Before I got my newer washrack built I let my beer gauge when it is to cold. If my beer shushed up, it was to cold to be putting water on them. Yesterday it was 30* and I got it up to 65* at one time in my washrack area before I turned down the heat. Saying, that is to hot given you are going to kick them back out in the cold.
I think good comon sense plays into all this. Check the shiver factor of your calves when rinsing in the cold one, and two, if you end up sick too that won't be much of fun way to head to a show.
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