Chris Taylor Melbourne Brewers Mar 2009 Yeast Startergrowing and using yeast
Yeast Starters Why? What? Process Dry yeast
Why? Healthy yeast = happy beer :) If you get the first step wrong you are setting yourselves up for failure before you even start. Benefits most probably save money you will have fresh viable yeast you will learn about yeast behaviour before pitching it
Why? Increasing yeast cell count for: Higher gravity beers Larger batches Under pitching consequences Long time for fermentation to start (lag time) Greater risk of infection Formation of more yeast defects (esters etc) risk of incomplete fermentation In short you may get away with it for some of the more robust yeast strains, but results are much less predictable.
Why? Ensuring yeast is healthy before pitching Old yeast with low viability 'Cheap' out of date liquid yeast packets Saved yeast slurries left for too long (> 3 weeks)
Why not? More time More complex Greater risk of infection But is usually detectable Alternatives Buy more yeast Re using yeast
What Growing yeast, not making beer! Need to provide ideal growth conditions Not the same as for ideal beer production Same for lager and ale yeasts Wort ~ 1.020 to 1.040 Temp ~ 26C Constant agitation Driving off CO2 helps yeast production Nutrients (especially oxygen)
Yeast phases Lag Phase Wort acclimatization Oxygen is extremely important. used by yeast for synthesis of sterols and fatty acids necessary for growth factors. Without oxygen growth will be very limited. Log Phase The log phase is a time of exponential growth of the yeast culture. The preparation the yeast made during the lag phase allows rapid multiplication of cells and consumption of sugar. Many of the significant aromatic and flavor compounds are by-products of cell growth and are produced during the log phase.
Yeast phases Stationary Phase Where the yeast population reaches maximum density and the remaining sugars are consumed. When the yeast have consumed all of the sugar, flocculation begins.
Equipment Vessel to grow yeast in Must be sanitised of course! Plastic container (eg Juice bottle) Jar Emerlyser flask Can sanitise with heat (heat on stove) Easy to use with a stirplate No need for airlock Makes yeast work harder. Reduced oxygen has big impact on yeast growth. Foil over the top is fine while CO2 is being produced. Not suitable after CO2 production has ceased.
Equipment Stirplate Really need emerlyser flask Can greatly accelerate yeast growth Drives off CO2 Keeps yeast in suspension Allows more air/yeast contact, potentially allowing more oxygen access. You need one if you use start from small amounts of yeast Slants or plates, culturing from bottle dregs, etc
Ingredients – Starter Wort Dry malt extract 1gm per 10 ml for ~ 1.030 SG Should be boiled up to ensure it is sanitised Liquid malt extract Can get at HBS and sometimes low quality types at supermarket Saved wort Must be sterile to store at room temp Can be frozen, but needs to sanitised after defrosting
Ingredients – Starter Wort Sugar? Not recommend, does not contain any FAN or other required nutrients May be used with nutrients but still better to go with malt. No hops (or as low as possible) Reduces yeast growth
Ingredients - Yeast Packaged liquid yeast Yeast from a commercial bottle Not really necessary these days with Wyeast and Whitelabs range, exception being Coopers. Slant or some other stored yeast Dry yeast? Generally not worth it, and yeast is designed to be pitched as is (does not even require much aeration) Only real difference is the amount of yeast you start with. The more yeast the better!
Ingredients - Yeast Quality of starting yeast is important Bad parents will result in more likelihood of demented children. There are ways to reculture suspect yeast, but that is a whole new topic. Try to avoid “stressed” and over-used yeast. Each propagation risks more mutations Yeast used in high gravity brewing is not recommended (its well and truly passed its best)
Ingredients - Yeast Try to get yeast closest to the “source” of known good yeast in following preference: Liquid yeast packet from yeast supplier Slant or stored yeast from above Yeast collected from Krausen Yeast from secondary Yeast from primary Yeast from bottle Yeast just found lying around the shed floor :p ( this is commonly known as an infection)
Ingredients - Others Yeast nutrient FAN (Nitrogen) Generally available from the malt in the starter wort Old yeast boiled up I just use cheap bakers yeast Specialised nutrient Contains minerals such as Zinc and Magnesium, yeast hulls, diammonium phosphate etc Will give the best overall results Oxygen!!! Is critical to yeast growth
Process – Estimating required yeast How much yeast do I need? Pitching rates Experience!!! << This is the most important factor Mr Malty pitching calculator Generally accepted as 0.75 million cells per ml per º plato wort strength ( 1 plato ~ 1.004 ) Need to double for lagers. (just use the yeast calculator if you have access to it) This is a guideline only, and is often disputed!! You really need to be familiar with the yeast strain to know how to use it properly. No substitute for experience
Process – Estimating required yeast Ale yeast, 1.055 OG and 23 litres 0.75mil x 23,000 x 55/4 Last part is conversion from 1.055 into º plato 237 billon cells Lager yeast, 1.068 OG, 23 litres 0.75mil x 23,000 x 68/4 x 2 587 billon cells!! Note both are considerably more than available from a single liquid yeast packet.( ~ 100 billion, if it is fresh )
Why you want even more yeast Fast ferment Simple test to see how attenuative your wort actually is. Ie what is the finish point? Add small amount of wort to some of the propagated yeast Make sure it is at least 2-3 times what is required Ferment in a warm environment Insurance against: Incomplete fermentation Note it does not have to be the same strain! Can use more robust and attenuative yeasts even. This is a whole new topic. Fermentation defects remediation Acetaldehyde Diacetyl etc
Process – Making yeast Finally lets get on with it: Most important factor is how much yeast your are starting with High count start > 100 billion cells << Easy Starter Liquid yeast package Save yeast slurry Dry yeast ... only if you really really need to Low yeast count << Harder Starter Slants Bottles Small amounts kept under sanitised water
Making yeast - Easy Starter Prepare wort 1gm of DME per 10ml water Add nutrient Boil Do it in the emerlyser flask if you have one with some foil mostly over the top will sanitise it at the same time. Cool down to pitching temp Make sure propagating container is sanitised!
