hashie wrote:rocket58 wrote:The Calculator says it is on kettle circumference not opening circumference and your and my data back that up. Interesting to see it proved.
This would also suggest that a lid will not reduce boil off?!?
Yep hashie, despite a lot of home brew folk-lore, putting a lid half-way or 3/4 way over your kettle is not going to make much difference. Doing this will only trap a tad of condensation that will drip back into your kettle. The majority, of course, takes the very easy (non-pressure) route out. Unless you cover your kettle fully (or 90-95% fully) you will see little difference in volumes after a boil.
You can easily test this with a saucepan on your stovetop.
There are many questions to be answered here though that haven't been. A few I have never heard a decent answer too are...
1. If one of the most important functions of a boil is to boil off "nasties" then how much do we need to boil off?
2. What is the best kettle shape for a home brewer to boil off nasties? What if they do too much or too little?
3. Why do commercial kettles have a funnel at the top? Is it soley so as to extract evaporation more easily (in other words a 300 mm chimney is a lot more sensible than a 5 m one) or does this create the perfect boil-off/nasty ratio?
Home-brewing software suggests an average of 15% evaporation rate based on initial volume but we all know that the evaporation rate stays the same regardless of volume.
I think that before we start worrying about trying to conform our evaporation rates to the fictitious 15% (which is way higher than commercial breweries) we really need to answer those 3 questions above.
The only software that suggests using kettle diameter (meaning the widest surface area of your wort in the kettle during the boil) as the most sensible formula to use to determine evaporation rate that I have seen has been
The Calculator.
I'm actually a tad baffled where that 15% standard used in other software comes from.
PP
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