• • SVA Brewer With Over 100 Brews From United States of America
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• • SVA Brewer With Over 100 Brews From United States of America
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I have the same capacity and diameter kettle Paul. My boil-off varies from brew to brew depending on the weather etc so maybe wait a few brews before changing the BIABacus default too much. As josh has pointed out, a lot of things can affect the rate on any one day. I always prefer having to use a bit of top-up water at the end rather than the reverse so under-estimating evap rate is better than over-estimating it.

• • SVA Brewer With Over 100 Brews From Australia
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Evaporation rates variance

On the rolling boil thing, what you are describing sounds great Paul. You don't want a simmer going on nor do you want the wort jumping out of the kettle.

Going back to whether you should adjust your evaporation rate. Here's why I reckon, "No!"

As with anything in brewing, you can't trust the numbers on one brew. Evaporation numbers can vary wildly. Here are the evaporation rates in litres for 1.5 hours on 6 brews of mine done over three consecutive days...

9.0 L / 15.1 L / 9.3 L / 9.6 L / 8.0 L / 7.2 L

So what does that tell me? The main thing it tells me is that a single brew's measurement can tell you nothing much at all . For example, perhaps I made a measurement error on the second brew - who knows for sure? See how the last two brews had less evaporation than the first four? The last two brews were done on calm days not windy days like the first four brews.

The final thing that the collection of numbers tells me above is that the BIABacus default works almost perfectly for my kettle - on average. Until you have such a collection, over-riding any defaults is probably not going to serve you well.


PP

• • SVA Brewer With Over 100 Brews From Australia
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paulg wrote:that 2nd brew of yours is definately very different to the others in terms of boil off??

It is a wide discrepancy on that brew. Probably a measurement error of some sort as I did 6 side by side double batches in those three days recording many sets of measurements for an experiment. With that many numbers, you'll always get some wild figures. It also was an IPA so the larger hop bill had a little bit to do with that measurement discrepancy I believe - long story.

Mind you, I still get some wild figures occasionally no matter how accurately I think I have measured and double-checked. This is why I never trust anyone that says they always hit all their numbers dead on. Even if you could measure perfectly, there should be variance between brews as water, weather and grain extract potential will all vary from day to day or batch to batch. The most amazing brewers are those who always get the same 'efficiency' regardless of whether they are brewing a 1.040 beer or a 1.060 beer.

Posts like that are claiming the impossible. It's a common belief that you will be able to brew consistently and always hit your numbers in home brewing but it's just not the case. Even the largest commercial breweries have to make adjustments from brew to brew to correct for inconsistencies in ingredients etc. Our inconsistencies should be much greater.


PP

• • SVA Brewer With Over 100 Brews From Australia
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OhOh.. I hit my numbers pretty exactly on my first (and only.. so far) BIAB. So, I guess you don't trust me But, that's OK. I did, none the less. Next time is anyone's guess.

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Bill. If it happens ten times in a row then I won't trust you .

And don't worry, you are not alone in getting right numbers . I just wrote in another thread that the BIABacus auto-estimates for evaporation, trub/s and efficiency/s seem to be getting most brewers in the ball-park if not hitting a home run like yourself. That's a pretty good thing. Having good numbers to work from in the beginning is the first step.

The next step, I think, is to learn not to worry when you don't hit your numbers.

For example, if your into fermentor numbers didn't hit on a single brew, you'll never know whether there was really a problem unless you took some pre-boil and/or EOBV numbers as well.

If you had taken those 7 measurements (pre-boil volume and gravity / end of boil volume and gravity / volume into fermentor, kettle trub volume and fermentor gravity) then you will be ahead of the other brewer as you will have a series of double checks and therefore know if there even was a problem on that brew but, that is all you will know.

The next stage is to brew again, nearly always several times to see if the pattern repeats itself consistently.

If it does, the final thing to ask is, "Should I be changing my defaults or is there another problem going on here that I am missing?"

Not a good thing to read I suppose in these days of instant answers ,
PP

• • SVA Brewer With Over 100 Brews From Australia
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