Tuesday, October 15, 2013

How long does it take to chill colostrum in a refrigerator?
Why are we interested in chilling colostrum? We know that the time required for bacteria in colostrum to double (generation time) increases as temperature decreases. Thus, one simple way to reduce bacteria counts in stored colostrum is to chill it from cow body temperature (slightly over 100F) to typical refrigerator temperature (around 40F).

 Estimated generation times for coliform bacteria in colostrum are:
 20 minutes @ 100F, 
150 minutes @ 60F, 
12 hours @ 50F and 
greater than 24 hours @ 40F.

Using two used refrigerators in good working condition in the garage of our vet clinic during August I set them up with temperature sensors and data loggers. I chose to load them with selected volumes of colostrum in different kinds of containers at either 90F or 60F. 

So, how long does it take to chill colostrum to 40F in a refrigerator?

1. How warm is the colostrum when it goes into the refrigerator?

If we load 10 2Qt. nursing bottles at 90F they will arrive at 40F in about 24 hours!
If we load 10 2Qt. nursing bottles at 60F they will arrive at 40F in about 13 hours.

2. How much colostrum goes into the refrigerator at one time?

Assuming the colostrum starts at 90F in 2Qt. nursing bottles the time to 40F looks like this:
     Bottles  Gallons  Hours           Hours to Chill
                                 to 40F          to 40F if start at 60F
          2          1          10.7                    7.4
          4          2          16.0                    9.9
          6          3          18.9                   11.7
          8          4          21.2                   13.1
          10        5          23.7                   13.2  (80% reduction in chilling time)

My chilling times for bottles were measured with the bottles all pushed together as they are typically in an on-farm refrigerator.

3. What size container is used for the colostrum?

I used 5-gallon pails, 1-gallon bottles and 2-quart nursing bottles. Chilling times for all containers were very similar with a trend to slightly more rapid chilling (in 5-gallon lots) in smaller containers. Container size has only a marginal effect on chilling rate in this situation.

Bottom Line for low-bacteria count stored colostrum
  • Start with a low inoculation level - clean
  • Chill rapidly (no more than 30 minutes) to 60F before refrigerating or freezing.

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