Struggling to hit OG... some advice?

[SimonB]

Hi all

I'm a BIAB brewer. While I thought I was starting to get this brewing lark waxed, there is one area where I still struggle... hitting my OG.

While I'm always very close to the preboil gravity, I cannot for the life of me get consistently close to my OG. The last brew I did, I was aiming for 1.070 and I was 12 points off. Now the only thing I can ascribe this to is the wrong predicted boil off rate that I had plugged into Beersmith.

No what confuses me is I tested two boils, just using water so I could get some idea of boil off with my new 28l electric kettle. What I got there was around 4 litres per hour which seems about normal. But the calculated boil off I got based on the difference between SG and OG was 2.6litres / hour, which was a little less than the actual boil off at 3litres.

My questions are:

What am I doing wrong? My environment where I did my tests were little different from my actual last brew? Or does wort show a different boil off to water? Surely not?

What other factors am I missing?

If boil off's are so variable, which one to plug into Beersmith? My thinking is I should probably use the LEAST amount of boil off likely in my kettle, because then I can just add more water if the boil-off is excessive. In my mind, too little boil off is harder to correct because of the problems with the hop additions, and the only option then open to me is the addition of DME.

Your advise would be appreciated. Thanks

 

[ChuckO]

Boil off rate is affected by the surrounding conditions. Air flow, temperature and humidity all change the actual boil off rate. I ran a couple of tests and then took notes from my first few brews after finishing my system. I then used an average in BeerSmith for my calculations to determine pre-boil volume. When I am about half way through the boil, I look at the volume remaining and then adjust the heat to either increase or decrease the boil off. Usually I have to make the boil slightly more vigorous for the last half in order to hit the final volume. By changing the heat I can keep the boil time the same for hop utilization but still hit the volume.

 

[beergolf]

If you keep track of your boil off over several brews, you should be able to pretty much hit it every time. There are some variables. like temp, humidity, etc. that will slightly effect it, but you should be close. I always check where I am at the half way point. I marked my spoon so I can use it to check how much I have at the half way mark. If it looks like I am not boiling enough off I adjust the boil time so I end up where I need to be.

Just takes a little practice.

 

[IrregularPulse]

It'll take a few brew sessions to dial in your specific system. Just take good notes until you get a handle on it.

 

[SimonB]

Thanks all for the advise

If it looks like I am not boiling enough off I adjust the boil time so I end up where I need to be.

How does this (if at all) affect your hop additions? I mean hop bitterness depends both on boil volume as well as boil time? Or do you assume all the bitterness that has been added at the beginning of the boil has been imparted to the wort, so all that really matters at the end is the volume?

 

[beergolf]

Thanks all for the advise



How does this (if at all) affect your hop additions? I mean hop bitterness depends both on boil volume as well as boil time? Or do you assume all the bitterness that has been added at the beginning of the boil has been imparted to the wort, so all that really matters at the end is the volume?

Most of the brews I do have a bittering addition, which increasing the time will not make much difference. Then most of my other hop additions are always 30 minutes and under, and for my IPA's all additions are 20 minutes and under. So if I add some time to get some additional boil off it does not effect the later hop additions. I know where I have to be at the 30 minute mark to reach final volume. Once I am there, I can continue with my hop additions.