Wyeast Smack Pack, Longest Time To Swell

[bindi]

Found a Smack Pack of 1335 British Ale II that was 23 months old a little while ago <_< [it's been moved from fridge to fridge over that time] smacked it and waited 13 days for it to swell tight as a drum, the yeast was great and very strong, it was not a dud that's for sure.
what is the oldest Smack Pack anyone here has used? That made a GOOD beer.

 

[///]

5 years for me. Dave had one which I think was 9 years. All it takes is one cell!

 

[brenjak]

2007 Pilsen lager. 10 months old and smacked three days ago...nothing yet...
Hearterning to hear that all may not be lost yet!

 

[jimi]

Thought I'd raise this thread again, since I've been given a pack that's 13 months old and hasn't done squat for 2 days after smacking.

Just wondering if anyone has ever given up on a pack swelling?

 

[seemax]

I've purchased 5 or so old packs (up to 1yr) from G&G at half price. Only 1 of these swelled after smacking.

In all cases I simply added to my full size starter (1L for ale, 2L+ for lagers), waited til krausen resided, chilled to settle the yeast, poured off wort, swished yeast into suspension and pitched.

They all fermented well and even went on to 2nd and 3rd brews.

Swell schmell ... just pitch it.

 

[hoohaaman]

I have the same experience as seemax.I have only ever ditched a single smack pack,it swelled but the evidence of autolysis was too overwhelming to ignore

 

[drsmurto]

I smacked an 18 month old pack of WY3068 last weekend, 5 days later it was swollen but not bursting like a fresh packet threatens too.

Dumped it into a starter and it took a day to take off but it's now alive and will be stepped up to the appropriate size BEFORE pitching into my beer.

The only time i have ever pitched a smackpack straight into a wort is when it was WY1469 that was a few weeks old. I smacked in at the HBS and within 10 mins i thought i was in trouble. 45 min drive home was fun waiting for a smackpack to go off.....

I always pitch into a starter with something even only a few months old. I see it as an insurance policy.

 

[Dazza_devil]

I smacked an 18 month old pack of WY3068 last weekend, 5 days later it was swollen but not bursting like a fresh packet threatens too.

Dumped it into a starter and it took a day to take off but it's now alive and will be stepped up to the appropriate size BEFORE pitching into my beer.

The only time i have ever pitched a smackpack straight into a wort is when it was WY1469 that was a few weeks old. I smacked in at the HBS and within 10 mins i thought i was in trouble. 45 min drive home was fun waiting for a smackpack to go off.....

I always pitch into a starter with something even only a few months old. I see it as an insurance policy.

Interesting Doc.
I've just been reading up on starter health and from what I understand the first step is very vital in achieving a population of 'healthy ' yeast, as opposed to a good population of unhealthy yeast. Apparently even more-so where old or less viable yeast is used to begin with. From MrMalty, it's suggested to use an initial starter of lesser gravity, even as low as 1.020 to avoid the risk of stressing the yeast.
I'm interested to know your stepping methods with that old 3068 packet, I have some samples which may require some extra attention in this regard. I'm thinking of starting off with around a 20ml feed of 1.020 wort then stepping up to 200ml of 1.030 followed by 2 litres of 1.040.

 

[drsmurto]

Interesting Doc.
I've just been reading up on starter health and from what I understand the first step is very vital in achieving a population of 'healthy ' yeast, as opposed to a good population of unhealthy yeast. Apparently even more-so where old or less viable yeast is used to begin with. From MrMalty, it's suggested to use an initial starter of lesser gravity, even as low as 1.020 to avoid the risk of stressing the yeast.
I'm interested to know your stepping methods with that old 3068 packet, I have some samples which may require some extra attention in this regard. I'm thinking of starting off with around a 20ml feed of 1.020 wort then stepping up to 200ml of 1.030 followed by 2 litres of 1.040.

It was a propagator pack and was pitched into a 500mL starter (~1.040). Put into a ferment fridge set to 22C. Will step up tonight to a 2-3L starter and then smell/taste before deciding if it's ok to pitch.

Never used this yeast so the smell is new to me, definitely getting more banana than clove from the starter.

I also add yeast nutrient to a beer when using the yeast in it's first run. Subsequent pitchings of yeastcake/top cropped samples don't seem to need any help.

Trying to educate myself on all things yeast, one of the things i have been meaning to do is add the yeast nutrient to the starter rather than adding it in the last 5-10 mins of the boil.

Any recommended texts on yeast?

 

[Dazza_devil]

Any recommended texts on yeast?

Here's a bit from 'Handbook of Brewing' edited by Priest and Stewart.

