• Yeast
• Culturing

Culturing Yeast

In May 2005 I made my first venture into yeast ranching (at least with agar). I ordered some slants from Brewsters Yeast, these guys have a huge range of yeast and related products and have been very helpful. I started this page while the yeast was in transit.

This is not the first time I have reused yeast. I often save the dregs from a batch, or split some yeast with friends and then usually keep it in its fermented state in the fridge. This method is not useful for long term storage - active cells may remain for weeks and months, however the viability drops off fairly quickly.

Other yeast related wiki pages here include:

• Yeast

• StirPlate

Links

• Brewsters Yeast

• Cagney and Lacey on yeast propagating

• more culturing - untitled

• Yeast Propagation and Maintenance: Principles and Practices an excellent article on culturing

• Freezing yeast

• Wyeast yeast washing page

• Mike Dixon's yeast washing page

• Making a starter

• Starter Primer

• yeast culturing at realbeer

• plant culturing Nothing whatsoever to do with yeast - but their take on the plating process and sanitation is educational.

Agar media

this pic shows a 10g/100ml agar mix which is quite a bit darker than what I use now (see recipe below).

• 100 ml water
• 1.3g agar powder (I used the stuff from an Asian store, $1.00 for 25g).
• 7g DME (Dry Malt Extract)
• pinch of yeast nutrient

I first tried 1.5g of agar and the mix was ok but a bit rubbery for my liking.

From this amount I poured 6 slants and 3 petri dishes. Be patient dissolving everything, I tried a few heat/stir cycles. This mix is sterilized a bit later, when it is hot it is quite gooey.

I poured this much of the hot agar goo into the test tubes. These are polycarbonate and can easily handle the temperatures inside the pressure cooker. The petri dishes are glass.

I fitted the test tubes and three glass petri dishes into the pressure cooker with about 2cm of water. The basket keeps everything off the bottom.

After pulling them out while still hot, laid down to give some surface area (hence the term "slants", cf "deeps"). After some procrastinating I decided to tighten the lids at this stage. I then just put a plastic bowl over all this to keep dust and crap from settling on the slants. Later on I changed my mind (again) and realised that the condensation wasn't going to go anywhere with the lids tight.

The petri dishes went into a plastic container with the lid sitting loosely.

A few days later

• The slants have dried out a little and show no signs of contamination. At this point I closed the lids tightly to stop them drying right out.
• I smeared some yeast from dregs I had in the fridge (1272 and 3068) onto the petri dishes. These yeasts are a couple of generations old, I wanted to practice the plating technique more so than preserving these particular yeasts.

A week later

• The slants I ordered from Brewsters Yeast arrived. The pack was dated 3-May-05 and arrived on the 9th - the weekend probably pushed it out a day or two. Next time I would probably ask to have it sent on a Wednesday or later in the week so it is in transit over the weekend. The tube on the left is antifoam. I thought it might help with some of the blow off I experienced when using the StirPlate.

An innoculation loop I made from 0.7mm stainless steel wire and some scrap brass rod.

• The 1272 yeast I plated - the squiggly line is pretty much all yeast from what I can tell. My plan was to progessively "dilute" the yeast by flaming the loop and picking up from the first squiggle and smearing it into a second quadrant (repeating till I filled in the four quarters). It looks like I didn't pick up yeast from the first "swipe", I would expect to see progressively more sparse yeast colonies. They are not that easy to see through the agar (the petri dish is upside down to prevent moisture dropping onto the yeast).

• The 3068 yeast. On this you can bit of a squiggle in the top left. There are also some white spots dotted around - not sure what these are, I will take a closer look when I open it.

For sealing the petri dishes, Parafilm is the goods! (thanks Sacha). I first used Gladwrap (plastic cling wrap) which worked ok but reduced visibility.

Another 4 days later

This is difficult to see but there is a white "lawn" of yeast of CL-50 on this slant. I attempted two slants each of 3 yeasts. The CL-50 and the CL-400 are fine. The CL-340 just didn't take - no infection, just nothing. I must not have picked up some yeast from the original slant.

So here is answer to what those white spots were - mould. As far as I can tell, I would still be able to lift some clean yeast from the white streaks in the dish. Since this was a trial run it causes no major drama and I am going to toss them out. As an overall comment, the handling of petri dishes seems quite a bit more critical than slants (ie easier to contaminate). They present a much greater surface area, and to streak the 4 quadrants, you keep them open for longer.

The individual white spots across the top of the first photo appear to be yeast colonies from a single yeast cell (or at least just a few).

My most recent addition. This rack has a dust cover and also carefully designed so you can lay it on it's side and the tubes are at the correct angle for slants.

2nd Shot at Plating

I had another go at plating the yeasts that turned out mouldy (see above). This time there are no signs of mould. Technique was similar, just more careful and I didn't flame the loop after each quadrant (thanks for the tip Steve). I also took care to hold the petri dish over the flame source. Looks like it paid off. I have since made slants of these just for posterity.

The farm

3 months later I have a reasonable collection - I am now limited by fridge space but I couldn't possibly keep this many in stubbies.

The yeasts include (not all shown here):

• CL-50
• CL-160
• CL-270
• CL-300
• CL-340
• CL-400
• 1272 US Ale II
• 1318 London Ale III
• 3068 Wheat

Given that I am complete newbie at this, clearly it isn't too hard.

And they are still going strong, I have made beers with a few of these now and in combination with the StirPlate and pressure cooker, my starter making is fairly low stress.

Starter Protocol

The method I use to build up an ale starter for my 23 L batches is below. Essentially I step up like so:

1. 200 ml wort in 250 ml flask. This might take 48 hours to ferment and since you start with such a small amount of yeast, there may be no krausen evident.
2. Tip this into 2 L flask with another 500 ml wort.
3. I then top up in one or two more steps to 2 L.

Stuff I use (Equipment)

1. Yeast culture.
2. DME (about 200 g needed)
3. Water.
4. Yeast nutrient.
5. Scales.
6. Measuring cup, scoop, funnel.
7. 250 ml erlenmeyer (conical) flask.
8. 2 L erlenmeyer flask.
9. Pressure Cooker.
10. Sealable jars suitable for pressure cooker (I scrounge things like pasta sauce jars).
11. Aluminium foil.
12. Stir plate.
13. One or more stir bars.
14. 20 - 25 degree C environment for fermentation.

== Method ==

• coming soon