SG vs OG Off

[TBC27]

Hi fellow brewers! My last two brew days have involved my SG reading right at the start of the boil being higher than the recipe states. Yet, my OG going into the fermentor is below what the recipe states. These seem backassward to me. I would expect my OG to be higher than the recipe states. Anyone have any ideas why this is happening? I use a propane burner and my boils are by no means weak but that was where my brain initially went when trying to identify a reason.

I do all grain. Batch sparge. The brew session today was a Founders Red Rye clone and my mash temp hovered between 153 and 151F.

 

[doug293cz]

Couple of things can cause that:

1. Boil off less than recipe assumes, so that post-boil volume is high, which lowers OG.
2. First runnings and sparge runnings not completely mixed. This can cause either a too high, or too low, pre-boil SG reading depending on where the sample was taken. Complete mixing takes much more effort than you think.

Brew on

 

[TBC27]

Couple of things can cause that:

1. Boil off less than recipe assumes, so that post-boil volume is high, which lowers OG.
   
2. First runnings and sparge runnings not completely mixed. This can cause either a too high, or too low, pre-boil SG reading depending on where the sample was taken. Complete mixing takes much more effort than you think.
   

Brew on

I don't think #2 is the culprit. I stir frequently as the wort comes to a boil and also wait a few minutes after the boil starts to take a gravity reading.

If #1 is the issue that would mean I need to decrease my efficiency when formulating recipes, correct?

 

[doug293cz]

I don't think #2 is the culprit. I stir frequently as the wort comes to a boil and also wait a few minutes after the boil starts to take a gravity reading.

If #1 is the issue that would mean I need to decrease my efficiency when formulating recipes, correct?

No, just lowering the efficiency alone will just give you lower OG, all else being equal, You want to have less wort at the end of boil, so that the sugar is more concentrated. You can do a couple of things:

1. Reduce your total brewing water (which will decrease your efficiency a little.) Then you will have less pre-boil wort at slightly higher SG. Then even with low boil off, you will have less post-boil wort at a higher OG
2. Boil longer and/or harder, to increase boil-off and decrease post-boil volume and increase OG.

A good consistency check on your measurements is to see if:

Pre-Boil Vol * (Pre-Boil SG - 1) = Post-Boil Vol * (Post-Boil SG - 1)​

If they match, there is a pretty good chance your measurements are ok. If they don't match, then one, or more, of your volume and/or SG measurements has significant error.

Brew on

 

[kh54s10]

You really need to work backward. You need to get the right volume at the right OG into the fermenter. If your OG is low but you have the right volume, you have to figure out why. The usual culprit is poor crush. You can work on that 2 ways. The best way is to get a better crush. Second best is adjust the input for your expected efficiency in your recipe software to give you more grain which will increase the OG. With a good crush and still low OG, you need to adjust expected efficiency until what you start with gives you the OG you want. A bit hard to describe.

 

[TBC27]

No, just lowering the efficiency alone will just give you lower OG, all else being equal, You want to have less wort at the end of boil, so that the sugar is more concentrated. You can do a couple of things:

1. Reduce your total brewing water (which will decrease your efficiency a little.) Then you will have less pre-boil wort at slightly higher SG. Then even with low boil off, you will have less post-boil wort at a higher OG
2. Boil longer and/or harder, to increase boil-off and decrease post-boil volume and increase OG.

A good consistency check on your measurements is to see if:

Pre-Boil Vol * (Pre-Boil SG - 1) = Post-Boil Vol * (Post-Boil SG - 1)​

If they match, there is a pretty good chance your measurements are ok. If they don't match, then one, or more, of your volume and/or SG measurements has significant error.

Brew on

Awesome! Thanks!

 

[TBC27]

Awesome! Thanks!

387 vs 378 Is that difference drastic enough to warrant a process change?

 

[doug293cz]

387 vs 378 Is that difference drastic enough to warrant a process change?

That's about a 2.5% mismatch, so not too big a deal. And if the numbers don't match, it's not necessarily a process change that's indicated. All it may need for resolution is better measuring accuracy. Some things, that might be categorized as process changes, that affect measurement accuracy are:

• More thoroughly mixing wort prior to taking pre-boil SG samples. You really have to mix aggresively.
• Better cooling of hydrometer samples prior to taking readings.
• Taking pains to avoid water evaporation from hot refractometer samples (evap will raise SG values.)

Brew on