Yeast Pitching and Cell Viability​

Microscopic examination of brewery pitching yeast is as important today as​

it was when first described by Pasteur. It is a rapid way to ensure that there is​

not a major contaminant or viability problem with the yeast. When a sample​

of pitching yeast in water, wort, or beer is examined under the microscope, it​

can be difficult to distinguish a small number of bacteria from the trub and​

other extraneous nonliving material. The trub material, however, is irregular​

in size and outline, and dissolves readily in dilute alkali.​

A trained microbiologist becomes very familiar with the typical appearance​

of the production yeast: the appearance of the cytoplasm, the shape​

of the yeast cells, whether the cells are chain formers, etc. and thus, one​

can sometimes identify the presence of a wild yeast due to the presence of​

cells with unusual shapes or differences in budding or flocculating behavior.​

The use of a viability stain such as methylene blue​

​

​

​

149 gives a good indication​

of the health of the cells. Although there are a number of other​

good stains and techniques available, in experienced hands, methylene​

blue will still quickly identify a viability problem before the yeast is​

pitched. For a review of the various yeast viability and vitality methods​

see Heggart et al.​

​

​

​

150,151​

To accurately determine the health of a culture yeast with a low viability,​

the slide culture technique is the method of choice.​

​

​

​

152 A suitably diluted​

Yeast ​

​

​

​

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2006 by Taylor & Francis Group, LLC​

suspension of yeast is applied to a microscope slide covered with a thin​

layer of nutrient medium. A sterile cover slip is positioned over the yeast​

and the slide is incubated for no longer than 18 h at room temperature.​

The slide is examined at a magnification of 200​

​

​

​

[font="AdvMT_SY"][font="AdvMT_SY"]
[/font][/font]. Cells that give rise to​

microcolonies are viable. Single cells not giving rise to microcolonies are​

scored as dead.​

Yeast pitching is governed by a number of factors, such as wort gravity,​

wort constituents, temperature, degree of wort aeration, and previous​

history of the yeast. Ideally, one wants a minimum lag in order to obtain a​

rapid start to fermentation, which then results in a fast pH drop, and ultimately​

assists in the suppression of bacterial growth. Pitching rates​

employed vary from 5 to 20 million cells per ml, but 10 million cells​

per ml is considered an optimum level by many and results in a lager​

yeast reproducing four to five times. Increasing the pitching rate results in​

fewer doublings, as yeast cells, under given conditions, multiply to a​

maximum number of cells​

​

​

​

/unit volume, regardless of the original pitching​

rate. The pitching rate can be determined by various methods, such as dry​

weight, turbidimetric sensors, hemocytometer, and electronic cell counting.​

More recently, commercially available in-line biomass sensors have been​

introduced that utilize the passive dielectric properties of microbial cells​

and can discriminate between viable and nonviable cells and trub.​

​

​

​

153 The​

amount of yeast growth is limited by a number of factors including​

oxygen supply, nutrient exhaustion, and accumulation of inhibitory metabolic​

products.​

Yeast Collection​

Yeast collection techniques differ between traditional ale top-fermentation​

systems, traditional lager bottom-fermentation systems, and the cylindroconical​

fermentation system. With the traditional ale top fermentation,​

although there are many variations on this system, a single, dual, or​

multistrain yeast system can be employed, and the timing of the skimming​

can be critical to maintain the flocculation characteristics of the strains.​

Traditionally, the first skim or "dirt skim" with the trub present is discarded,​