Making yeast - Easy Starer Prepare yeast Bring it up to room temperature No need to “smack” wyeast packs, but no harm in doing so. The nutrient in the smack packs will aid yeast growth. If using saved yeast pour off non yeast liquid
Making Yeast – Easy Starter Pitch yeast into starter wort If not using a stirplate you need to aerate well. Oxygen is one of the greatest limiting factors of yeast growth. Shaking up a container with a lid on it is a great way to get it aerated. Don't put an airlock on the container ... we want the oxygen to be able to get in! Add yeast to container
Grow yeast Place in warm environment ( > 22 C < 28 C is best ) Don't let the temp drop below 20C if possible Try to avoid large fluctuations As always there is an alternative way Grow yeast at temp you want to pitch Growth rate will probably be a lot lower (especially at lager temps), but yeast will be more readily adapted to the fermentation environment Also can pitch starter wort without fear off off flavours I do not recommend this method Making yeast – Easy starer
Making yeast – Easy starer If not stirplating agitate often (the more the better) Drives of CO2 and give more access for yeast to oxygen. Not making beer! You don't really want to see a normal fermentation taking place with huge krausen etc Does not matter if there is no krausen at all Can tell it is working by the changing colour of the starer wort. The lighter it is getting the more yeast.
Making yeast – Easy starer Approximate growth rates for 100 billion cell starter 1ltr starter = ~ 172 billion cells 2ltr starter = ~ 230 billion cells 4ltr starter = ~ 305 billion cells 1ltr, then step up to 4ltr = ~ 400 billion cells Step up means to add additional 3 ltrs to make total of 4 ltrs Make sure wort additions are boiled then cooled down as per previous steps. Growth phase should be completed in approx 24hrs.
Making yeast – Easy starter After growth phase is complete cool down to 4C to ensure rapid flocculation occurs Ideally better to slowly cool down if possible. May need to leave up to 24hrs achieve this step Pour of starter wort Note you should taste some of the starter wort and make sure there are no infection issues Also gives you a good idea of the types of esters etc the yeast is capable of producing. Yeast is now ready to pitch!!
Making yeast – Harder starter Starting with very small yeast counts has the following additional challenges: Much higher risk of infection for first step due to very low yeast cell counts Many smaller steps required to reach final pitchable quantities Starter yield will probably be much lower
Making Yeast – Harder Starter First step Start with no more than 20ml of starter. Pay particular attention to sanitation for this step. Grow at same temp as easy starter. May take up 3 days for any real noticeable activity Should wait until sample is cloudy and clear evidence of yeast growth before starting subsequent steps
Making Yeast – Harder Starter Step up in quantities of no more than 10x current starer size (x6 is even better) Allow about 24hrs for each subsequent step Will see more signs of fermentation as original yeast begins to ferment over time A stirplate is required if you need to do this often (eg starting from slants etc).
Making Yeast - Stirplate Magnetic stirbars are much easier to work with Faster stir will result in better growth, but does not have to vortex Dont leave it on the stirplate for excessive time it will eventually have a negative effect on the yeast 24hrs is usually adequate
Alternative Methods Softdrink bottle method Put yeast and wort in a sqeezable softdrink bottle. Periodically squeeze CO2 out of bottle. Let air back in. Shake up again. The more you do it the faster it will grow. Reportedly this method can result in rapid yeast growth in very short timeframes
How much yeast do I have? Measure it! Yeast cell count Need microscope amongst other things. Sounds really painful, but some brewers do it. Really need some training to do this properly.
How much yeast do I have? Approximation technique Pour off ~ 80 ml into 100ml measuring flask when just completed. Put into fridge and let flocculate out. Wait for it to really compress down (takes about 2 day) Not volume of compressed yeast (it should look much whiter by now) Yeast will contain appox 4.5 billion cells per ml Can now calculate appox amount in yeast starter.
Dry Yeast Preparation of dry yeast You need to hydrate in water before pitching! Yeast that is not hydrated can not protect itself against absorption of excessive sugars results in signifigant loss of cells, and those that survive are the worse off for the experience. Use pre-boiled water, cooled down to around 25C About 1 cup per 8gms of yeast Let it sit in water for about 30min prior to pitching.
Other References John Palmer – How to Brew Brewing Network – Brew Strong podcast Mr Malty – yeast pitch calculator Wyeast website Whitelabs website http://braukaiser.com/wiki/index.php?title=Growing_Yeast_from_a_Plate