Richard, nice post from SP above
His last line especially nails it...
There are some formulas for the expansion of water at different temps but, they fail dramatically if my memory serves me correctly, when you get to about 4°C (4 degrees above freezing), as water does some really weird things at around that temp. But, that bit of trivia is beside the point as SP has said.
To expand on what SP has said, and let's just deal with water, not wort, the expansion of water is exponential. In other words, the higher the temp the faster it expands. In the BIABacus, we could have used a dubious formula (there is one) where your volume would vary per degree of temperature. That is not a good way to go however for several reasons...
1. It makes the user respect unimportant numbers too much.
2. Measuring tiny differences in volumes caused by temperature is impossible on small systems
AND large ones.
3. As SP said above, sweet liquor will not necessarily behave the same way as pure water. Who knows?*
I think this all gets down to
Number Respect and Disrespect. No commercial brewery is able to input the same amount of water, malt etc on each brew to get the same result. Every single batch requires adjustment. Craft breweries have the same problem and, if the beer is 'interesting', the problem gets harder. We home craft brewers have the same problem again but harder still...
There is a common myth amongst home brewers that you can make beers repeatable. This is incorrect. For a start, evaporation cannot be predicted perfectly prior to a brew day so, we already have 'prediction' problems. But, if we set our defaults sensibly (as the BIABacus aims to do) we can adjust for that easily.
The real issue though for us tiny brewers (and even for the massive commercial brewers) is that our ingredients are never the same day to day (besides yeast - hopefully!). Water can be made consistent to a high degree (eg RO and salt additions) but malts and hops are a different story. For a start, this week's bag of "pale ale" malt from a maltster might be quite different from next week's bag from the same maltster. This is why they issue a specification sheet for every malting they do; even they do not have total control.
Hops are much worse though. You already know that alpha acid percentages of the same hop can vary greatly from one year to the next. Here are two other things that very few people know...
In the same country, the same variety of hop can also vary dramatically from one region of the country to another in the same year! (This happened with some sort of Hallertau in Germany a few years ago).
The other big one is something hardly anyone knows about, even commercial 'craft' brewers. A new hop variety might produce unique/fantastic flavours in its first five years but, as the vine matures, these unique/fantastic flavours are sometimes lost. I stumbled across that info in a podcast about a year ago and it really struck me as Amarillo used to be a real favourite of mine but I have never been able to brew a great all amarillo beer for about 4 years now. (Last night and the night before here in Perth, there have been some commercial craft brewer get-togethers. This info was news to the brewers I spoke to and made a lot of sense to them.)
So, to sum up, there is so much out of our control. There is very little info out there on just how little control we have. The paradox though is that the more info we have on what is out of our control, the more comfortable we can get in our brewing. e.g. Q. The amarillo ale I brewed last year tasted way better than this years? A. Maybe this year's amarillo is a crap crop? Did I save some of last year's in my freezer to compare?
While most of this post has talked on how little control commercial or home brewers have in many areas, that last paragraph shows one area where we home brewers can have an advantage. Commercial or craft breweries can't afford to store hops in a freezer from one year to the next whereas we can. (I've never thought of this before as I have been, until the last year, very poor in labelling my hops!) If I had had the knowledge written above previously, I would have saved myself brewing quite a few unsatisfactory APA's. I would have been on to the fact that maybe amarillo no longer produced tremendous passionfuity aromas etc and ventured into galaxy or citra more.
Oops! That is a very long ramble sorry Richard. Hope there aren't too many spelling mistakes or grammar errors but I have to race!!!
Cheers mate,
Patch
*One thing we do know on sweet liquor or wort, is that it does not weigh the same as water. (I can't remember if BIABacus PR1.3T deals with that but, later as yet unpublished versions do).
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