as is the final skim in most cases. The middle skim is normally kept for​

repitching. With the traditional lager bottom fermentation, the yeast is​

deposited on the floor of the vessel at the end of fermentation. Yeast cropping​

is nonselective and the yeast contains entrained trub. With the​

cylindroconical fermentation vessel, now widely adopted for both ale and​

lager fermentations, the angle at the bottom of the tank allows for effective​

yeast plug removal.​

Today, the use of centrifuges for the removal of yeast and the collection of​

pitching yeast is commonplace. There are a number of advantages, such as​

shorter process time, cost reduction, increased productivity, and reduced​

320 ​

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Handbook of Brewing​

2006 by Taylor & Francis Group, LLC​

shrinkage. Care must be taken to ensure high temperatures (i.e., ​

​

​

​

.208C) are​

not generated during centrifugation and that the design ensures low dissolved​

oxygen pickup and a high throughput. This is usually accomplished​

by use of a self-desludging and low heat-induction unit. Timing control of​

the desludge cycle is important: it allows for a more frequent cycle for​

yeast for the pitching tank and resultant lower solids, or a longer frequency​

for yeast being sent to waste with higher solids and resulting reduced​

product shrink.​

Yeast Storage​

Ideally the yeast is stored in a room that is designed to be easily sanitized,​

contains a plentiful supply of sterile water, a separate filtered air supply​

with positive pressure to prevent the entry of contaminants, and a temperature​

of 0​

​

​

​

8C. Alternatively, insulated tanks in a dehumidified room are​

employed. When open vessels were commonly used, great care had to be​

taken to ensure that sources of contamination were eliminated. Reduction​

of moisture levels to retard mold growth and elimination of difficult to​

clean surfaces and unnecessary equipment and tools from the room are​

useful.​

Yeast is most commonly stored as a slurry at 24​

​

​

​

8C under 6 in. of beer, or​

under a water or 2% potassium dihydrogen phosphate solution. With​

high-gravity brewing, it is important to remember that the ethanol levels​

are significantly higher and that this can affect the viability of the stored​

yeast. As more sophisticated systems have become available, storage tanks​

with external cooling and equipped with low shear stirring devices have​

become popular. Reduction of available oxygen is important during​

storage and minimal yeast surface areas exposed to air is desirable. Low​

dead cell counts and minimum storage time are desirable with the yeast​

being cropped "just-in-time" for repitching if possible.

Bit over my head at the moment some of it but interesting none-the-less.
Bit more just for the hell of it,​

Storage of Cultures​

The most important consideration in the maintenance of a culture collection​

of brewing yeasts is that the stored cultures and their subsequent progeny​

continue to accurately represent the strains originally deposited. The yeast​

preservation method should confer maximum survival and stability and​

be appropriate to the laboratory facilities available. There are many​

methods available to store yeast and bacteria, and a book entitled ​

​

​

​

Maintenance​

of Microorganisms and Cultured Cells ​

​

​

​

A Manual of Laboratory​

Methods​

​

​

​

135 outlines the various methodologies in detail and is a valuable​

resource book. The most common preservation methods currently in use​

are subculture, drying or desiccation, freeze drying, and freezing or​

cryopreservation.​

Subculture, a traditional and popular method, involves the use of two​

vials one for transfer and one for laboratory use, that is, for inoculation​

to scale up the culture for plant use. The cultures are maintained on a​

medium suitable for yeast growth, such as MYGP or PYN,​

​

​

​

136 incubated​

314 ​

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Handbook of Brewing​

2006 by Taylor & Francis Group, LLC​

between 20 and 30​

​

​

​

8C to stationary phase (
72 h), and then stored for up to​

6 months at 14​

​

​

​

8C. At 6 months, the culture is transferred to two fresh​

slopes from the vial reserved exclusively for transfer. Few cultures are​

lost using this method, but the cultures do change over time. Studies​

have shown that in 600 yeast strains studied, after 1025 years of storage,​

46% of the ascosporogenous strains had lost their ability to sporulate and​

50% of the strains that carried amino acid markers had lost some of their​

nutritional markers. In addition, of the 300 brewery strains studied, 25%​

of these strains lost their ability to utilize maltotriose, and 10% showed a​

change in flocculation ability.​

​

​

​

137 In summary, this method is inexpensive​

and versatile, and the slopes are convenient for distribution purposes, but​

the method can lead to unacceptable levels of strain degeneration and is​

not recommended for long-term storage. Another concern is the danger​

of poor technique and cross-contamination, compromising the strain identity​

or purity.​

There are a number of methods that use drying or desiccation. For​

example, silica gel can be used as a desiccant, but this method is generally​

reported to be more successful for genetically marked research strains​

rather than for industrial strains. The damaging effects appear to be very​

strain-specific, and substantial changes in fermentation patterns have been​

observed. Another popular drying method uses squares of filter paper and​

tinned milk as the suspending medium. Again, this method is favored for​

use by culture collection curators because of the ease of mailing cultures​

and is used primarily for genetically marked strains.​

Freeze drying or lyophilization is also a popular technique. It differs​

from desiccation in that water is removed by sublimation from the frozen​

material using a centrifugal dryer. The yeast is sealed under vacuum in a​

glass ampoule. Survival levels tend to be low using this method and​

when 580 strains of ​

​

​

​

Saccharomyces were examined, the mean percentage​

of survival was only 5%. There is also the question as to whether the surviving​

cells represent the original population. Studies have shown little change​

in morphological, physiological, or industrial characteristics, one exception​

being the increased level of RD mutants in some strains of ​

​

​

​

Saccharomyces.​

136,137 ​

​

​

​

Long-term survival is generally satisfactory, and loss of​

viability is usually 1% per year.​

​

​

​

137 The advantages of this method include​

longevity of the freeze-dried culture and easy storage and distribution of​

ampoules. The major disadvantage is the initial diminished activity of the​

culture. In addition, the technique is labor intensive and requires special​

equipment.​

Cryopreservation is the method of choice, as little molecular activity​

takes place at the lower temperatures. For long-term storage, with​

maximum genetic stability, storage at ​

​

​

​

21968C in liquid nitrogen is ideal.​

Storage at ​

​

​

​

220 to 2908C is acceptable but only for shorter storage​

periods. At very low temperatures, there are few reports of genetic instability,​

