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MooDaddy 02-21-2011 11:46 PM

Specific Gravity questions
 
OK, so I just bottled my first brew yesterday - AHS Double Chocolate Stout extract kit.

According to the kit instructions, the OG should have been 1.056 - mine was 1.068.

The FG should have been 1.012 - mine was 1.024.

Questions:

1. Any explanation for the difference? I did accidentally leave out 1 quart of water I was supposed to add to my wort after cooling. Could that little volume of water make that much difference?

2. It was suggested that I check the calibration on my hydrometer. Can I use regular tap water for that or do I need distilled or reverse osmosis water for that assessment?

3. The calculation of alcohol content is the same with my hydrometer OG and FG readings vs the kit's expected OG and FG readings. That being the case, what is the relative significance of my FG reading being higher than that expected with the kit - denser beer, or does that not make any sense?

nefarious_1_ 02-22-2011 12:46 AM

1. The quart of water you left out has little significance in a 5 gallon batch. More information regarding the brew process is needed in order to understand where the difference could have occurred.

2. Regular tap water should do the trick to check for the calibration, but distilled water would be ideal. Make sure you make up for any temperature differences as well. See what temp. your hydrometer is calibrated to and make the necessary corrections if you're not taking the reading at the proper temperature.

3. Your beer will be denser ie. have more body than the target beer profile. This may or may not be desired, especially if it takes the beer away from the style you're going for.

DCPiet 02-22-2011 03:16 AM

+1 for all nefarious said.

and given that you were going for a stout i'd doubt the extra gravity reading will be a bad thing.

also, are you certain that when you took the 1.024 FG reading that the beer had finished fermenting? i.e. did you take another gravity reading the day after you got the 1.024 and was it still the same?

fact of the matter is that all of us homebrewers here have over/undershot our gravity at some point in our brewing career -- i've personally missed mine by way more than yours was off, and still ended up with a great beer.

rdwhahab

MooDaddy 02-22-2011 03:26 AM

Thanks for the replies.

Yes, I did check the FG about 4 days apart and it was the same.

I checked my hydrometer in tap water just now and it was really dead on.

I'm not terribly worried about the beer not turning out - although maybe I should be - and actually would prefer my stout to be more dense anyway, I was just curious about what possible things in general during the brewing process could lead to SG readings being off, assuming hydrometers are calibrated properly and kit instructions are followed to the letter.

earwig 02-22-2011 03:33 AM

Its very strange that your numbers were off so much. Its nearly impossible to not hit OG on an extract batch since you are already starting with a predetermined amount of fermentable sugars. My guess is that you read the hydrometer wrong :)

VTBrewer 02-22-2011 03:34 AM

In extract brewing, all of the conversion, or most of the conversion, of starch to sugar has been done for you. ie: It comes with the malt extract, which is a known amount of sugar. When mixed with a known amount of water it will come to an OG, as long as it is mixed properly...and it can be really difficult to mix it up well. Steeping grains can add a few points, but certainly not 12 points.

so you probably were much closer to 1.056 if the kit predicted the gravity right. there's really no room for error other than not getting all of it in the pot, not measuring water correctly, not stirring the snot out of it.

If you post the recipes somebody will tell you the predcited OG, but i seldom see them wrong.


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