I have two sets of equipment and so was able to do two recipes per day for the last three days. Each boil (recipe) resulted in two batches, one chilled and one no-chilled.
Doing so many brews at double volumes created a measurement opportunity I didn't want to let slide by. (In hindsight, I wish I did. Taking so many measurements form two brews running almost simultaneously is not very relaxing
). Here's some things I thought I'd measure..
1. Measurement Discrepancies or Variances
2. Difference in gravity at 30, 60, 90 mins and mash-out. (Didn't think of this until Day 2).
3. Variance between different "mash" efficiencies.
4. Active sparging versus BIAB's innate 'passive' sparge.
Measurement Discrepancies or Variances
I'll attach two spreadsheets to this post. One is a summary. The other contains all the raw data and any adjustments made. (These will be like heiroglyphics as I wrote the spreadhseet as I brewed and thought of more things
)A few points to note...
1. My refractomter proved to be totally inaccurate on day one. Continued using it on days 2 and 3 for 30, 60 and 90 min mash measures.
2. You'll see many other measurement discrepancies or variances. Whilst a single brewer doing measurements on two side by side brews staggered only 10-20 minutes apart will obviously result in several errors, I didn't find the errors or discrepancies surprising. The variances reflect my past experiences.
3. Many other things to comment on here but these are 'fine' detail.
Difference in gravity at 30, 60, 90 mins and mash-out.
Based only on refractometer readings, we can easily see a steady increase in gravity over time. While more figures are needed, any time I have measured this in the past has shown the same thing - a 90 minute mash is certainly more efficient than a 60 minute mash.
Variance between different "mash" efficiencies.
As water/wort expands exponentially, I think it is very hard to take good volume measurements at the boil start and boil end. On some of my measurements, I didn't have time to take measurements immediately at the boil end. Some had to be taken a few minutes later. There is much swelling and contraction around boiling point so it's probably not the ideal place to take volume measurements.
Another thing is that the BIABAcus2's variable efficiency calculation (based on the CE Calc) is predicitng way under actuals. It also doe not consider mash length.
Many factors to be considered here for BIABacus 3
.Active sparging versus BIAB's innate 'passive' sparge.
On these 6 brews, I was unable to find that sparging makes more than 2% difference in efficiency. On such big brews, it took a hell of a lot of inconvenience, effort and equipment. I am never sparging again
. Some Basic Conclusions
1. The above confirms, once again, that a single instrument can't be relied on.
2. The above confirms, once again, that measurements from a single brew can't be relied on.
So...
Clever ways have to be thought of where many brewers can focus on a single measurement and submit their results. I'll ask Kostas if he can come up with a way of dong this while BIABacus3 is being developed. I'm happy to do a few measurements on a single brew but never want to do this many measurements again
.Even, if we collect the best average figures around, see 1 and 2 above
.The good news is that I brewed 240 litres in 3 days and will now have some beer in my fridge
.PP
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. You say the sparged batch is lower gravity at the start of the boil which would mean sparging is less efficient. Have you got any "end of the day" numbers? e.g. How much you ended up with in the fermentor and at what gravity and also kettle trub?
. The way I'm reading your posts, you seem to be getting lower gravity from your sparged brews 
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