Unconverted Starches and Gravity

This is not my area, but certainly would have thought that starches (whether dissolved or free standing) would affect the SG. That said, to give a higher scientific credibility to the experiment you really should have another hydrometer reading of just distilled water. You know . . . eliminate the temp/calibration error, et al.

Did you taste it? Is that your everyday hydrometer?

 

If i remember right, SG has something to do with density. I could google search real quick but won't. So, I would think that adding almost anything to a liquid will increase its density thus affecting SG. Yes, large solids should affect it much, like rocks in a stream but if you stir up the silt in the same stream the SG will change.

 

This begs a really interesting question: what is the dividing line between something dissolved in a liquid and something suspended? I'm guessing it has something to do with size of the "particulates" and that there is not a clean dividing line. I'm guessing that dissolved quantities are those that show up in a gravity reading, but that suspended objects do not. Just some thoughts off the top of my head.

No surprise to me, though, that dissolved starch affects a gravity reading.

Cheers!

 

Isn’t that dividing line based on whether or not something goes into solution? Which if I remember my chemistry courses correctly when a chemical species dissociates under the slight negative charge of a water molecule?

But then I also remember there is a dissociation constant, so not all of the substance necessarily dissolves, sooooo I guess yeah there is no clean dividing line, especially because malt has so many different things in it.

I think the reason wort is so easily measurable by density is because starches, once converted to sugars would have a very high dissociation constant, but complex starches would have a lower constant, even though a portion will still dissociate ?

Thinking out loud here. This is interesting though!

 

I had no doubt.

 

What was the reading an hour or so later once everything settled?

 

Very interesting. I'm not a scientist, but I'm guessing that what you're trying to show is that anything soluble; complex carbs, sugars, proteins, will affect the gravity. However, things that are insoluble: fats/oils, insoluble fiber, etc. will not? I agree with this hypothesis.
Been a long time since I took any sort of chemistry or biology class, so feel free to correct me and spell all this out.

 

So basically, what you're saying is to not worry so much about the given range of attenuation of a particular yeast strain, but focus more on the overall fermentability of the wort?

 

On the matter of whether or not conversion is complete, it is something to consider. However, an iodide test is easy, quick, and cheap.
How does one measure or even estimate the amount of unconverted starches or soluble proteins in a wort?

 

Particles in suspension will alter hydrometer readings. Soil scientists exploit this principle when they use specially calibrated hydrometers to evaluate soil particle size distribution.

Vikeman's measurement probably included both soluble and insoluble starch particle. He filter ot the large particles but the small ones take longer to filter out. No one in beer talks about suspended solids, presumably because the impacts of suspended grain particles is very low, especially relative to the impact of the soluble sugars that are concentrated in the wort. We are typically avoiding having a lot of suspended solids.

 

SG is just a measure of weight in a given volume, soluble things will affect density. Particulate matter typically will also affect gravity since the weight of that particle is often different than the weight of the same volume of water.

There is definitely a difference between suspended and dissolved. Suspended is still a solid, but whose buoyancy keeps it from fully sinking or floating, particle size matters. If it sinks or floats it's not truly suspended. Solubility tells you the saturation point of a given compound in a given fluid, or what percent is in solution and what percent is in its native form, either a solid, another liquid, or a gas.

With a hydrometer it will matter what liquid it is in contact with since this is what is displaced. If more solids are either sinking or floating around the hydrometer then the gravity reading will be changing. At low concentrations the difference would be very hard to notice. If solids are sticking to the hydrometer, it is adding to the weight of the instrument itself.

 

Did you check your starch sample with a refractometer?