Wyeast: When Yeast Should be Harvested

http://www.wyeastlab.com/com-yeast-harvest.cfm

When Yeast Should be Harvested
The timing of cropping will have effects on the quality and density of the slurry. Consistent timing of harvest will help maintain the desired characteristics of the culture.

•Cylindroconical and Dish Bottom Vessels (Bottom Cropping): Yeast should be harvested once the temperature has dropped below 40°F (4°C) and trub has been discharged. This will insure a large yield of clean, homogenous slurry.

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Anybody have any thoughts on Wyeast's suggestion for harvesting yeast from a conical. I basically do it at my fermentation temperature.

Cheers,

I'm no expert, but as I understand it, the least flocculent cells are also the highest attenuating ones that stay active and finish things up when most of the culture has dropped. The idea is that if you harvest at fermenting temperature, you are leaving a larger percentage of these high attenuating cells behind and over generations that will alter your yeast culture and end up with a lower attenuation rate. Crashing to <40* will cause those cells to flocculate out, making them a part of the harvest thus keeping the traits of the original culture more inact.