So my tried and true kettle finally had to be replaced and I am planning for my first batch with the new kettle.
My new kettle is larger and has a smaller height:width figure. Since it is proportionally wider, should I expect more evaporation? I will be brewing one of my regulars to help me dial it in but hoping to make small adjustments beforehand regarding preboil volumes based on expectations.
You will likely see more evaporation in the same time frame with a wider kettle. More surface area and all that. I don’t have any numbers that would help you calculate it (falls into an area of math I have forgotten or never really learned :
).
Without the before and after dimensions I don’t think it can be calculated (even if you remember the formulas). My SWAG would be “more but not a huge amount. Maybe a quart/hour.” Complete guess on my part though.
Paul
Thanks. I will probably just plant to collect about a quart more from my runnings and see where I end up at. The beer is 5% ABV so if the gravity swings a couple points either way based on volumes it shouldn’t be very noticeable.
You could also just reduce the heat applied to the kettle to reduce the boil-off rate. Measuring boil-off rate is easy if one knows the dimensions of a kettle. All one needs is a stainless steel or non-toxic plastic ruler. The volume of a cylinder in cubic inches = 3.14 * radius_in_inches2 * height_in_inches. There are 231 cubic inches in a U.S. gallon; hence, the volume of wort in a kettle in gallons = 3.14 * kettle_inside_radius_in_inches2 * distance_in_inches_from_the_bottom_of_the_kettle_to_top_of_the_wort / 231. The boil-off rate can be controlled by taking periodic readings and extrapolating the lost in wort volume over the boil length. If the extrapolated loss is too great, reduce the heat and recheck in 15 minutes. If the loss is too low, increase the heat and recheck in 15 minutes.
One last thing, the height of one gallon in a kettle in inches = 231 / (3.14 * radius_in_inches2).
+1
Thanks all. I have that exact formula ready to auto calculate in Excel using cm to measure pre and post boil volumes. Actually, my post boil measurement is after cooling so I just include evaporation as part of my losses. I suppose I could start taking actual ‘post boil’ measurements.
I probably won’t be messing too much with the burner level because I like to keep it consistent from batch to batch. Using this method with the old kettle, I was consistently get post-boil volumes within 0.06 gallons of each other (after cooling).
For those who want to know what the cooled volume will be when measuring a liquid at or near boiling, a liquid expands by approximately 5% at 100C/212F.
cooled_volume_of_wort_in_a_kettle_in_gallons = 3.14 * kettle_inside_radius_in_inches2 * distance_in_inches_from_the_bottom_of_the_kettle_to_top_of_the_wort_at_100C / 242.55
Good to know. Thanks. I think beersmith has a 4% cooling loss as default…
The value is actually more than 4%, but less than 5% (Brew Smith is taking the floor whereas a I am taking the ceiling). That’s why I prefaced the value with “approximately.” Four percent will work as well, but the actual measured value will be slightly less than the computed value whereas it will slightly more than computed value when using 5%. I prefer to have slightly more than slightly less wort because I use whole hops.
Thanks. Since I am taking a post-cooling measurements and imputing that in Beersmith, I can’t truly know my evaporation rate I suppose. I am basically getting one sum of losses. I will need to rethink my process and possibly start doing a true post boil, pre cool measurement.
Mark, I am so glad that you re-posted these equations. I know you have had them up before, but I was unable to find them recently when I was trying to figure out if I could handle a larger batch in my kettle. In the end, the online calculators I found were correct and it was a simple math error on my part that I only found through posting here. I have copied and saved your equations for future reference though. Thanks again