Purposefully stressing yeast

Oh boy, a question about yeast pitching amount. This thread should be 'interesting'.

I am assuming this will be a moderate gravity ale (e.g., around 1.050). I have pitched a single package of liquid yeast in my moderate gravity ales with great success:

• Fermentation was complete in less than a week
• There were no off flavors (e.g., diacetyl, etc,) in the resulting beers
• I reached my expected final gravity

The yeast vendors will state that a starter is not a requirement for moderate gravity ales and that has been my consistent personal experience over my past 20+ years of brewing.

As to producing a small starter (e.g., 500 ml) there really will not be much yeast propagation in a yeast starter of that size. I personally do not see much benefit here. Maybe a 1 liter on a stir plate will get you the growth you seek?

Cheers!

Edit: I should mention that fermentation success is dependent on other things beyond pitch amount like:

• Proper aeration (oxygenation) of the wort prior to pitching the yeast
• Proper yeast nutrition of the wort
• etc.

 

One of the ways to 'stress' yeast is to "under-pitch". What is your personal definition of "under-pitch"?

In what other ways do you intend to "stress" your yeast?

Cheers!

 

I found this on another homebrew forum and it may be helpful to the OP:

“Pitching rate can affect the amount of esters expressed; ester formation is linked to the rate of growth by the yeast. Many Belgian breweries will underpitch relative to American standards to coax a greater amount of esters out of their already characterful yeasts.”

Cheers!

 

Lower pitching rates and dissolved O2 should stress the yeast. The witbier strain says 72-76% attenuation. So why not lower the OG a bit to allow the yeast to dry the beer out a bit?

My advice if you want to stress yeast for more intense character:

Dry mash rest (148F), low pitching rate, low dissolved O2, medium to high ferment temp (72 to start then allow to rise to 76-78), lower O.G. around 1.045 - 1.048. Also, I like to open ferment, but to each his own.

 

I would use the term "subjective" vs. "variable" in this sentence.

What authority's recommendation do you personally subscribe to? For example, Dr. George Fix published a rule of thumb of 0.75 million cells/ml/P for the case of re-pitching yeast that was used to brew a previous batch of beer. Is this the metric that you personally subscribe to for you freshly manufactured package of White Labs yeast?

For a moderate gravity ale the yeast vendors would not characterize this as an under-pitch condition.

Fermenting just a degree or two warmer is not really stressful to the yeast cells. Yeast actually prefer to grow at temperatures warmer than we typically ferment beer. Warmer temperatures are 'better' for yeast growth but not necessarily for beer production (since off flavors such fusel oils may be produced at higher fermentation temperatures). The bottom line is that slightly fermenting warmer will not stress the yeast cells.

You may want to ferment warmer than you might not otherwise to encouraged the production of esters but there is a balancing act here since I am pretty sure that you do not want to produce fusel oils which will add a harshness aspect to your beer.

The other 'knob' that was suggested by @hoptualBrew was to under-oxygenate your wort. I personally do not feel comfortable suggesting this since I personally do not know how you could 'dial in' a specified value. The rule of thumb for proper amount of oxygen is something like 8-10 ppm. You could decide for this beer to oxygenate to something like 4-5 ppm instead. Do you have a DO (Dissolved Oxygen) meter so you can measure that you met you target here?

Cheers!

 

Fermenting by trying to purposefully stress yeast is a complicated topic and factoring the aspect of "under-pitching" is just a further complication.

At the end of the day this is your beer and you are the head brewer in charge of this batch. You get to choose what you want to do here.

It is a shame that your LHBS did not have the Wyeast yeast strain(s) you made mention of in the OP.

Cheers!

 

Only one way to find out...underpitch one and standard pitch the other (split batch?)

 

I say go for it, Hogue. I can't find it but someone else in here was talking about brewing Hefe and not making a starter for it to "make the yeast work" and really bring out the banana esters. You have a concern of lackluster attenuation. Definitely a risk. But, hey, what's Hitachino Nest's Whit come in at, like 5.5%. A recently dated, well-handled package of yeast fermented at a reasonable range (like I know you do by seeing your posts - you brew a lot!) might give you the results you're seeking. Good experiment I say and I bet it comes out fine for you.

GreenKrusty had a good idea too with the split batch if you really want to get into it!

 

I don't have a whole lot of experience with WLP400, but I (and lots of folks) have experimented with "stressing" hefe strains, which are somewhat similar to WLP400 in that they can make significant esters and phenols. (Most strains do not produce phenols.) So if you really want to stress the yeast, as a starting point perhaps pitch about 1/2 the Mr. Malty rate, and either don't oxygenate at all (beyond your incidental transfer splashing), or if your transfer process doesn't splash, just give it about half your normal shaking. Or, if you normally add pure O2, only add about half (or less) than usual.

