Confused

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Confused

Post by tourer » Mon Jan 08, 2018 10:31 pm

I'm confused, If using a dried yeast you only add to cooled sterilised water to activate why would adding the yeast to a malt based starter "supposedly" kill of 50%? of the yeast cells? If i culture a 1.5 litre starter (i use the runnings from the last brew) surely my healthy yeast count would far exceed the original 50% loss and the yeast is ready to start work on the wort.

brewzone

Re: Confused

Post by brewzone » Mon Jan 08, 2018 10:36 pm

It can rupture the cell walls but I get good results using Nottingham added direct to wort up to 1.052 og without a problem.

McMullan

Re: Confused

Post by McMullan » Mon Jan 08, 2018 11:13 pm

You will find about 50% are dead before doing anything, due to the drying process. The cells are dehydrated and require water to rehydrate. Sugary wort isn't as good for rehydrating the cells and, strain dependent, might promote additional osmotic shock. Follow the manufacturer's instructions, which might differ from the supplier's :?

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Re: Confused

Post by orlando » Tue Jan 09, 2018 6:24 pm

McMullan is right. When cell walls are rehydrating they are not as good at managing what passes through their membranes and wort is not what the cell walls need at this point. Only use water, I don't think sterile water is vital but preboiled and cooled tap water is fine.
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Re: Confused

Post by Kev888 » Tue Jan 09, 2018 8:14 pm

Yes, as mentioned above dehydrating and re-hydrating are quite challenging for the yeast; some cells die in the process. Asking them to cope with wort before they're hydrated (and so able to work properly) adds further to their problems, and so more cells die than with water alone.

But it is all relative, and it is common for manufacturers to officially permit both re-hydrating and dry-pitching in their data sheets. Hydrating is best for the yeast, dry pitching is best for convenience (and may also be safer for the inexperienced). The choice depends on which takes priority.

I prefer to hydrate since it isn't a big chore and seems like best practice. But on those occasions I've pitched dry (many over the years) the extra losses don't seem greatly significant assuming a good, healthy amount is being pitched to begin with.
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Re: Confused

Post by MTW » Tue Jan 09, 2018 11:26 pm

I concur with all the cell wall stuff and documented benefits of re-hydration. It's a while since I read the 'Yeast' book, but I wonder if anyone can address the OP's remark about a starter more than making up for any cell loss due to pitching into wort, from a scientific point of view. Whichever model of calculation you want to believe for the number of cells produced in a 1.5L starter, 50% of an 11g sachet would still (the calculators say...) yield far more cells than a full 11g going into the batch rehydrated, and that's assuming that 100% of the rehydrated cells get going OK.

I do wonder what must happen to the remaining dry-pitched-into-wort-cells, if the shock was bad enough to kill up to 50% of them outright! :shock: But then many folk don't rehydrate, and I taste their beers and they're still superb!

For my penny's worth, there's no reason I'm aware of why I'd bother making up a starter with dry yeast, unless ...and I did this once, successfully... I'm trying to acclimatise a re-pitch due to go into an already partly fermented wort that needs help, and I don't have anything else to hand. For one thing, the dry yeast is said to have little or no oxygen requirement in the main batch, below something like 1.060 IIRC. If I'm bothering to make a starter, it's usually because there's a liquid strain that I'd prefer to use over the dry ones available; the main advantages of going dry (little oxygen requirement and ease of use) are therefore lost, for me. The common advice that I've seen is that if you do need more cells from dry yeast, just buy another pack.
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Re: Confused

Post by tourer » Tue Jan 09, 2018 11:28 pm

OK i get that. What if i hydrate then make a large starter as i dont like the wort sitting there waiting for the yeast to work. That may seem like an unnecessary extra effort but i'm not too bothered. It may be that the lag time is no different but thats just me.
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Re: Confused

Post by Kev888 » Wed Jan 10, 2018 12:37 am

The lag time is rarely a problem if the temperature and pitching rate are correct (and of course if things were well disinfected); if this seems excessive then maybe something fundamental needs addressing. If all is well but you just wanted to speed things up, you could perhaps help get the hydrated yeast into gear slightly earlier by adding a little wort 'shortly' before pitching, but I'm not sure how well this would work with dried hydrated yeast - for me, its more of a technique to bump liquid starters.

