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FG and CO2

K

ksga

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Hi experts

I've been doing a couple of brews, using Beersmith to build the recipes - awesome :D
I have one question though. Does Beersmith take the CO2 in the fermenting/fermented beer into account when estimating FG?

If not - should I then shake the beer to release some of the CO2 before measuring SG's and FG?

I'm asking because I'm coming in a bit high on FG, and are looking for sources of error. It could of course just be that I'm lacking oxidation when starting fermentation and therefore have constant under attenuation :(
 
Carbonated beer would give you an artificially high SG reading as the bubbles will cling to the hydrometer and buoy it up.  If the beer is not carbonated yet, then the presence of naturally dissolved CO2 has a negligible affect on the reading.  You can see this in that your hydrometer will not have gas bubbles attached to it.

You say you are consistently high on FG, but how high are you?  There can be a number of other reasons for being off from the predicted FG.

- The calibration of your thermometer may be off so that you are mashing at a higher temperature than you think,
- You may be fermenting at a lower temperature than is optimum for the yeast strain used,
- Are you pitching enough yeast?  Check on the yeast starter tab for how much yeast you need (cell count) versus what you are pitching.

Generally, if I was within a couple of points of my final gravity and steady over a number of days (3 to 4) I would consider it completed. Now for most yeasts, I know how long it should take to get to final gravity and plan on a few days more in the fermenting chamber before cold crashing.  If you find a consistent offset, then you can make an adjustment in the formula for fermentability of the wort in your 'options' settings.  Be careful of this and only make the change if you are sure of the results.  Make a note of the defaults so that you can reset it if you need to.
 
Hi. Thanks for the quick reply :)
I made some comments to you suggestions below.
Oginme said:
Carbonated beer would give you an artificially high SG reading as the bubbles will cling to the hydrometer and buoy it up.  If the beer is not carbonated yet, then the presence of naturally dissolved CO2 has a negligible affect on the reading.  You can see this in that your hydrometer will not have gas bubbles attached to it.

You say you are consistently high on FG, but how high are you?  First one ended on 1.022, estimated FG 1,016 - current batch seems to settle around 1.018, estimated 1,014There can be a number of other reasons for being off from the predicted FG.

- The calibration of your thermometer may be off so that you are mashing at a higher temperature than you think, Yup - thermometer used for first batch was 2 degrees too low, so the mash was probably way to warm. On the current batch, the thermometer I used was measuring too high, but I did starch test and it was complete - so on this one I guess I should come home with a highly fermentable mash, or?
- You may be fermenting at a lower temperature than is optimum for the yeast strain used, First batch - yes. Current one should be perfect according to white labs
- Are you pitching enough yeast?  Check on the yeast starter tab for how much yeast you need (cell count) versus what you are pitching. first batch had a nice big starter, but due to time constraints I opted to pitch directly from the liquid pack :(

Generally, if I was within a couple of points of my final gravity and steady over a number of days (3 to 4) I would consider it completed. Now for most yeasts, I know how long it should take to get to final gravity and plan on a few days more in the fermenting chamber before cold crashing.  If you find a consistent offset, then you can make an adjustment in the formula for fermentability of the wort in your 'options' settings.  Be careful of this and only make the change if you are sure of the results.  Make a note of the defaults so that you can reset it if you need to.
Click to expand...

So, I guess I should try a third batch and see how everything turns out if I get all three points right...
 
Just a quick comment on the starch test:  You may read as fully converted, but this has little to do with the fermentability of the wort.  Mashing at higher temperatures will give you a less fermentable wort, as the enzymes will reduce the long chain starches but leave more non-fermentable dextrins in the wort.  The lower mash temperatures will leave the wort with fewer dextrins and more fermentable sugars.
 
Oginme said:
Just a quick comment on the starch test:  You may read as fully converted, but this has little to do with the fermentability of the wort.  Mashing at higher temperatures will give you a less fermentable wort, as the enzymes will reduce the long chain starches but leave more non-fermentable dextrins in the wort.  The lower mash temperatures will leave the wort with fewer dextrins and more fermentable sugars.
Click to expand...
Cool - so if I accidentaly mashed 10% too low, but ended up with full conversion, I should have a quite fermentable wort, and the beer will be a bit drier than planned - but more alcohol :D
Right?

And once again thanks for the feedback :)
 
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