phenotypic and industrial characteristics are reported to be unchanged,​

Yeast ​

​

​

​

315​

2006 by Taylor & Francis Group, LLC​

yeast plasmids are retained, and the petite mutation is not a problem.​

Of 75 ​

​

​

​

Saccharomyces strains studied, the mean survival rate was 66%.137​

This method clearly yields the highest viability and superior stability,​

but this must be balanced against the disadvantages of using liquid​

nitrogen (cost, handling, delivery) and the inconvenience of culture​

distribution. Mechanical freezers that operate below ​

​

​

​

21308C are now available​

and this eliminates many of the disadvantages associated with the use​

of liquid nitrogen. When this method is employed, it is wise, as a safeguard,​

to keep a duplicate set of the most critical cultures on solid medium at 4​

​

​

​

8C​

in case of mechanical failure or a prolonged interruption of the electrical​

supply.​

Propagation and Scale-Up​

The first yeast propagation plant was developed by Hansen and Kuhle​

and consisted of a steam-sterilizable wort receiver and propagation​

vessel equipped with a supply of sterile air and impeller. The basic principles​

of propagation devised by Hansen in 1890 have changed little.​

​

​

​

138​

The propagation can be batch or semicontinuous. There are usually​

three stainless steel vessels of increasing size equipped with attemperation​

control, sight glasses, and noncontaminating venting systems. They are​

equipped with a clean-in-place (CIP) system and often have in-place​

heat sterilizing and cooling systems for both the equipment and the​

wort. The yeast propagation system is ideally located in a separate​

room from the fermenting area with positive air pressure, as well as​

humidity control and air sterilizing systems, disinfectant mats in doorways​

and limited access by brewing staff.​

During yeast propagation, the brewer wishes to obtain a maximum​

yield of yeast but also wishes to keep the flavor of the beer similar to a​

normal fermentation so that it can be blended into the production​

stream. As a result, the propagation is often carried out at only a slightly​

increased temperature and with intermittent aeration to stimulate yeast​

growth. The propagation of the master culture to the plant fermentation​

scale is a progression of fermentations of increasing size (typically 4​

10​

​

​

​

[font="AdvMT_SY"][font="AdvMT_SY"]
[/font][/font]), until enough yeast is grown to pitch a half size or full commercial​

size brew.​

Wort sterility is normally achieved by boiling for 30 min, or the wort can​

be pasteurized using a plate heat exchanger and passed into a sterile vessel​

and then cooled. Wort gravities range from 10​

​

​

​

8Plato to 168Plato. Depending​

on the yeast, zinc or a commercial yeast food can be added. Aeration is​

important for yeast growth and the wort is aerated using oxygen or sterile​

air and antifoam is added if necessary. Agitation is not normally necessary​

as the aeration process and CO​

​

​

​

2 evolved during active fermentation are sufficient​

to keep the yeast in suspension.​

316 ​

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Handbook of Brewing​

2006 by Taylor & Francis Group, LLC​

The exact details of the yeast propagation will vary whether it is a small​

brewery​

​

​

​

139 or a larger brewery utilizing high-gravity fermentation140 and​

depending on the propagation equipment available. Typically, the initial​

inoculum from the slope​

​

​

​

/plate of fresh yeast goes into 10 ml of sterile​

hopped wort for 24 h at 25​

​

​

​

8C. This is then scaled up to approximately​

100 ml in a 200 ml shake flask, 1000 ml in a 2000 ml shake flask, and 5 l in​

a 10 l Van Laer flask or equivalent using 2448 h increments. The steps​

can be larger and the temperature varied from 12​

​

​

​

8C to 258C with resultant​

longer propagation times at the lower temperature. Scale-up steps are kept​

small at the early stages to ensure good growth. In the yeast propagation​

plant, use can be made of a three-vessel procedure (i.e., 10 hl at​

16​

​

​

​

8C[font="AdvMT_SY"][font="AdvMT_SY"]![/font][/font]30 hl at 148C[font="AdvMT_SY"][font="AdvMT_SY"]![/font][/font]300 hl at 12148C for 45 days), or two vessels​