TBH I'm not a yeast expert like McMullan and others, but personally I wouldn't bother with a vastly over-inoculated dry-yeast starter - especially as an alternative to simply rehydrating properly. There would be little creation of nice new healthy cells, and key advantages of the dry yeast could be lost in the process.

If I really needed to grow up dried yeast, then I'd use a more typical, smaller inoculation rate - to at least reap the benefits of fresh cell creation - and then treat as liquid yeast when it came to aeration of the main brew. But I'd probably need to be using free/saved wort or cheap sugary media for the starter, rather than bought extract, to make this much of a saving over simply buying extra dried yeast.
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Re: Confused

Post by McMullan » Wed Jan 10, 2018 8:54 am

A lag phase (several to <24 hours) is perfectly normal. The cells are actively adapting to the fresh wort conditions, synthesising proteins (enzymes), modifying the cell wall, etc. It is a good indicator you haven't over or under pitched; no or short lag phase and extended lag phase, respectively. I think if you're going to go through the 'rigmarole' of making a yeast starter, you would be rewarded no end by using a liquid yeast, which imparts more character, in terms of flavour and aroma, than dried yeast.

One of the conveniences of using dried yeast is the wort does not need to be aerated. The cells have been preconditioned and don't usually require O2. (I'd aerate an imperial strength wort.) If you pitch a starter into wort, the wort does need to be aerated, to provide required O2. This seems to catch out quite a few home brewers when they first progress from dried to liquid yeast.

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Re: Confused

Post by Jim » Wed Jan 10, 2018 10:44 am

When using dried yeast I hydrate soon after I switch the boiler off. Once the cooled wort starts flowing from my cfc I add small amounts to the hydrated yeast bit by bit before finally adding the whole lot to the bulk wort.

I can't remember where I picked that up from, but it supposedly gets the yeast used to the wort gradually (especially from the point of view of temperature which is difficult to match exactly between yeast mixture and bulk wort).
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brewzone

Re: Confused

Post by brewzone » Wed Jan 10, 2018 11:41 am

Jim, that's genius at work.

Will be doing that from now on !

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Re: Confused

Post by jaroporter » Wed Jan 10, 2018 1:00 pm

i'd just echo McMullan's last comment. the only benefit i can think of with dried yeast is convenience with not needing to aerate the wort or make a starter. as soon as you cross that barrier you may as well be using liquid yeast.

for what it's worth i do think you get improved performance out of dried yeast once you've got it 'wet' - a second generation nottingham ferment is night and day better than the first for me - so there may be that argument for using a starter with it, but then you kinda lose the point of using dried yeast IMO
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McMullan

Re: Confused

Post by McMullan » Wed Jan 10, 2018 2:48 pm

Quite a few observe that subsequent generations perform better. I think it has more to do with questionable quality of the initial yeast pitched. I grow up fresh cultures in a lab for most of my fermentations. Occasionally, when time and needs permit, I'll harvest and repitch into another batch of wort. I don't see any change in performance. Freshly rehydrated dried yeast, especially, look pretty desperate under a microscope. So do 'fresh' liquid yeasts sometimes, to be honest.

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Re: Confused

Post by Rookie » Wed Jan 10, 2018 5:26 pm

I've mostly used dry yeast for quite a few years now and I don't remember ever having rehydrated the yeast or bothered with aeration other than slight splashing when transferring from the kettle to the carboy.
I've always had fermentation start in less than 24 hours, including a couple of batches of imperial pilsner that I did last year for an article I just submitted to Zymurgy.
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Re: Confused

Post by jaroporter » Wed Jan 10, 2018 7:17 pm

McMullan wrote:
Wed Jan 10, 2018 2:48 pm
Quite a few observe that subsequent generations perform better. I think it has more to do with questionable quality of the initial yeast pitched.
that's my implication really. clearly the drying process is stressful and that's before you take into account everything the pack goes through to get to the point of pitching.
i'm probably at risk of getting off topic (and i'm trying not to let personal preferences overshadow too much!) but the difference in fermentation between a healthy pitch and a (even rehydrated) dry pitch is a telling indicator, for me at least.
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