First BIAB comes up short

[Headpocket]

I attempted my first BIAB yesterday from a recipe I found online. A one gallon Pale Ale. Although I followed the instructions exactly when I finished I was only left with about half a gallon. Either the recipe was wrong or I've got my quantities of water incorrect! I put this in a fermentor and it's now bubbling away quite happily. My question is would it be a terrible idea to now open the fermentor and top it up with water to give me a full gallon?

 

[BeerisGOD]

I think ud be ok with bottled water, but poured slowly down an angle of the FV.

 

[photek1000]

I would check your OG against what you were expecting, if it's the right strength but short on volume I'd leave it be and then work out what area went wrong, and see what it tastes like.

If the OG is way over there are calculators for working out how much to dilute by.

I brewed short by miscalculation on my first BIAB and first 3V All grain brews, I just left them alone as the OG was pretty much spot on and made notes on how it effected taste once drinking.

 

[MyQul]

You can dilute at any time. When it's finished fermenting, take a gravity reading and use this dilution calc to dilute appropriately

https://www.brewersfriend.com/dilution-and-boiloff-gravity-calculator/

 

[Headpocket]

Thanks Gents for the useful advice.

 

[YourBrew]

I hate to be "that guy", but I'd really avoid diluting it, there's just much risk on it:
- you can easily contamitate the beer
- you can oxigenate the beer
- you can change the taste

To my experience it's just not worth it and, like someone already said, taste it and take notes, try to figure out what went wrong and change whatever you need for next time.

 

[Fil]

as above let gravity guide you as to any water additions to dilute, AG brewing is a case of refining your technique based on earlier results with the equipment you use. adjust the volumes of strike and sparge liquor for your next brew according to the results of the first and you should be much closer to all your targets, the subsiquent brew will be even closer too..

 

[Sandimas]

Did you measure the OG before pitching the yeast, if so how far was it out? i.e. have you brewed a stronger beer with less volume than you originally intended, or the beer as intended just less volume? If the former, I'd top it up.

As others have said, it'll take a few brews to refine your technique, work out what sort of mash efficiency you're getting etc. I do BIAB and I don't really bother with the calculations, just ensure my final volume is as per the recipe by topping up at the end of the boil: my efficiency is usually spot-on (68%) so I get what I intended to brew.