of 10 and 100 hl are also commonly used with the yeast inoculum being​

transferred from an 18 l Cornelius Spartan vessel. Yields can vary from​

8 to 25 g yeast​

​

​

​

/l depending on growth conditions. A recent paper by Kurz​

et al.​

​

​

​

141 describes a model for yeast propagation in breweries and presents​

the basis for a control strategy aimed at the provision of optimal inoculum​

at the starting time of subsequent beer fermentations.​

Contamination of Cultures​

Various bacteria can contaminate the pure culture pitching yeast (see​

These organisms originate from a number of sources: the​

wort, the yeast inoculum, or unclean equipment. Great care must be taken​

to ensure that there is no contamination during yeast propagation. For a​

detailed review of the bacteria encountered during propagation and beer​

fermentation, and the media required for their isolation, see Priest​

and Campbell.​

​

​

​

142​

Wild yeasts can originate from very diverse sources and, in addition to​

various ​

​

​

​

Saccharomyces strains, include species of the genera Brettanomyces,​

Candida, Debaromyces, Hansenula, Kloeckera, Pichia, Rhodotorula, Torulaspora​

​

​

​

,​

and ​

​

​

​

Zygosaccharomyces143 (see Chapter 16). The potential of the wild​

yeast to cause adverse effects varies with the specific contaminant. If the​

contaminant wild yeast is another culture yeast, the primary concern is​

with rate of fermentation, final attenuation, flocculation, and taste implications.​

If the contaminating yeast is a nonbrewing strain and can compete​

with the culture yeast for the wort constituents, inevitably problems will​

arise as these yeasts can produce a variety of off-flavors and aromas often​

similar to those produced by contaminating bacteria. Some wild yeasts​

can utilize wort dextrins, resulting in an overattenuated beer that lacks​

body. These yeasts are found as both contaminants of fermentation and as​

postfermentation contaminants. In addition, wild yeasts often produce a​

phenolic off-flavor due to the presence of the ​

​

​

​

POF gene.144 However,​

under controlled conditions, such as in the production of a German wheat​

beer or "weiss beer," this phenolic clove-like aroma, produced when the​

Yeast ​

​

​

​

317​

Chapter 16​

​

​

​

​

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2006 by Taylor & Francis Group, LLC​

yeast decarboxylates wort ferulic acid to 4-vinylguaiacol, can be a positive​

attribute of the beer.​

Yeast Washing​

If there is evidence of bacterial contamination, the yeast can be washed to​

purify it. Some breweries incorporate a yeast wash into their process as a​

routine part of the operation, especially if there are concerns over eliminating​

bacteria responsible for the production of apparent total N-nitroso​

compounds (ATNC). There has been much controversy over the use of​

yeast washing and the effects on subsequent fermentations but these​

problems, that is, reduced cell viability, vitality, reduced rate of fermentation,​

changes in flocculation, fining, yeast crop size, and excretion of cell​

components are generally only a problem if yeast washing is carried out​

incorrectly.​

​

​

​

145,146​

Historically, there are three commonly used procedures for washing​

yeast:​

1. ​

​

​

​

Sterile water wash: With the water wash, cold sterile water is​

mixed with the yeast slurry, the yeast is allowed to settle, and​

the supernatant water is discarded. Bacteria and broken cells​

are removed through this process. This can be repeated a​

number of times.​

2. ​

​

​

​

Acid wash: There are a number of acids that can be used. Most​

common are phosphoric, citric, tartaric, or sulfuric. The yeast​

slurry is acidified with diluted acid to a pH of 2.0 and it is​

important that agitation is continuous through the acid addition​

period. The yeast is usually allowed to stand for a maximum​

period of 2 h at a temperature of less than 4​

​

​

​

8C.​

3. ​

​

​

​

Acid/Ammonium persulfate wash: An acidified ammonium persulfate​

treatment has been found to be effective and can yield​

material cost savings. It is recommended that 0.75% (w​

​

​

​

/v)​

ammonium persulfate is added to a diluted yeast slurry (2 parts​

water:1 part yeast) and then the slurry acidified with phosphoric​

acid to pH 2.8.​

​

​

​

145,147,148 This treatment is more effective than acid​

alone at a pH of 2.2. If a pH of 2.0 is employed, a 1-h contact​

time is the maximum.​

Many brewers have a strong preference for a certain regime of yeast​

washing, and a number of factors must be taken into account when choosing​

the method, such as food grade quality of the acid, hazards involved in using​

the acid, and cost. Phosphoric and citric acid offer the advantage of​

being weak acids and yeast pH is more easily controlled, whereas with​

strong acids, such as sulfuric acid, there are special handling procedures​

318 ​

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Handbook of Brewing​

2006 by Taylor & Francis Group, LLC​

required for the operators and a slight overdose will yield excessively low​

pH values.​

Simpson and Hammond​

​

​

​

146 have listed those criteria, which if followed,​

should alleviate many of the problems that are associated with the yeast​

washing process. They include:​

1. Use a food grade acid phosphoric or citric acid are good​

choices.​

2. Wash the yeast as a beer or water slurry.​

3. Chill both the yeast slurry and the acid to less than 4​

​

​

​

8C.​

4. Stir constantly, and slowly while adding the acid to the yeast.​

5. If possible, stir throughout the wash.​

6. Never let the temperature exceed 4​

​

​

​

8C during the wash.​

7. Check the pH of the yeast slurry.​

8. Do not wash for more than 2 h.​

9. Pitch yeast immediately after washing.​

10. Do not wash unhealthy yeast or yeast from fermentations with​

greater than 8% ethanol present (if a wash is unavoidable, use a​

higher pH and/or a shorter contact time).

