Hi There, Can someone explain to me why batch size (fermentor) changes OG, IBU, FG, ABV and SRM. Surely if I have brewed a batch in the same kettle and transferred into fermentor it should be the same whether I decide to transfer 24 litres or squeeze out an extra litre? Its the same batch of beer ?
Because all of those values are a function of boil off. There is a difference between boiling 5 gallons and having 1 gallon evaporate (condensing the wort), and having an ending volume in the kettle of 5 gallons and throwing 1 gallon away.
Because the drop-down isn't changing the number, it's changing the volume type and keeping the value the same. Like yooper said, for your scenario Batch: 24 liters. Postboil: 25 liters. 30 preboil. 70% efficiency. Target fermenter means you have 70% of the fermentables at 24L, and (70*(25/24))=73% at postboil, since youre gaining 1L. The gravity is going to be the same at postboil and batch size, as is the srm and IBU. Now you change the target from fermenter to kettle, without changing any of the other inputs. Target boil means you have 70% efficiency at boil (but at 24L still since it's just relabelling the existing batch input and hiding the post boil volume). Vs the 73% at boil for the above. If instead you change target to kettle, at 25L, and kettle efficiency to 72.9x% then they should all be the same.
OK I probably worded that wrong. I understand boil off rates and grain/hop absorbtion etc.and how they affect the values. Im not a technical man but more of a practical one so I know how to brew a good beer, understand so much of the science but some things I dont get. Lets say I have just brewed a beer and chilled it to 21C ready to go into the fermentor. Based on your recipe editor... I transfer 25 litres into fermentor IBU =76.31, OG = 1052, ABV= 5.49 SRM=4.76 I transfer 26 litres into fermentor IBU =74.44, OG =1050, ABV=5.28 SRM= 4.63 To me the brew was finished when I chilled down and anything in the kettle is the same IBU, ABV, OG and SRM If I choose to bottle 10L, 15L or 25L to me it should be the same brew and same values. Its like eating a cake, once it is baked you have a slice or 5 and it is the same. Priceless, you said in your post the gravity is going to be the same at post boil and batch size as is the srm and ibu Post boil values are fixed and cannot be changed but if I change the batch size then as above it changes all the values. I appreciate your time and you must shake your heads some times at some of the post you get, I am trying to educate myself a little more in the science of brewing so please be gentle (lol), Cheers.
Yes- but remember the volume. In the first example, it’s assumed that you boiled off an extra liter, therefore condensing the wort a bit more while in the second example, you have more wort which is assumed to be less concentrated (not as much boiled off).
If you decrease your boil size, and keep efficiency and postboil volume the same, then you're telling the software that your throwing away additional wort between post boil and entering the fermentor. Because the efficiency is set to brewhouse, this results in a change in postboil properties, since brewhouse is tied to fermentor. If you use the kettle efficiency, then the efficiency is tied to the postboil kettle volume and then the volume in the fermentor is irrelevant. Side note, you mentioned bottling. Packaging volume is completely irrelevant to all of this, and is separate from batch (starting fermentor) volume.
If there's still confusion, I'll pull up a recipe and see if I can provide real examples instead of theoretical descriptions.
