Lately, especially with Mark’s shaken not stired groupies, there have been a lot of questions about how to tell if your starter is doing its thing. So I tried something tonight on my brew day, and here ya go. It involves some tape and a pen.
The 1728 on the other hand has no sign of high krausen. One might think it was dead if there wasn’t that line showing where the top of the liquid was just after pitching. Notice anything different? Its grown, right? And growth equals good.
I would not expect a volume increase from yeast growth… unless maybe there’s CO2 bubbles displacing some of the liquid? Did you stir the starter to get bubbles out, or could there be bubbles in there? Need more data for this scientific mind.
Now make sure you do everything by the book, and be sure to run some manner of a triangle test, or else your experiences are worthless.
If you manually added 50ml of yeast cells would it increase the volume? Why not if they grow on their own?
Same wort same temp. I think it’s more probable that it’s yeast cells displacing the wort and making it deeper rather than heavy CO2 bubbles. Plus, just after taking the pictures I swirled and pitched. The 1056 foamed up the 1728 did not. Its cell mass. Sorry Dave, if you think it’s wrong the onus is on you to prove it. Right? [emoji12]
The onus is never on me to provide proof of anything. My job is to point out everything that is wrong with your beliefs, thus inferring that in some nondescript way my beliefs, whatever they might be, are far superior to yours.
New theory: Perhaps the density of live yeast cells is less than that of wort. In this case I could accept a slight volume increase. However… I doubt it, based on my superior intellect – no, I mean, based on science. It would probably be very difficult if not impossible to visually detect this volumetric increase. Most likely your tape was marked at a different incline plane. Or you introduced some other unspecified or unknown user error.
In all seriousness… the yeast might be alive. You could try a gravity reading to find out for certain.
Besides, im curious how dormant yeast in a smack pack, pitched into 1200ml of 1.035 wort, produce enough gas to expand the wort that much without any cell growth…
I could take a gravity reading, and will in about 5 days when the beer I pitched them to is done. [emoji12]
Well… maybe 7 days
Fun banter though. You’re enjoying tge devil’s advocate role. And id much rather argue with you than most others.
Anywho, I thought it might be a better method than just posting “is my starter dead” and beleiving what anonymous people post who have not seen your starter.
If you threw me in a vat of beer and then noted the level, then I drank 3 liters of the beer then checked the level, wouldn’t it be the same? My mass would grow by the equivalent of 3 liters of beer but the level would stay the same. After a while though, I would start releasing gas, liquid, and perhaps solid waste. The level might change but its hard to say by how much. The liquid and solid waste shouldn’t effect the level but the gaseous excretions would. The gas that is trapped in the liquid would make it less dense so it would expand (I think) but some gas should also escape, increasing density and decreasing volume. Judging from all the gas I release when I degass my mead, quite a bit of the gas stays in solution, which should increase volume. So I think maybe Jim is onto something, but its the increase in gas, not increase in the volume or mass of yeast, which comes at the expense of it ingesting and using other matter. Nonetheless, that still means fermentation is happening.
What’s interesting is that at least in a full batch of beer, fermentation will reduce the volume of the liquid slightly as CO2 escapes. Unless there was a relatively large increase in temperature, I’d tend toward Dave’s dissolved CO2 hypothesis.
Yeast cells have an SG of 1.0-1.1, i.e. the same as starter wort give or take a few percent.
They grow by consuming sugars. Conservation of mass. The real question is what the final density of the yeast is versus the drop in density of the consumed sugars.
No matter the reason I think the volume expanded due to fermentation and is a valid test. I bet if you put a vessel of wort with no yeast as a control it wouldn’t expand.
Something I learned from Jeff Renner years ago to check if bottles are getting carbonated - the volume of liquid in the bottle will increase with carbonation. Not sure if this is related but I thought I’d throw it out there.
Walking this back just a bit. If you are making a starter with o2 or shaken not stirred, with yeast you dont have a ton of experience with, that may not show an obvious krausen with just 1000-1200ml… you might try splurging on 4" of tape and mark the level just after you pitch. If the level of the starter has gone up 6-12 hours later, it might be an indication that your starter is not dead. Something must have occurred to cause that increase in volume. What else could it reasonably be? Unless your kid dropped crayons in there, or you heated your starter to about 190F, or your flask somehow shrunk.
I cant prove it, but perhaps its an indication of life.
You’re right. My/our point though is that any increase in volume is most likely due to inconspicuous bubbles of CO2, which is a by-product of yeast metabolism; the volume increase is NOT directly from generation of yeast cells themselves, as you can’t make something out of nothing, but rather from their CO2 by-product. That’s my theory anyway.