MrMalty link - http://www.mrmalty.com/starter_faq.htm
​

Still looking around for more on the subject before I build up a 1028 from about 5mm of 6 month old slurry for an EIPA.

​

 

[drsmurto]

Agitation is not normally necessary as the aeration process and CO2 evolved during active fermentation are sufficient to keep the yeast in suspension.

I did read the whole post but this jumped out at me.

What to do with all my stirplates ........

 

[Dazza_devil]

As is the usual, many different sources and many different opinions.
I personally don't see the need for a stirplate but I do agitate, maybe I need an aerator.

I'm downloading a podcast at the moment, el-cheapo dial-up so I have to be patient.

http://thebrewingnetwork.com/shows/Brew-St...-Yeast-Starters

may be helpful.

 

[pk.sax]

I pitched a packet of US-05 into ~1/2L of wort I decanted and chilled off the break in my 1L beer mug. I don't know if it's just that but the CO2 does seem to be keeping the damn thing well stirred. I guess we all need starter flasks with nucleation sites now

Nothing has settled to the bottom of the mug, usually a proportion of yeast always settles when I rehydrate my yeast (with some wort, nutrient, dex and water) in a 1/2 L Pyrex jug. Granted that the mix I used this time is a lot richer, but overnight on the bench and NO yeast settling out. That CO2 keeping things stirred might have some truth to it, at least if the starter container helps it along. I'll post a pic of it in a bit.

 

[jel]

Any recommended texts on yeast?

DrS,

I have this book on order:
Yeast: The Practical Guide to Beer Fermentation
I will let you know when it arrives if you would like to borrow it.

Cheers
Jon

 

[drsmurto]

DrS,

I have this book on order:
Yeast: The Practical Guide to Beer Fermentation
I will let you know when it arrives if you would like to borrow it.

Cheers
Jon

You sir, are a gentleman and a scholar :icon_cheers:

 

[Duff]

I have a number of packs in the fridge which are over 2 years old.

Smacked a 2001 Pils Urquell recently and it took about 2 weeks to swell. When it did swell it was as hard as a fresh pack. Am going to add that to a starter with a fresh pack of 2001 for a large cold pitch in an upcoming pilsener.

 

[MHB]

I did read the whole post but this jumped out at me.

What to do with all my stirplates ........

If you are using an air stone you won't need a stir plate.

MHB

 

[Dazza_devil]

Bit more rant from 'Brewing Yeast Fermentation Performance'

23.1 Introduction​

The purpose of this paper is to offer a brief review of the history of yeast propagation​

for the purpose of brewing beer. By reviewing the literature of historical practices and​

current practices, themes and trends will be discussed. An attempt will be made to​

dispel some of the myths that exist in yeast propagation practices and to offer some​

ideas for the way forward. The concluding remarks will pose the question of how​

far one should optimise yeast propagation, since brewing is a compromise of many​

unit operations and, as such, overoptimisation of one aspect of the process may be​

detrimental to subsequent unit operations.​

Brewing history originated with spontaneous natural fermentations. It was not​

until the work of Emil Hansen, as described by Jones,​

​

​

​

1 that the benefits of using pure​

cultures were understood. To be able to adopt the practice of using pure cultures​

brewers were required to know and understand three key technologies:​

​

​

​

​

strain purification​

​

​

​

​

strain maintenance within a culture collection​

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​

propagation of the selected yeast strain from a few cells to produce sufficient yeast​

for a full-scale fermentation.​

It is perhaps relevant to understand some of the reasons why brewers propagate​

yeast, since at the end of each fermentation cycle brewers harvest the yeast for reuse

in subsequent fermentations. Typically, the reasons brewers give for propagating yeast​

are covered in the following points:​

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to permit the use of pure cultures​

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to accommodate changes in behaviour as a result of cropping practices​

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to prevent deterioration in yeast fermentation performance in subsequent​

fermentations​

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to eliminate the presence of contaminants​

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to reduce the risk of mutations​

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tradition.​

The ​

​

​

​

first three points address the requirements for consistent fermentation performance​

(brewers requirement) and resultant consistent product (consumer​

​

​

​

s​

requirement). The next two points address the safety requirement for the continuation​

of yeast propagation, and the last point is a powerful one in that it has become traditional​

to propagate yeast. Since brewers propagate yeast it is desirable to understand​

the ideal objectives of yeast propagation, most of which are found as answers as to why​

brewers propagate yeast. The principal objective of yeast propagation is to produce​

suf​

​

​

​

ficient yeast for a full-scale production fermenter. The yeast should be produced in​

the shortest possible time, ensuring stress-free growth while meeting plant constraints​

