Violating the Laws of Biochemistry and Alcohol

[whovous]

Brewing is simple. Is that why it makes me feel like a simpleton?

Tonight, I brewed Biermuncher's Centennial Blonde. Basically, I tried to downsize his original recipe to 2.5 gallons, with a single change. I used Gigayeast Vermont (Conan). The idea, stolen from Braufessor, is to harvest the resulting yeast for future IPAs. Yeast harvesting is brand new to me, but that's a question for another day.

So, 60 minutes at 152F, then ten minutes at 170F, when it finally occurred to me to take a pre-boil gravity reading.

Initially, I got a refractometer brix reading of 9.9, which translates to 1.0396 SG. This was with very warm wort, so I took a little more wort in a syringe and ran it under cold water for awhile. This time, the refractometer read 9.6 brix, or 1.0384. Given that Beersmith estimated my post-boil OG at 1.042, this seemed like a surprisingly high pre-boil number. I figured that since my efficiency numbers have been up and down, then tonight was on the efficiency side.

So, I did a 60 minute boil, then used the chill plate to get down to the upper 60s, and then dropped a pump in a bucket of ice water to get the wort down to about 60F. I moved the wort to the fermenter, oxygenated for 60 seconds, and then pitched a full package of Vermont Yeast in my 2.5 gallon fermenter.

It was right after I pitched the yeast that it dawned on me that I had not checked my post-boil gravity. I did not agitate the fermenter after pitching, so I figured that simply putting my syringe below the surface would get me wort and not yeast.

With the wort temp at about 60F, I got a post-boil gravity reading of 8 brix, or 1.0318. This seemed impossibly low, so I syringed again, and this time I got 7 brix.

I am sure there is a simple explanation for all of this.

What is it?

 

[didinho]

did you measure gravity with a densimeter too?

 

[whovous]

You mean a hydrometer? No.

 

[Qhrumphf]

All grain or extract? I'm assuming all-grain. Did you stir prior to collecting your preboil sample?

Cheap refractometers can experience a pretty wide spread of numbers.

 

[whovous]

All grain. I have a continuously recirculating mash, so additional stirring should not be necessary.

I bought the refractometer because my hydrometer was giving me inaccurate readings. Water was 1.004, for example.

I just measured with a new hydrometer and got 1.033, FWIW. I still don't think the preboil reading makes any sense.

 

[Qhrumphf]

Well, issue has to be with the readings somehow. You're not going to have a higher preboil gravity than post boil gravity, period. So readings on one end are innacurate. If that level of efficiency indicated by the preboil is abnormally high for you, then yes, I'd suspect those to be the erroneous ones. Or there's something else wrong here. I'm hoping this is a stupid question, but you didn't add water at any point between the readings did you? Could be an issue with your refractometer, like I said. Properly calibrated? Are you accounting for the different refraction of wort?

What were the actual volumes for each measurement?

Also not sure how much the gravity would have dropped in 9ish hours, but gravity now may not be the best indicator.

 

[whovous]

I did not add water. I do not understand "accounting for different refraction of wort."

The preboil reading seemed high for a beer where the recipe calls for a final ABV of 4.1%.

 

[Warthaug]

Is your refractometer calibrated (i.e. reads '0' if water is used)? Alternatively, the yeast would be packaged in a low-gravity solution; you may have simply drawn off a top-layer of the low-gravity yeast liquid.

Once fermentation is complete you can use a combination of the refractometer reading and a hydrometer reading to estimate the OG.

B

 

[UndeadFred]

For a super yeast starter 1.033 to 1.045 or so is perfectly fine, so you are good. One of the annoying things I learned about my refractometer is that you really want to either use a pipet and let the sample cool in the bulb for a minute or two before putting on the slide, or you want to get it onto the slide IMMEDIATELY.. as fast as possible. What happens if you pick up a drop on a spoon and dawdle getting the slide closed is that a significant but unpredictable amount of water evaporates off when the water is above about 140F (when you start to see evaporation or "steam")... [causing an incorrect high gravity reading that is much lower once the wort is cool, exactly what you saw]

So pipets are kinda the cheap insurance though I find taking a quick sample with the spoon is the lazy way. I had my readings bounce all over the place until I figured that out after a year or two (with pipets) of pretty solid readings.

