Yeast starters and "cell count".

[peebee]

Circumstances created the following unplanned "trial" of yeast starter parameters the other day. Thought I'd share it as it might have some interest to others using (or thinking of using) yeast starters. Skip the next three paragraphs if you can manage without the details.

I'd two brews planned, both recreations of Victorian period "Bitters", fairly high gravity (about 1.060) and fairly well hopped (about 40IBU, EKG). Both used Chevallier barley malt, but one had some 13.5% "pale amber malt" (using one of my "emulations" of old style malting). They were brewed back-to-back, 24 hours apart. The pale amber malt containing one being half the size (22L against 44L). The yeast starters were created from a single WYeast pack, #1187 (Ringwood) being a medium-low attenuating yeast. The pitch rate parameter for the yeast starter calculator being about 0.63-0.65 million cells per millilitre per °P (phew) which I consider to be quite enough for a "British" style beer.

So far, so good. Then it starts going wrong! Not wanting to pour all that oxidised starter wort into my newly created wort, I cool the starters overnight and decant off the excess starter wort. But the decanted wort from the first starter looked cloudier than usual, so it was decanted into a clean and sanitised bottle and chucked back in the fridge.

The larger starter was chucked into the first beer wort. The following day the smaller starter was chucked into the second beer wort, along with the significant quantity of yeast that had settled out of the decanted wort from the first starter. Following?

So the first brew gets the first starter. It will have significantly less than the desired pitch rate. Next day the second brew gets the second starter plus the yeast settled out from the decanted fluid off the first starter. The second brew gets significantly more yeast than intended. The results are (TiltPi plots from the Tilts in each brew):

First brew (44L, under-pitched):

Second brew (22L. over-pitched):

Scales were arranged to cover the same time span for the SG trace (blue). Okay the scales for temperature trace (red) are slightly different but of less relevance as the Tilt's thermometer doesn't control the cooler/heater (they were both set at 20-21C, the saw-tooth patterns above are the result of the different probe positions). The larger fermenter has a Tilt PRO hence the smother traces.

So what can be concluded? Nothing unexpected! Over-pitching cut the start time by almost a half (6-7 hours against twelve hours), and significantly increased the speed of fermentation (three days against five). Though I did manipulate the mashes so the larger batch would ferment down bit more (it's currently down to 1.014½ and I expect it to finish at 1.011-1.012). Manipulating final gravities is so much easier using Chevallier barley (lower diastatic power, or "DP") and low attenuating yeasts (dextrin adverse); sorry, I can't say the same for high attenuating yeasts like US-05 (and most other yeasts). Lucky for me that I think Chevallier barley malt produces significantly pleasanter beer (some might disagree with that).

Make of it what you will!

Note: I thought both worts fermented a bit slower than I'm used to.

 

[The-Engineer-That-Brews]

Many thanks - that is a genuinely interesting post; snd I'd love to try a bit of your beer some time if I can find anything you'd like as a swap.

Though I did manipulate the mashes so the larger batch would ferment down bit more (it's currently down to 1.014½ and I expect it to finish at 1.011-1.012). Manipulating final gravities is so much easier using Chevallier barley (lower diastatic power, or "DP") and low attenuating yeasts (dextrin adverse); sorry, I can't say the same for high attenuating yeasts like US-05 (and most other yeasts). Lucky for me that I think Chevallier barley malt produces significantly pleasanter beer (some might disagree with that).

I'm not sure I followed all of that - could you expand a bit please??
Ta!

 

[The-Engineer-That-Brews]

+1 for using the '½' glyph by the way ;-)

 

[Stu's Brews]

Will be interested to see if there are any discernible differences in flavour or aroma as a result of the different fermentation profiles.

 

[peebee]

Many thanks - that is a genuinely interesting post; snd I'd love to try a bit of your beer some time if I can find anything you'd like as a swap. ...

Have you been talking to that Eric (Jim's, not here)? Has he been saying "speak to that PeeBee, he's good for a free pint!". I'll have a word with him!

Na, I know you mean a bottle swap. Not something I can consider at the moment 'cos I cask all my beers, I've actually not got a lot on (and I want what there is!), and my "odd job" bottling setup is out of commission at this moment. But: Cheers, "watch this space".