(such as wort availability and brewhouse cycle times). At the end of propagation the​

propagated yeast should have the desired physiological condition to deliver the desired​

fermentation performance. This should be consistent from propagation to propagation.​

The propagated yeast should be free from variants and contaminants.​

23.2 Historical perspective​

Historically, yeast propagation was characterised by small-scale fermentations gradually​

increasing in size until suf​

​

​

​

ficient yeast was produced to pitch a full-scale production​

fermenter. Typically, dilution steps were kept to less than 10-fold increases,​

aeration was minimal and temperatures were matched to those of fermentation. The​

cell productivity of such systems was low (in the order of 70 million cells/ml).​

Thus, the shortcomings of the historical practices can be summarised as follows.​

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​

The cycle required a lot of time.​

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The conversion of nutrients into biomass was inefficient.​

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The resultant yeast produced was of low vitality owing to low oxygen supply.​

23.3 Current perspective​

The changes from historical practices to current practices could not have occurred had​

there not been certain drivers in the industry. As beer production increased so did the​

size of the fermenters, resulting in more stressful fermentations due to increased fermenter​

volumes, resulting in greater wort depths with resultant increased hydrostatic​

pressures. This, in turn, resulted in increased carbon dioxide concentrations, leading to​

increased toxicity effects. The practice of high-gravity fermentation compounded these

issues. At the same time, consumers were becoming more discerning in their taste,​

and thus product and fermentation had to become more consistent. Together, these​

drivers demanded a more vital and healthy yeast capable of dealing with the increased​

fermentaion pressures in a manner that delivered a consistent product to the consumer.​

Brewers were also facing cost pressures, so it was essential that their fermentations​

were consistent to maximise plant utilisation while lowering operating costs.​

One route to achieving the above was to improve yeast propagation, to address the​

long yeast propagation cycle time and low yeast vitality.​

Through the efforts of O​

​

​

​

Connor Cox et al.,2 Lodolo3 and others an understanding​

of the requirements of brewing yeast for oxygen has been developed. In parallel, other​

users of yeast, such as the producers of active dried yeast, had understood the bene​

​

​

​

fits​

of aerobic yeast propagation in terms of both ef​

​

​

​

ficient conversion of carbohydrate​

to biomass and improved vitality of the propagated yeast. Aerobic yeast propagations​

are becoming increasingly common in today​

​

​

​

s brewing industry.48 Indeed, the premise​

in the early days of believing that the best way in which to propagate yeast was by​

batch fermentations of increasing volume appears to be ​

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​

​

flawed. It was only with the​

realisation that the objective of yeast propagation is to grow yeast and the objective of​

fermentation is to ferment with little yeast growth that real progress was made in the​

understanding of yeast propagation. Propagation is about generating biomass and​

fermentation about generating alcohol and ​

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​

​

flavour compounds.​

As stated earlier, current yeast propagation practices are becoming more aerobic in​

nature. Yeast growth follows the standard growth curve characterised by a lag phase​

immediately after inoculation into fresh medium, followed by exponential growth or​

the logarithmic growth phase, and at the exhaustion of a limiting nutrient the stationary​

phase is entered. Logarithmic growth is characterised by rapid, unstressed growth​

that ​

​

​

​

fits an exponential curve; during this stage the yeast is growing as rapidly as possible.​

The stationary phase is characterised by a slow growth rate with little increase in​

biomass, owing to a nutrient (or nutrients) falling below a limiting concentration.​

Biomass productivity per unit time is highest during the logarithmic phase of growth​

and lowest during the stationary phase. Work by Hulse ​

​

​

​

et al.9 confirmed that the optimum​

time to transfer yeast from one stage of propagation to the next is in the late logarithmic​

stage of growth, before the onset of stationary phase. This offers time​

advantages in that the subsequent lag phase of growth is minimised and the propagated​

yeast is not subjected to any nutrient stress. It is essential that this transfer does​

not take place too early in the logarithmic phase of growth, to ensure that the full​

complement of sugar uptake and transport genes has been switched on. Hulse ​

​

​

​

et al.​

demonstrated that large dilution steps in the order of 400-fold are not detrimental​

to the subsequent stage of propagation. In addition, current practices are characterised​

by a gradual stepping-down in temperature until the speci​

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​

fied fermentation​

temperature is reached. This is done to take advantage of the higher growth rates​

obtainable at higher temperatures, thus improving the time ef​

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​

ficiency of the complete​

propagation cycle.​

Research into yeast propagation over the past few years has concentrated on​

increasing the biomass productivity of the systems by focusing on the role of nutrients​

and improving aeration, with some work into alternative systems such as fed-batch​

and continuous systems. In the authors laboratory it has been demonstrated that

increasing the wort gravity used for yeast propagation results in increased biomass​

yields (Fig. 23.1).​

In addition, biomass productivity has increased with improved aeration (Table 23.1).​

