Experimentation (OG - FG question)

Discussion in 'Homebrewing' started by jivemouth, Jun 14, 2012.

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  1. jivemouth

    jivemouth Initiate (0) Jun 14, 2012

    I am experimenting around with modifying an IPA kit from a local homebrewing store. The kit has an OG of 1.069 and an FG of 1.019. I brewed 10 gallons and decided to add some additional DME as well as some corn sugar to boost the alcohol of the batch (first time ever using corn sugar). So in addition to the kits, I added the following:
    • 1.25 lbs of DME
    • 1.3 lbs of corn sugar
    For the record I probably ended up yielding closer to 11 gallons, and my gravity reading off the chilled wort was 1.072 (OG).

    After 1 week of fermentation I added an additional 6oz of Falconer’s Flight Hops (dry hopping), and also an additional ½lb of corn sugar (to trigger another fermentation cycle). I am guesstimating that my final OG would have likely be closer to 1.078 when taking all the additions into account (but I may be wrong).

    I racked ½ of the batch today, taking a sample during the transfer. I didn’t test the FG until after I had racked it, put it under pressure, and started refrigerating it. My actual FG reading was 1.030. This seems high.

    Could adding that amount of DME and corn sugar raise my FG reading by .011? It definitely seemed like the activity had ceased in the carboys. Not only was there no active bubbling for over 7 days, but there was absolutely no visible vertical movement of trub particles either. Any advice? Did I rack that too soon? If so, should I back the pressure off the keg and let it simmer some more in the 70-75 degree range? Any advice for this 2 year vet (relative noob) would be greatly appreciated.
     
    #1 jivemouth, Jun 14, 2012
  2. jokelahoma

    jokelahoma Savant (1,162) May 9, 2004 Missouri

    Hmmm... DME is only partially fermentable, because of the dextrins that are included from whatever malts the manufacturer used to make it. Let's say it averages 80% attenuation, an arbitrary number just for purposes of my little scenario here. That being the case, adding more won't really change the attenuation rate. It'll just add more fermentables and unfermentables. So if your beer at 1.050 was going to drop to 1.010 (again, just hypothetical numbers), and you added more DME to take it to 1.060, you're now only going to drop to 1.012 (still an 80% drop), if all other things remain equal.

    Now let's take the corn sugar. That's close to 100% fermentable. So had you you taken that 1.050 beer and added enough corn sugar to get to 1.060, you'd still drop to 1.010.

    The fact you added both means you added a lot more fermentable sugars, thus raising your OG, but you still added some unfermentables via the DME, which accounts for your higher FG (again, ignoring other variables such as yeast strain, age and viability of the yeast, fermentation temperature, etc., plus the fact that listed FGs with kits are estimates precisely because of those other variables). In other words, an 80% attenuation rate with DME is going to be 80% whether you started at 1.040 or 1.090. Hope that makes sense.

    Also, I'm curious why you added corn sugar when you added dry hops. If anything, any new fermentation would create more CO2, which might scrub a portion of the aroma off your hops, kind of defeating the purpose of dry hopping. Not that it caused any real problems, I'm simply curious as to why you chose to do it that way.
     
    #2 jokelahoma, Jun 14, 2012
  3. jivemouth

    jivemouth Initiate (0) Jun 14, 2012

    Thanks for the response. I figured (from what I have read) that adding some DME would might boost the FG a little... 0.11 seems like a lot though. I did have a taste and it doesn't taste bad (I guess that is the most important part). The initial fermentation was one of the best I have even seen... although that is likely attributable to the starter I made 2 days in advance. Usually I just drop the liquid yeast directly into the carboy. As for adding the corn sugar 1 week in while dry hopping... I hadn't really thought about any possible CO2 scrubbing. I read up on how much more alcohol would be generated from what I had already added in (which was less than may initial estimations) so I figured no harm no foul is I boosted it for a round 2.
     
    #3 jivemouth, Jun 14, 2012
  4. jokelahoma

    jokelahoma Savant (1,162) May 9, 2004 Missouri

    Makes sense on the sugar added after dry hopping. Or sugar added any time yeast is present, for that matter. Like I said, just curious.

    And yeah, while 11 points seems a lot, remember it may not truly be 11 points. You may not have been headed for the estimated FG of 1.019 anyway, but maybe toward 23 or 24. That being the case, a 5 or 6 point increase isn't that out of the question. Remember that vigorous fermentation doesn't necessarily mean high attenuation. It simply means the yeast are really going after the sugars they feel like eating. Adding corn sugar gives them more easily accessible sugars, and it's been theorized that them going after dextrose first can affect their ability to then go after maltose and maltotriose, which could also have contributed to your higher final gravity.
     
    #4 jokelahoma, Jun 14, 2012
  5. jivemouth

    jivemouth Initiate (0) Jun 14, 2012

    Yeah... I can see your point now that you put it that way. Despite the fact that I have been brewing for 2 years, believe it or not I only started actually measuring my OG and FG the past 6 months or so (with the gift of a refractometer for Xmas). I am usually pretty good an judging when the activity has stopped by eyeballing it, but I am trying to be a little more scientific and exact as I brew more and more. Afterall, if I make something I really like, I would at least like to be able to repeat it! :slight_smile: Thanks again for the advice!
     
    #5 jivemouth, Jun 14, 2012
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