You also need to look into the "wort correction factor" calculator from Brewer's Friend. I was lucky and my particular unit was close enough to one that I initially didn't know better, and once I did I realized it was close to a correction factor of one.

But you should be fine with it when you sort out these two issues. Oh, when recalibrating the refractometer--- you HAVE TO use DISTILLED water, RO even at single digit PPMs wil read a small amount of Brix on the unit. You should recalibrate about every 3 brews, or at least that is what I found on mine.

 

[jabba11]

a single drop on a cool refractometer is gonna cool pretty dang quick fwiw. I mean really quick. your spreading a droplet across a cool wide surface. Also I have a cheap one. It doesn't "vary widely". Truth be told I don't really know how the thing works but it seems like a simple enough device. My guess..you read it wrong or wrote it down wrong. I work in the air industry. Number one cause of a crash. Pilot error.

 

[Qhrumphf]

I did not add water. I do not understand "accounting for different refraction of wort."

The preboil reading seemed high for a beer where the recipe calls for a final ABV of 4.1%.

You also need to look into the "wort correction factor" calculator from Brewer's Friend. I was lucky and my particular unit was close enough to one that I initially didn't know better, and once I did I realized it was close to a correction factor of one.

This is what I was referring to. Refractometers are designed to read pure sucrose solutions, not wort. Maltose and other wort sugars (only part sucrose) refract similarly to pure sucrose, but not identically. Result is that a corrective factor is needed, which will vary from refractometer to refractometer. Several data points of different worts at different gravities will get you very close to an average corrective factor (but technically every wort will refract differently as the sugar content of wort is so varied). Measure a calibrated hydrometer vs a calibrated refractometer and compare the difference. Dividing the Brix/Plato by 1.04 is a common one but isn't accurate for everyone. My factor is also very close to 1 so I can just use as is. I think Kai's writeup on it put his closer to multiplying by 1.04 instead of dividing.

 

[whovous]

I followed the instructions to calibrate the refractometer when I bought it. This is the second or third brew since calibration. I tried tap water last night and it read 0 or very close to it.

Operator error is most definitely a part of my skillset. That said, when the first test seemed on the high side to me (170F wort to syringe to glass plate) I tested a second time (170F wort to syringe, held syringe under cold running water, then to glass plate). The second reading was not all that far from the first. This seems to reduce the likelihood of operator error, but then again, we are only rarely smart enough to figure out when we are being idiots, aren't we?

 

[whovous]

As I think about this further, the measurements taken immediately after oxygenating and pitching the liquid yeast have got to be be suspect. I got back to back brix readings of 8 and 7. I think I must have differing amounts of yeast in each sample. I don't know what else could create that large of a swing in under a minute. My wort was well mixed beforehand, but the yeast was not mixed at all, just dumped on top.

Also, I think Qhrumphf makes a good point on the measurement this AM. Fermentation was not massive, but it was definitely starting by the time I took the measurement of 1.033, so last night's lower numbers must be simply wrong. Now, rationalizing this AMs number with the pre-boil numbers is still a bit tough, but the gaps are at least a little easier to believe.

BTW, what does "North London is Ours" mean?

 

[whovous]

Googled "North London is Ours." I was going to guess it was somehow a reference to the brewery in Tottenham Hale. I got the Tottenham part right. Back to Woolwich for me, I guess.

 

[Qhrumphf]

Googled "North London is Ours." I was going to guess it was somehow a reference to the brewery in Tottenham Hale. I got the Tottenham part right. Back to Woolwich for me, I guess.

Yep. That's the gist.