Yeast Slanting - the low tech wayfrom slanting to pitching

Chris Taylor Melbourne Brewers

Nov 2008

Yeast Propagation

Reasons for yeast slanting– Long term storage– Convenience– Cost effect– Easy to store and transport

Goals of yeast slanting– Minimal yeast mutations– Maximize yeast viability

Yeast Propogation

Reasons against slanting– Requires more time and effort– Greater risk of infections– Yeast will not be the as high quality as the Wyeast or

White labs ( they do extensive quality checks and procedures )

Yeast slants

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 Wort with Gelatin or Agar Agar works will

– Agar Agar can be purchase from most health shops or Asian groceries.

– Inoculation loop Piece on metal that you can heat up with a small loop on

the end.

Preparing slants

Prepare growth medium – Wort (DME etc) @ 1.030

Can include some yeast nutrientAlso possibly a small amount of hopsGelatine or Agar agar

– I prefer agar agar as it is more stable at higher temps

250 ml of wort with about 20g of gelatine Mix in till gelatine is fully dissolved. Or 250ml or wort with about 3.75gms (15gms

per Litre or 1.5% w/v) of Agar Agar

Preparing Slants

Preparing slants

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.– Some people even go to the length of taping up the

lids but I have not found this to be necessary

Preparing Slants

Note try to make sure the caps are losely over the vails so that the stay sterile after you open the autoclave/pot

Preparing Slants

Preparing Slants

Note I always get a bit on condensation in the slants as the cool down and set.

Make sure that the growth medium does not go all the way up to the lid as it may get infected when propogating the yeast.

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.

Cheap and nasty autoclaving (sort of)

Autoclaving (Aside)

I also use this method to sterilise left over wort, and much to my suprise it works very well.

Just make sure you don't overfil the bottles when doing this as they will overflow otherwise during the autoclaving.

I dillute the wort down to 1.030 so that I can pour it straight into the yeast starters when doing the step ups (as it is sterile).

Autoclaving (Aside)

Yeast Culturing

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.– I usually try to hold my breath during this part.

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

or a milky film spread over the surface. If slant shows any signs of infection (mould, wrong

coloured spots etc) it is no good and must be discarded.– The bacteria/wild yeasts/moulds are usually very

obviously different from the cultured yeast. 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 )– It varies depending on the yeast types, I find yeasts

that have very vigorous fermentations such as Yweast 3068 don't store as well as other yeasts.

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]

From Slant to Pitching

Slant to pitching

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.

Slant to pitching

Leave for approx 1-3 day at 22-26C, until some yeast growth is obvious.( A stirplate really helps )

Be patient with this first step, as this is the most vulnerable period for the starter, and as it is starting with a very low cell count, it may take a while before there is any evidence of activity.

Slant to pitching

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

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

When propogating at the higher temperature you really don't want to pitch the resulting fermented wort as it will have probably have some off flavours.

I usually cold crash it about 6hrs before pitching and pour off the original stater wort.

Slant to Pitching

Its also a good idea to taste some of the wort to make sure there are no obvious infection issues at this stage.– Note it will taste pretty awful (sulphury, yeasty, fusels

etc) but should not be medicinal or other obvious bacteria derived flavours.

Slant to pitching

Another school of though is that you should propogate at the temperature you want to pitch.

The advantage here is that you can pitch the yeast while still active (while it is at its peak viability)

The disadvantage is that it will take longer to propagate and you will probably have a lower yeild.

Slant to pitching

– 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 other starter sources, so you really need to use a stir plate.

References

http://www.maltosefalcons.com/tech/MB_Raines_Guide_to_Yeast_Culturing.php

http://hbd.org/brewery/library/YstCult.html