I do of course relish an opportunity to spread my "emulated historical malt" ideas about, for which I receive royalties of ... precisely nothing! Though there is the prestige, the fame and (err ... total lack of fortune).

I'm not sure I followed all of that - could you expand a bit please??
Ta!

Not tonight. Dinner to sort out ...

Last time when are started going on about "DP" on this forum I got my nose bloodied. I've got to give it some cautious thought.

 

[peebee]

Will be interested to see if there are any discernible differences in flavour or aroma as a result of the different fermentation profiles.

I'll see, though these are long maturing beers that won't be on tap until December. The real purpose of knocking out the two (apart from only using one Wyeast pack, but that's because I'm a cheapskate) is to see if there's any discernible differences in flavour from using my "emulated historical pale amber malt".

But as you've pointed out, I've also messed with the fermentation making one more fermentable. Result being I probably can't draw conclusions from either tweak.

 

[The-Engineer-That-Brews]

Not tonight. Dinner to sort out ...
Last time when are started going on about "DP" on this forum I got my nose bloodied. I've got to give it some cautious thought.

Think I've worked it out now

 

[Hanglow]

Do you have an estimation how much you pitched into each? You mention 0.63 to 0.65 ml per degree plato, but I'm not sure which beer that relates to, I assume the first? Even in relation to each other. Twice the yeast is only one division, so something like 8x the yeast would be a better comparison, wrt pitching rates

Your first one is obviously a vast underpitch and/or unhealthy yeast, no british beer of that gravity should take five days to crawl to a finish at that temperature imo. The second looks like it should, perhaps its not an overpitch as you say, but a correct pitch?

Most homebrewers tend to underpitch I think, the best way to make good flavour full beers is to pitch lots of healthy, active yeast. It is the choice of yeast that will give you the flavour you want, not under pitching as so many people seem to do.

 

[The-Engineer-That-Brews]

Do you have an estimation how much you pitched into each? You mention 0.63 to 0.65 ml per degree plato, but I'm not sure which beer that relates to, I assume the first? Even in relation to each other. Twice the yeast is only one division, so something like 8x the yeast would be a better comparison, wrt pitching rates

Your first one is obviously a vast underpitch and/or unhealthy yeast, no british beer of that gravity should take five days to crawl to a finish at that temperature imo. The second looks like it should, perhaps its not an overpitch as you say, but a correct pitch?

Most homebrewers tend to underpitch I think, the best way to make good flavour full beers is to pitch lots of healthy, active yeast. It is the choice of yeast that will give you the flavour you want, not under pitching as so many people seem to do.

Just asking, but is there a theory as to why under-pitching should effect the flavour? Simplistically I have assumed that the yeast will just continue a bit longer in its exponential growth phase; and that the pitch rate just effects how quickly the different nutrients and co-factors are metabolised - not the quantity or type of byproducts produced.

 

[Peter Pavlovic]

Wow, I just pitched a packet of Harris beer yeast in my 3.0 kg of lme 7 0.5kg demera sugar and had to use a 'blow off' as the fermentation was so active.

 

[Sadfield]

I'll see, though these are long maturing beers that won't be on tap until December.

But as you've pointed out, I've also messed with the fermentation making one more fermentable.

You could stick some Brettanomyces into it, that'll get the FG down and likely go further to reaching an authentic flavour and aroma.

Just asking, but is there a theory as to why under-pitching should effect the flavour? Simplistically I have assumed that the yeast will just continue a bit longer in its exponential growth phase; and that the pitch rate just effects how quickly the different nutrients and co-factors are metabolised - not the quantity or type of byproducts produced.

Ester formation is linked to yeast growth, as more cell production leads to more of the enzyme that is responsible for alcohol esterification.

I think the problem with under pitching to promote ester production is that it brings with it the risk of more diacetyl, sulphur and fusel production. I'm not sure how much control over it homebrewers have.

 

[peebee]

Do you have an estimation how much you pitched into each? ...

Simple answer ... no!

The exercise came about because I suspected the liquid I decanted off contained a lot of yeast, which it did; about 15mm layer settled overnight in a cooled 1L bottle. At which point the parameters for the calculator (I use a modified version of "Homebrew Dad v1.1") went out the window.