A typical production-scale improvement that has been observed is a three- to fourfold​

increase in cell counts at the end of the propagation cycle.​

From these observations it became clear that oxygen does indeed play a crucial role​

in yeast propagation. The biomass yields improved signi​

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​

​

ficantly, with the result that​

the size of the propagation plant could be reduced. Ultimately, the yeast produced​

under these improved conditions is of a higher vitality than that in historical systems​

(data not presented). Amongst the bene​

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​

​

fits claimed7 for fermentations carried out​

with aerobically propagated yeast are a more rapid fermentation, achieving higher​

degrees of attenuation and a higher quality product. However, it should be noted that,​

as a consequence of the Crabtree effect, these propagations are not true aerobic​

propagations in that the yeast is still under fermentative and not aerobic metabolism.​

These claims would allow for the use of decreased pitching rates and/or reduced fermentation​

temperatures while still retaining the same process time. Von Nida​

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7 further​

claimed that the yeast crop produced by means of an aerobic propagation process has​

a lower tendency to autolysis. This will have obvious product bene​

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fits in terms of taste​

and head. A prime drawback of highly aerobic propagation systems is the vast​

amounts of foam formed. Thus, vessels have to have considerable freeboard, making​

them inef​

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​

ficient in terms of space utilisation. The foam produced may also result in a​

loss of desired foam-positive proteins. Thus, it becomes important to understand how​

much oxygen is required and to design a means whereby only that amount is delivered​

to the propagation vessel. The delivery of oxygen to the vessel should be carried out​

in a manner that produces as little foam as possible.​

To summarise current practices compared with historical practices: current practices​

are more aerobic in nature, the dilution steps are much larger, requiring fewer​

stages, and typically the temperatures used are higher. Thus, the current style of yeast​

propagation is more ef​

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​

​

ficient in terms of time and vessel requirements.​

23.4 Future perspectives​

In terms of the future directions of yeast propagation, it is possibly time to extend the​

work on maximising substrate to biomass conversion by ensuring that the conditions are​

such that true aerobic growth occurs with no production of ethanol. Such propagation​

systems have been the standard for producers of dried yeast for some time, and knowledge​

of how yeast ferments after true aerobic growth should be acquired. This could​

lead to the adoption of fed-batch or semi-continuous systems with or without the use of​

novel substrates. However, several questions about such practices need to be answered.​

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Does true aerobically grown yeast retain and display the desired brewing​

characteristics?​

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Can existing beers be flavour-matched with beers produced from true aerobically​

propagated yeast?​

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Should the mode and extent of aeration be continuous or intermittent, and to what​

dissolved oxygen concentration?​

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What are the nutrient and supplementation requirements?​

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What is the optimal temperature to develop the best compromise between growth​

rate, cold shock and the ability to ferment wort to the desired speci​

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fication?​

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Should all fermentations be pitched with freshly propagated yeast?​

By providing answers to the above questions the future direction of yeast propagation​

will be mapped out.​

23.5 Conclusions​

It is relevant to return to the original question, which asked whether further developments​

in yeast propagation will be optimising that stage of the process to the detriment​

of subsequent stages. Indeed, Zepf et al.10 stated that the overriding principle to

be used in the design of yeast propagation plants should be that of producing an optimal​

yeast crop that best meets the subsequent fermentation requirements, and not​

one based on achieving the highest possible yeast counts in the shortest possible time.​

Further optimisation of yeast propagation cannot be done in isolation from the subsequent​

unit operations resulting in the production of high-quality beer. However, it​

does appear that future yeast propagations will be aerobic in nature and that novel​

means of delivering the required amount of oxygen at the correct time will be developed.​

It is less clear whether wort will remain the medium of choice for yeast propagation,​

but it is likely that wort with certain nutrient supplementation will be used for the​

foreseeable future. Process control aspects for temperature, aeration and gas transfer​

will require a great deal of research for the future.

​

I haven't got through it all but there are some useful points there from a quick glance.​

Interesting that perhaps we may be better off stepping up to the next step of a starter before all nutrients have been consumed in the previous step, reducing stress placed on the yeast from running out of food.​

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[drsmurto]

If you are using an air stone you won't need a stir plate.

MHB

No airstone (yet) so my stirplate collection is safe :wub:

 

[thekelsobrewer]

I've just checked a Wyeast 1968 London Ale yeast in the fridge that hasn't been 'smacked' yet appears to have swollen, will this be OK to use?.