Strike Water Calculation

[Spearson92]

Hi all,

New member here asking for some feedback on where I went wrong/how I can improve. I did my first AG BIAB yesterday which was a Doom Bar clone normal batch of 23L, but I halved the recipe due to equipment. All was going well until I measured my OG and it came out at 1030/1031 (should be 1040).

I think I've already self-diagnosed the reasons why, the main one being too much water to start with. I followed a no-sparge guide that said: batch (2.63G) + boil off (1G/hr = 1.45G for 85 mins boil) + grain absorption (roughly 0.1G/lb = 0.43G). So total should be 4.51G strike Water for the recipe? When I put the grain in I thought it looked a bit watery but carried on.

Am I right in saying I've used too much water initially which has diluted it and dropped the OG? During the boil the lid was partially on to maintain the boil so perhaps also some evaporation issues also played a small part. In terms of fixing it I guess I could have boiled for longer or added some DME but didn't have any. I guess I could have also taken an earlier OG reading which may have helped to notice the problem earlier.

Am I on the right lines here? And if so how do you guys calculate the water required?

Many thanks!

 

[Spearson92]

Forgot to say 15L went into the fermenter which makes me think there was maybe too much water to start with?

 

[strange-steve]

So you were aiming for 11.5L at 1.040 but you got 15L at 1.030, is that right?

If so then yes you've used too much water which also accounts for the low OG (you'd probably have been about 1.039 if you'd hit the correct volume). The next step is to work out where your calculation is incorrect (sorry I don't know imperial measurements):

Batch size + grain absorption + boil off + boiler losses = total water

Grain absorption is typically around 1L/kg.
Boil off is dependent on your particular system so take good notes and you can dial this in, but around 2 - 2.5L/hr is a reasonable starting point.
Boiler losses will depend on the recipe, the amount of hops, dead space, how fussy you are about transferring trub into the FV, but for me it's usually about 2L for a 20L batch.

It looks to me like your boil off was much lower than you calculated for. It's your first AG so don't worry about it too much, it'll turn out fine and with each batch you'll get a little closer to your target numbers (in theory at least, I've brewed about 90 batches and my numbers are still off sometimes).

One tip is to use a little less water than you think you need, because then if you're under volume at the end all you have to do is top it up with some pre-boiled water. It's easier to dilute than it is to concentrate.

 

[Spearson92]

Thanks strange-steve! Good to have my suspicions backed up. I reckon from what you're saying, I've got the extra from the boil. The guide I was using reckoned about 5.4L for the 85 min boil. Using 2L/hr is about 3L for the 85 mins, which probably accounts for 2.5L of the excess water, then a litre here and there for grain absorption/equipment/trub etc.

As I did half batch, I'm going to do the same again so I can try and nail the method using the same recipe.

 

[jeg3]

Boil off of 1 gallon / hour looks high to me. Typically it's 3l / hour although at the minute with low outside temps I'm getting 2l / hour boil off

 

[jeg3]

As @strange-steve says it's easier to dilute an overshoot on OG, but in the past I have added a quantity of cooled boiled DME to the fermentor via a calc for a really low OG with good results.

It was a while ago though when I was getting to grips with AG. Doesn't happen anymore

 

[Brianbrewed]

What kind of system are you using?

 

[GeorgieV]

Another thing to keep in mind is to check if the instructions are in US gallons or imperial gallons. The difference is about 20%.

 

[Spearson92]

Thanks guys! Yeah think I need to stick to metric which might help along the way. From everything you guys are saying it's sounds far more reasonable boil off rate.

I'm just using a 23L stock pot for the mashing/boiling.