The two starters were built from a single Wyeast #1187 pack. The first was overbuilt and the overbuild (approx 50 billion cells) continued to build the second starter for next day. 1187 is notorious for being late to start as it gets older, and this pack was at its use-by date, so I accept your analysis that the first was under-pitched and the second (which got extra cells from the first) was only pitched about right (not over-pitched).

The first has been a weak ferment. It's still only 1.013½ ('scuse the ½, It's 'cos I use a Tilt PRO and pyknometers; TETB likes them "½" glyphs though!) and I doubt it'll get to 1.013 (1.011 or 1.012 was expected). I'm more used to 2 - 2½ days ferments, even for higher alcohol brews.


I posted the stuff because I know people struggle with their "liquid" yeasts, and hanker after info like this from which they can build their own ideas? I know 'cos I was one of them!

 

[The-Engineer-That-Brews]

Ester formation is linked to yeast growth, as more cell production leads to more of the enzyme that is responsible for alcohol esterification.

Thanks - it was a genuine question and I'll go and try to understand that effect :hat:

 

[Sadfield]

Thanks - it was a genuine question and I'll go and try to understand that effect :hat:

The enzyme is alcohol acetyl transferase (AAT). It was a bit early in the morning for remembering that stuff.

 

[peebee]

Wow, I just pitched a packet of Harris beer yeast in my 3.0 kg of lme 7 0.5kg demera sugar and had to use a 'blow off' as the fermentation was so active.

You'll be seeing the point of all this after a little while. And you wont have to spend 45 years home-brewing before it all starts to click. Unless you have already spent 45 years and you're just a technophobe? The Internet is a great research tool.

 

[peebee]

These beers got casked the other day (30L and two brews in one day - that's a bit too much work: Note to self, don't do it again!). The brews, one pitched with about the right amount of yeast, one accidentally under-pitched, - see above - finished fermenting and had a week to settle. Brew 1 (45L, under-pitched):

Brew 2 (22L, pitched with sufficient yeast):

Same yeast (same pack), very similar recipes (the Simonds Bitter has the addition of Amber Malt). The first trace looks "smoother" only because its a Tilt PRO. The temperature profiles differ slightly and are quite "jagged" because the Tilts aren't responsible for temperature control and aren't calibrated identically - temperature control was set to 20-21°C for fermentation, 16°C for settling. The screen shots (TilpPi Web pages) run different dates, but show about the same time period (the two shots taken about 20 hours apart) so the scale is about the same.

The second profile is about normal, ferment finishing within 3 days. The first required about 5-6 days and there is significant "creep" of SG while settling proceeded.

Final Gravity (prior to casking) was 1.0122 for the first, 1.0181 for the second (pyknometer results). "1.0122" was a fluke (near as damn it, same as Tilt), but the FGs were taken at 18-20°C and the final Tilt temperatures at 14-15°C, and temperature makes a significant difference when measuring SG to four decimal places.

The lower FG for the first was due to lower initial mash temperature for first (purposely). Both Tilts share the same two-point calibration regime (1.000 in 20°C water, and OG of the beer being monitored taken by pyknometer at 20°C).

So, conclusion:

Without the "accident" both starters aimed at a theoretical 0.65 million cells per ml per °Plato, an "ale" pitch level. But the "accident" resulted in the first having significantly less (perhaps only 3/4 of what went into second). The resulting fermentation of the first was certainly more tardy than the second. In this case the difference is unlikely to have a noticeable impact on flavour. But what if the difference was a lot more marked?


More conclusions? Tilt PROs make prettier traces ... na, that's not what this thread is about. Temperature throughout the fermenter will differ, if you think one probe reflects reality, you are kidding yourself ... hmm, still not really on subject. This wasn't a planned experiment, so the fact that I tweaked the firsts mash to make it more fermentable makes it "difficult" to extract more conclusions. Make of it what you will, but if you have "ale" ferments going longer than a week, consider that you may not be working with an adequate yeast starter?

 

[peebee]

... 30L and two brews in one day - that's a bit too much work ...

Me, brew beer? I can't even do simple maths. It was 60L, not 30L (guess that'll keep me going over a few weeks). They'll be on tap for Xmas, but I've not started them as yet.

Some sneaky samples do not indicate any flavour impact of the larger brew's "tardy" fermentation. It wasn't really expected.