Yeast Culturing - the low tech way from slanting to pitching Chris Taylor Melbourne Brewers Nov 2007

Yeast Propagation Reasons for yeast farming – Long term storage – Convenience – Cost effect Goals of yeast farming – Minimal yeast mutations – Maximize yeast viability

Yeast slants

What you need: – Autoclaving equipment (pressure cooker or big pot with weight on lid)‏ – Vials ( must me able to withstand autoclave temperatures > 123ºC)‏ Can be purchased online from medical suppliers. – Growth medium – Inoculation loop Piece on metal that you can heat up with a small loop on the end.

Preparing slants [1/2] Prepare growth medium – Wort (DME Can include some yeast nutrient Also possibly a small amount of hops Gelatine 250 ml of wort with about 20g of gelatine Mix in till gelatine is fully dissolved.

Preparing slants [2/2] Pour growth medium into vials up to about 1/3 volume. Autoclave vials and lids When cool enough place vials on an angle to produce good surface area of exposed growth medium. (Make sure vials are closed tight now that they have been sterilised. – A jigsaw puzzle lid with something under one end is good for this. Leave until set, then store in fridge inside of a zip locked bag.

Autoclaving (or close enough)‏ Requires raising temperature to 123ºC for a period of 15 minutes. Temperature rise above 100 ºC usually achieved by means of pressure (15psi for 123 ºC). Can be achieved with a pot with a weight on the lid ( will probably not get to 123ºC but will be close enough). Sterilisation will also occur at lower temperatures but requires a longer time. Allow 45 minutes for sterilisation to occur in these circumstances.

Yeast Culturing [1/6] Sanitise all working areas prior to starting (does not have to be a large space)‏ Flaming can be used to help keep area free from contaminants. Minimise time that sterile slant is exposed. It is critical for the next part to try and minimise exposure to non-sterile surfaces, air etc.

Yeast Culturing [2/6] ( aside )‏ Make sure air is still in area you are working. – Note bacteria is carried by air and does not crawl. It has to drop down out of the air onto its intended target.

Yeast Culturing [3/6] Sterilise inoculation loop – I just use a naked flame from the stove, and cool it by putting it into a corner of the slant. Open yeast source (wyeast pack etc)‏ Dip inoculation loop into source Open the slant and smear yeast onto the slant surface Close slant lid back up tight.

Yeast Culturing [4/6] Leave at room temperature for approx 1 week. Should by now be able to see a series of white dots spread over the surface. If slant shows any signs of infection (mould, wrong coloured spots etc) it is no good and must be discarded. Label and put back in fridge, ready for propagating Do at least 3 slants of each type ( more if you are intending on distributing to others)‏ Always keep a reference slant to re-culture from.

Yeast Culturing [5/6] Slants should be viable for up to 12 months ( some say as little as 3 months ). Can re-culture from a slant as per above method, except using the slant as the yeast source. – Expect smaller amount of yeast growth when culturing from slant.

Yeast Culturing [6/6]

Slant to pitching [1/4] Very similar to making a starter except that you are starting with a very small amount of yeast. Get 20ml of wort (~1.030) and boils it to sanitise it. ( ~ 1gm DME per 10ml water ). Cool it down, and put in sanitised starter container. Sterilise inoculation loop. Open slant and scrap out yeast with the inoculation loop. – Does not matter if some of the growth medium comes out as well. Leave for approx 1-3 day at 22-26C, until some yeast growth is obvious.( A stirplate really helps )‏

Slant to pitching [2/4] Create 100ml starter as before and pitch contents of original starter into the new one. Leave for approx 1 day at 22-26C. Step up to 1ltr starter and repitch into it. Should consider using a stir-plate at this stage. Step up to 2L (or larger ) stater and repitch. Should consider using a stir-plate at this stage.

Slant to pitching [3/4] Factors to increase yeast yield are: – Ensure oxygenation of starer wort ( make sure you shake it up). – Use yeast nutrient – Use of a stirplate Propagation, not fermentation – Don’t propagate at cool temperatures – Don’t propagate in high gravity worts – Remember, you are making yeast not beer

Slant to pitching [4/4] – Use a stir plate if possible. – One of the disadvantages of propagation from slant is that you will end up with much lower yields then from higher other starter sources, so you really need to use a stir plate.

Yeast Storage Methods Always keep a master stock that can be used to generate a working stock or further master stocks. Master stock should be derived from a known good quality source if possible ( ie Wyeast or White labs pack). Yeast storage (not to confuse with reusing the yeast cake)‏ – Yeast washing – Acid washing – Splitting source yeast Storing yeast samples

Topics for further discussion Pitching rates Estimating yeast cell count

References s_Guide_to_Yeast_Culturing.php