# Yeast growth monitor



## megabyte (19/6/15)

I'm not sure if anyone's tried this before so I thought I'd share and be social 

Background: I think it would be awesome if your stir plate could display how your yeast population is growing. Sure you can tell if fermentation is active from the krausen and tiny bubbles swirling around in your flask, but some of us like to tinker (especially since my wife and I are in the business of building stir plates) and I'd love to be able to visualise the yeast population growth through the lag, active and cleanup stages and see if there's anything useful that can be done with the data that's collected. Maybe if the data is clean enough it could lead to a stir plate that goes "bing" like your microwave when your starter is done :lol:


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Anyhow, today I've been working on a prototype that records the change in reflected light from my test yeast starter. It's too early to know if it's going to work, but when I pitched my yeast (about 1/5th of the safale pack pictured) the sensor picked up a drop in reflected light from about 727 down to 290, so it stands to reason that maybe if the yeast population doubles overnight the light reading will drop significantly further too. It's currently logging to a website and I hope I can post an excel spreadsheet when it's done (successful or not).

If this doesn't work out I might still try shining a laser through the mix or changing the IR sensor to a 600nm sensor since this is more suited to monitoring microorganisms. Comments and suggestions are welcome as always!


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## vykuza (19/6/15)

Sounds excellent Michael! Will change it from a set and hope to hit it at high krausen to knowing when that is actually happening. Keep us updated!


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## droid (19/6/15)

the application is also relevant to fermenters and conditioning vessels


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## luggy (19/6/15)

I'm being the Devils advocate here but how do you know that you have the required cell count, unless your measuring your samples with a haemocytometer over the course of growth


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## Danscraftbeer (19/6/15)

Very cool idea. Just a coupla maybe silly questions. I'm probably off track. Is there any negative affects of light, or lasers on the yeast brew? I made jackets to cover my flasks and fermenters so they brew in darkness. What is the light source? if its surrounding light it has to be constant, or exactly the same for the reading etc. :unsure:


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## Judanero (19/6/15)

If it was to work you might have to chart the measured light vs cell count and see if a correlation can be drawn.

The flocc potential of the varoius strains would also be a pretty big variable, and throw into that yeast viability because light will be affected by dead cells as much as live ones.


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## megabyte (20/6/15)

luggy said:


> I'm being the Devils advocate here but how do you know that you have the required cell count, unless your measuring your samples with a haemocytometer over the course of growth


It won't measure cell count or SG, that's still up to the online calculators and guys in lab coats  For now I just hope to get a "dimensionless" chart of how the cell count is changing.




Danscraftbeer said:


> What is the light source? if its surrounding light it has to be constant, or exactly the same for the reading etc. :unsure:


Good points. The current light source is a 950nm infrared LED which should be far enough away from the blue to UV spectrum that causes light struck beer. Ambient light is still a hurdle and I've kept my bench light turned off throughout the test so far because it skews the measurements about 10-20 units. I'll tackle that problem when I get to it 




Judanero said:


> If it was to work you might have to chart the measured light vs cell count and see if a correlation can be drawn.
> 
> The flocc potential of the varoius strains would also be a pretty big variable, and throw into that yeast viability because light will be affected by dead cells as much as live ones.


Also great points! It's been a while since I've made a starter with a clumpy yeast strain and I forgot how they look when they flocculate on the stirrer. Can't assume our starters are always going to be a smooth homogeneous mix. I'm not sure if yeast viability is an immediate concern, but it will be important if we start trying to estimate viable cell counts.

Thanks for all the feedback. You've raised many points I hadn't considered and also the data that I'm collecting so far is raising more questions too. I wonder if those micro-bubbles of CO2 are also going to complicate things further. Could the levels of dissolved gasses also significantly affect reflectivity? Need to do more study. Here's a chart from just a few hours after pitching - certainly not what I expected, it's becoming more reflective again:
​EDIT: Changed image to JPEG so it would show in my post.​​


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## Danscraftbeer (20/6/15)

That is strange. Might have to team up with some of those dudes in Lab coats.
Excellent if this could work because there is unknown factors when doing starters. The how long?
eg. I use Beersmith and it just has: Starter size and a box to tick if you use a stir plate. How long stired is unknown
and would depend how fast it spins, temperature, and the character of the yeast, and the gravity of the starter wort too.


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## megabyte (20/6/15)

Just an update.. I collected data over night and the trend continued rising (= more reflective wort - the opposite of pitching yeast) which was a little confusing...

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Then I went to see what the starter is looking like and it turns out the stir bar had come off! This is kind of embarrassing for someone that builds stirplates commercially, but in this case I'm using a scrappy stirrer that I cobbled together with parts from the junk pile. Lesson learned.

There is currently only a small amount of krausen on the top so I assume the anaerobic phase is just starting now. I *guess* the stirrer may have stopped working yesterday when the chart stopped falling, and the rising trend could be caused by the yeast falling out of suspension overnight until the last few hours where fermentation is taking off and more yeast is in suspension so it's going sideways again??

I might regroup and try again today with a new yeast starter (and proper stir plate). That way I can also capture the change when I pitch the yeast in the chart as well.


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## NewtownClown (21/6/15)

Michael Burton said:


> Good points. The current light source is a 950nm infrared LED which should be far enough away from the blue to UV spectrum that causes *light struck beer.*


You need hops to cause light strike (skunking) in beer. An unhopped starter is safe


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## megabyte (21/6/15)

NewtownClown said:


> You need hops to cause light strike (skunking) in beer. An unhopped starter is safe


lol good point I think I was having a stupid moment :lol:


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## Danscraftbeer (21/6/15)

My starters are hopped so its still relevant! 
(leftover clear wort from cold crashed trub)

carry on.


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