Protein Crystals
Matthew Warkentin and Robert E. Thorne
Struct Funct Genomics. 2007 December ; 8(4): 141–144. 
doi:10.1007/s10969-007-9029-0.

Best,
-Andy


On 4/15/2010 4:48 AM, Mark J. van Raaij wrote:
> and don't forget to check diffraction without freezing.
> Mark
>
> On 15 April 2010 10:37, Anastassis Perrakis <[log in to unmask]
> <mailto:[log in to unmask]>> wrote:
>
>     Hi -
>
>     My two cents:
>
>     First, you say:
>
>>>         I assume the bigger crystal might have lot of solvent which
>>>         prevent for high resolution. If it is true what could be the
>>>         best way to dehydrate crystal without affecting crystal quality?
>>
>
>     I think this assumption is confusing. If the crystals were grown in
>     the same drop/condition, they have identical percentage solvent
>     content. Thus, you do not want to look at dehydration, the
>     'percentage solvent content' is fine. What you want to look at is
>     the mechanics of vitrification. Big crystals, are simply hard to
>     freeze: because of their volume they cannot be vitrified as rapidly
>     and uniformly as smaller crystals. I will not be surprised if there
>     are papers that quantify that, but what I am saying here is only
>     from experience and adding a 'logical' explanation to that experience.
>
>     Thus, I would simply stay with the smaller crystals (I have a
>     feeling that you 'small' crystals are 'big' for many other people)
>     and be happy they diffract to 2.5 A (is that SR or RA?)
>
>     A.
>
>
>     On Apr 15, 2010, at 3:16, syed ibrahim wrote:
>
>>
>>     Dear Jurgen and Ho Leung
>>
>>     To add few more point regarding my question:
>>
>>     1. Crystal was first  frozen in LN2 and then transfered to cryo
>>     stream (in presence of LN2 in vial)
>>     2. Anealing did not help (both short time and long time) -
>>     perhaps the crystal dies.
>>     3.  Spots are clear to available resolution (is:  6-7A). In the
>>     high resolution region there is no spot but looks like smear in
>>     the whole area.
>>     4. The crystal was approximately 1.0mm length and 0.4mm dia. I
>>     mounted on 0.5mm loop. So the liquid around the crystal was very
>>     less. I deliberately avoided more solvent in the loop to help
>>     diffraction.
>>
>>     Thanks
>>
>>     Syed
>>
>>
>>
>>     --- On *Thu, 4/15/10, Jürgen Bosch /<[log in to unmask]
>>     <mailto:[log in to unmask]>>/* wrote:
>>
>>
>>         From: Jürgen Bosch <[log in to unmask] <mailto:[log in to unmask]>>
>>         Subject: Re: [ccp4bb] Cryo Vs crystal size
>>         To: [log in to unmask] <mailto:[log in to unmask]>
>>         Date: Thursday, April 15, 2010, 3:46 AM
>>
>>         There are a couple of additional factors not taken into
>>         account here.
>>
>>         1. LN2 versus frozen in strem or propane etc
>>         2. did you try to flash anneal the larger crystal
>>         3. smeary diffraction from the big crystal or not ?
>>         4. how much residual solvent was around your crystal when
>>         freezing ?
>>
>>         In general smaller crystals are anyhow better in my hands.
>>
>>         Jürgen
>>
>>         On Apr 14, 2010, at 5:36 PM, syed ibrahim wrote:
>>
>>>         Hi All
>>>
>>>         I had two crystals grown in same well, one is small and other
>>>         is 10 times bigger. I treated both crystal in same cryo and
>>>         same time. The smaller one diffracted to 2.5A and the bigger
>>>         one to 6-7A. I was expecting the bigger one to diffract high
>>>         resolution.
>>>
>>>         I assume the bigger crystal might have lot of solvent which
>>>         prevent for high resolution. If it is true what could be the
>>>         best way to dehydrate crystal without affecting crystal quality?
>>>
>>>         Thank you
>>>
>>>         Syed
>>>
>>>         PS: Taken care of less solvent to be present in the loop
>>>
>>>
>>>
>>
>>         -
>>         Jürgen Bosch
>>         Johns Hopkins Bloomberg School of Public Health
>>         Department of Biochemistry & Molecular Biology
>>         Johns Hopkins Malaria Research Institute
>>         615 North Wolfe Street, W8708
>>         Baltimore, MD 21205
>>         Phone: +1-410-614-4742
>>         Lab:      +1-410-614-4894
>>         Fax:      +1-410-955-3655
>>         http://web.mac.com/bosch_lab/ <http://web.me.com/bosch_lab/>
>>
>>
>
>     *P** **please don't print this e-mail unless you really need to*
>     Anastassis (Tassos) Perrakis, Principal Investigator / Staff Member
>     Department of Biochemistry (B8)
>     Netherlands Cancer Institute,
>     Dept. B8, 1066 CX Amsterdam, The Netherlands
>     Tel: +31 20 512 1951 Fax: +31 20 512 1954 Mobile / SMS: +31 6 28 597791
>
>
>
>
>
>
>
> --
> Mark J van Raaij
> http://webspersoais.usc.es/mark.vanraaij
> http://www.ibmb.csic.es