maybe my math for figuring % fermentation is off...if im looking for about 75% completion, whats the formula?
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Looking at Mr. Malty and Yeastcalc, you needed 375 Billion cells if that was a 5.25G batch. If you pitched 500B, then that speed would not surprise me. That being the case, take a taste and see whether you need a diacetyl rest at all. You pitched plenty of yeast and sounds like they were quite healthy!
First off....pitching your gallon starter is not really what you did...you made two of the one-half gallon starters which is not the same at all... did you use a stir plate? did you aerate with an aquarium pump? did you use oxygen? forgive me if I do not know your past posts, but many people coming to this forum would not know either unless you specified with more information......IMHO, your fermentation stage is only 61% completed from what you described so why would you want to do the D-rest this early? my math may be wrong and if so I apologize...cheers!!-
So I ran the test- thermowell vs. probe attached to outside of carboy, insulated. The Johnson control probe is in my thermowell, and does not register decimal temp...just whole numbers(52f)My probe on outside of carboy runs decimals(51.5f). so the difference seems to be about 1 to max 1.5f ,as I would have expected.Please pm me the particulars of your test....as a 1.5 degree temp swing (especially with a johnson controller) between actual and ambient, does not seem to follow the test curves plotted by many of the home brewers....especially since you just started a fermentation less than a week ago and my posts are only a couple days old...thank you and cheers!!
While it's true that ambient can be much warmer than actual wort temp, when you place your probe in contact with fermenter and insulate it, you're not measuring ambient - you're within no more than +/- 1 degree of the wort temp.
I used to think the same as your quote above, but I am one who questioned it the more I thought about it...So I performed an experiment placing three thermometers inside my fermentation chamber. T1 was placed in a thermowell at the center of the glass carboy. T2 was taped to the outside of the glass carboy half way up its height and then insulated from the surrounding ambient air in the fermentation chamber. T3 was placed inside the chamber only to read ambient temps. Throughout the fermentation process all probes were within a degree of each other until the yeast activity began to really ramp up. At that time, T1 would follow the increase in yeast activity. T2 would lag behind a couple degrees and T3 would continue to read the ambient which was nearing 1.5 degrees lower than T2 which was 1.5-2 degrees lower than T1 which was reading the interior of the vessel. So at max yeast activity, there was a 3-3.5 degree spread between ambient and internal temps. Now if I want my yeast to ferment a lager at 52F, I want my yeast to ferment at 52F...not 55-55.5F...Ergo, the temp controller is hooked to the probe reading the internal vessel temp, not the other two... YMMV...If you have not performed this test on your own fermentations you may want to give it a try... cheers!!!
not as rigorous as your tests, but when I got my first conical, I tested the actual wort temperature versus the temp read by the probe velcro-ed to the side of the cone at various points during fermentation (i was seeing if it was worth it to get a thermowell), and even at high krausen the dead center of the wort was within a degree (as measured by my 24" SS thermocouple probe and Palmer Wahl reader) of the probe affixed to the side. It was enough to make me forgo the thermowell - I always ferment on the lower side of the range anyway, so even if its 1df off, no biggie.
never tested ambient - figured it was irrelevant.
I screwed up my back at work and they won't let me work for the next couple weeks, so it looks like brewing time! Ground grain today for a pils and an IPA. I'm gonna experiment with a significantly higher sulfate level than I normally use for IPA.