BTW, WLP400 is not too terribly different from the Wyeast Belgian Witbier (3944) that your recipe called for. I'm a little surprised that they recommended doing anything special with the WLP400. As always, I recommend taking any LHBS advice with a grain of salt.

 

It's worth trying if it interests you. I have sometimes imagined a brewery that uses just one strain but seeks to maximize varieties od beers as a consequence of yeast handling. Playing with temps, pitching rates, and oxygen amounts suggest a wide range of easy ways you could play with yeast stress. I think it is an interesting idea but proper evaluation would take more patience than I have brought to my own homebrewing, so far.

 

I had fallen into a routine where I would make the recommended starter, use yeast nutrients, and the shot of O2 into the wort, then pitch the yeast at the lower end of its range and let it rise. That works fine for lagers, but makes for too clean British ales.

For an ordinary bitter I have gone back to pitching the yeast pack (no starter), no pure O2, pitch warmer. Someday I might leave out the yeast nutrient.

 

I have used WLP400 a lot. I am also an advocate for stressing out German hefe and Belgian yeasts to help bring out the flavors. However, WLP400 is one Belgian strain that I would not advocate this practice for. It is somewhat of a fussy yeast, and it does throw some sulfur and weird stuff as it is, so I wouldn't want to make things worse by stressing it out a lot. When pitched at normal ale quantities, you will still get lovely pear esters and peppery spice from it, so you don't need to stress it out to get those flavors. Finally, I will also add that I would never advocate pitching or primary fermenting above 70 F for any yeast, including Belgians. If you want to start at 68 F and let the temperature free rise into the 70s, fine. But don't heat above 70 F at pitching on purpose, as that could promote fusels, not to mention it could blow the top off your fermenter. Also note that after the first 2-3 days of active fermentation, you can safely warm up into the 70s to help the yeast keep going and not poop out on you -- that's fine. Just don't pitch it warm or heat it up for the first few days, that's not a great idea IMHO.

'Course, I'm just one person with one set of opinions. You can all do what you like. Experiment to see what you like. I've used this yeast a lot and above are my recommendations based on my own knowledge and experience.

Cheers.

 

@dmtaylor posted: “I will also add that I would never advocate pitching or primary fermenting above 70 F for any yeast, including Belgians.”

I have brewed with the Westmalle yeast strain (Wyeast 3787) a lot. In the past year I used this strain four times to make varying Belgian Ales as a point of example. I regularly permit this strain to exceed 70 degrees F; typically 73 degrees F at the peak of fermentation. This strain produces a glorious combination of esters (fruity flavors) and phenols (spicy flavors) when fermented at these temperatures. I have never experienced any perceptible higher alcohols (fusel oils) in any of my various Belgian Ales brewed in this manner.

I can’t make a blanket statement for all Belgian Ale strains but I can report that the Westmalle yeast strain (Wyeast 3787) produces excellent Belgian Ale when fermented warm (i.e., over 70 degrees F).

Cheers!

 

Brett makes things funkier when its stressed. I have purposely stressed WLP644/OYL200 with very extreme temps (between 45-100F in a room of the house that isn't temp controlled so it stays relatively the same as outside temp) and get much more tropical funkiness out of it when it ferments high (80+). I have kept a session/IPA/DIPA fermenting in these conditions for a few years now and keep a dedicated keg tap for these beers 24-7-365 too. Most sacc strains don't respond well when stressed with high temps though.

 

Earlier I suggested temperature, oxygen, and pitching rate as variables you could play with. Another focus area for coaxing something different out of a yeast strain is altering enzymatic rests in he mash and impacting the yeast through the presence of different metabolic sources. Besides the impact of turbid mashing on the lambic-style beers, the examples that come to mind all relate to hefeweizen yeast and the clove-banana spectrum of flavors you can get from them:

• through a rest that generates ferrulic acid, which some strains will convert to 4-Vinylguaiacol, responsible for clovey character. This one gets mentioned often in various homebrew references
• by mashing in a way that increases the glucose to maltose ratio, which supposedly increases banana character (Apparently fairly well known to brewing chemists and called to my attention in a zymurgy article from about 3-4 years ago).

I could also imagine manipulating other enzymatic rests to influence the chemical environment that east work in, with an impact on yeast-derived flavors. Manipulating protein rests and impacting resulting amino acids concentrations I believe was the subject of speculation by John Palmer on a recent Brew Strong episode, although I do not recall the projected impact he was suggesting it would have on the beer. I suspect that if you delved into the brewing science literature you would find more ideas posed and tested by brewing chemists that for various reasons get less attention in the homebrew circles (one of those reasons being that most of us are not chemists!).