Measuring batch size

This question mostly pertains to using different calculation tools, but also because I'm into keeping really detailed notes to help improve my beers down the road.

So when do you guys typically measure what your "batch size" is? Post-boil in the kettle? What's poured into the fermenter (if straining this reduces from the post-boil volume)? What you rack to secondary/bottling bucket?

I've noticed that there's often quite a bit of trub loss from one brewing stage to the next. So for example, if I'm calculating IBUs and there is 5.5 gallons in the brew kettle, 5.0 gallons after straining into fermenter, and 4.75 gallons in the bottling bucket, which measurement do you use?

I have been wondering the same thing, good question, subscribed for the response

For IBUs, you would use the post-boil volume, pre-straining into fermenter. In your case 5.5 gallons.

IBUs aren't affected by changes in volume post-boil. They are effectively "set" at the boil stage.

Hope this helps.

To answer your larger question, I would consider batch size to be what you have post-boil. Everything that happens in the boil process should be calculated relative to that.

Good question, Ive been going with what ends up in the fermenter as my batch size. I also don't worry about volumes relating to heat expansion....I figure if you measure the same thing each time it won't really matter. So long as you measure consistently so that you can hit your numbers each time.

For example I do the same boil/etc for all my beers, but end up with larger losses from kettle to carboy on hoppy/heavy beers like IPA. On IPA I end up with a bit less in the fermenter but I still hit my predicted OG if I boil a 1.054 Nut brown, I just get a few liters more Brown into the fermenter.

Does that make sense? Anyway, Im curious what others will have to say. Maybe I'll start measuring kettle and post straining volumes just to see what happens. I never really thought about it before

As said, post-boil volume is what affects IBU.
Fermenter volume is important for proper pitching rate.

Thanks for the responses guys, they all make sense.

How about when reading a recipe or writing your own out? I think for the most part I'm using post-boil for that as well.

More technical, I'm pondering about SG readings and I think my head's still a bit tired from a crazy busy weekend. For all grain, if you boil down to different volumes would the OG be the same? For example if you did two identical batches, except that one boiled down to 5.5 gallons and one boiled down to 6.0 gallons, would they produce the same OG reading?

The way I call it:
Batch Size is what goes into the fermented.
Boil volume is the average volume during the boil. This is used for utilization calculations. IBU is calculated based on the utilization and the change in volume from boil to fermented if/when topped off.

OG is the gravity of what ends up in the fermentor. It is very important that you measure at that stage to get your entire brew house efficiency. (in your example the same wort boiled down to 6.0 and 5.5 would not have the same OG)

They sure wouldn't! Sugar stays and water evaporates....that's why boil off is important, how much you boil off on your system directly effects your OG. The concentation of sugar increases as volume decreases, therefore higher OG with higher boil off.

Same deal if you are topping off. You might have 2.5 gallons of 1.100 wort in your kettle, but you add it to the fermenter and top off to 5 gallons your OG is 1.050

Odin_Brews said:

They sure wouldn't! Sugar stays and water evaporates....that's why boil off is important, how much you boil off on your system directly effects your OG. The concentation of sugar increases as volume decreases, therefore higher OG with higher boil off.

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Thanks. Like I said, I'm certainly not thinking as straight as usual, lack of sleep (dang children). Definitely makes sense, I guess I could have used one of the many calculators I have bookmarked to figure that out. I've only done two all grain/full boil batches, but I made sure to adjust the vigor of the boil depending on pre-boil volume and how quickly it boiled off. With my last batch I had 6.75 gallons before boiling and ended up getting pretty close to 5.5 after 60 minutes. I made sure to bring the boil down to a gentle boil for the last 30 minutes so I finished at 5.5.