A yeast slant (A slant is a small tube containing agar or similar growth media and a relatively low number of yeast cells.) is the most common method of storing yeast. Below is a guide to setting up a yeast slant.
The test tubes should come with caps that can withstand temps of 100 deg. C (212 deg. F - but up to/above 121C/250F with pressure cooker) and form a tight seal. You clean & reuse tubes but you will need at least 50 cycling through you're fridge, once your under way.
Used to hold test tubes while they are in the pot/pressure cooker.
Erlenmeyer flasks are used for starter vessels. Be sure to use a with a rubber-stopper and airlock.
Big pot or Pressure cooker
This will be used to sterilize your test tubes and media.
You need to make a growth medium on which your yeast cells will feed. Dried Malt extract is the base and either gelatin (ordinary cooking gelatin from supermarket) or agar-agar (from Asian food stores – comes in sheets). This just sets the malt like a jelly and allows the yeast to live and multiply on top
Don't forget about sanitation so some ethyl alcohol, Starsan, paper towels & cotton balls - I'm going to keep harping about cleanliness so be warned.
Preparing “Blank” Slants
I am assuming that the culturing is from a pure source, like a Wyeast pack.
The First Step is to make up some slants - which you'll use later to grow yeast. (I make between 20-25 with this mix) Sanitize your hands, work area and utensils.
- Boil 1 cup (250 ml) water (in a small saucepan). Remove from heat, add 15 grams of dried malt extract, and stir till dissolved. Put back on the heat and boil for 10 minutes. Remove from heat.
- Add a packet of gelatin into this "wort" and stir until COMPLETELY dissolved.
- Pour this mixture into test-tubes; Fill each about 1/4 full. Keep some empty test tubes for next stage.
- Place a pyrex jug/dish inside a large pot with lid. Place the 1/4 filled test tubes and some empty ones in the pyrex container (if you have a test tube rack which fits in your pot - this can save you some headaches as I couldn't find dishes which fit inside pots).
- Put a couple cm of water in the pot – we don't want water in our jug/dish - we want the steam to sterilize - not the water. Heat until water boils, and keep it boiling for 15 minutes - 15 minutes in steam will kill what you need to.
- I also throw my test tube caps into the container with the test tubes so they sterilize at the same time.
- Turn off the heat, and leave until it cools a little - be careful you now have freshly sterilized test tubes with yeast food. Don't contaminate them. Think Sanitation !!
- Once cool (around) 40 deg.C (104 deg. F) attach the sterile caps, not too tight or else they may get sucked into the test tubes. Tighten caps when cold enough to handle easily. You're finished stage one.
- Lay the test tubes over at an angle of 45 degrees and allow to cool. The slope will give you a slightly larger surface area of yummy yeast food. Don’t fuss about the angle. You are only ever going to grow a little yeast on it… not enough for an army, so a gentle slant is fine. Allow to set for 24 hours, - it will still be a bit wobbly. It’s now ready to be "inoculated" with cells of yeast.
- Ensure the caps are tight and keep these slants at room temp. (20C/68F) for about a week. You want to see if they remained sterile or did they become infected. You will know - they stay shiny. You may see residue of dme and gelatin in the bottom, that’s ok, but if any are infected they will grow stuff on them. It takes a few days for this type of nasty to grow.
- If your slants don’t show any ‘yuk’ then they are fine. Put into fridge and store until you’re ready to use them to culture yeast that you buy or get from a friend.
Inoculating the blank slants with yeast
The procedure will depend on your source of yeast - this is my procedure using Wyeast packs.
Wash your hands thoroughly, sanitize your work area & utensils - lay down some paper towel and lay out your items so you're not rushing to 'unclean' parts of your kitchen.
Have you got your:- test tubes, a long needle (I use a piece of stainless wire flattened on the end), a cotton ball,some ethyl alcohol, and your starter vessel (erlenmeyer flask),and most importantly - one of the empty, previously sterilized capped test tubes.
- Prepare your Wyeast, ready to use in beermaking, i.e. by breaking the inner packet and waiting for it to swell up.
- Shake the Wyeast pack well, and open it using standard procedures. (ensure you sanitize (starsan) the outside of the smakpak and your scissors) Take a tiny bit of the Wyeast solution into your empty test tube. I use a sanitized pipette to suck up the smallest amount, (you could use a funnel if you've a steady hand). Cap the test tube. This small quantity of Yeast will be used to inoculate slants. Pour the rest of the smakpak into your fermenter or grow it up as a starter if that’s your routine.
- Wipe your needle with alcohol-moistened cotton ball to sterilize it. Open the slant to be inoculated. Then open the test tube with the bit of Wyeast solution in it. Dip your needle into the Wyeast, and then *lightly* poke it into the surface of the gelatinous slant. Poke it in several times. Smear it around. Don’t touch the walls of the test tube. At this point, you're only transferring a few cells to begin feeding.
- Withdraw the needle, cap the slant, and cap the Wyeast test tube. You now have an inoculated slant. Repeat the process for each slant you wish to inoculate.
- Now you're disappointed - there is nothing to see... I leave the inoculated slants on the kitchen bench for a week (most of the year that's OK but in summer - I use an esky with 2L ice blocks to keep temp around 19C/66F)– After a few days you'll see yeast begin to coat the top layer. Watch them now as you’re trying to ensure they remained healthy with no bad.
- Within a couple of days you will see a cloudy film on the slant surface, and a few days later it will develop a milky white layer about 1mm thick.
- Sometimes, depending on the strain of yeast, the CO2 produced may begin to push the cap up on the test tube. Just bleed the gas out by loosening & retightening the cap.
- After the week, I use electrical tape to wrap the tops - where the caps meet the test tube wall, and put them into the fridge, where they will keep for xx months. [some say 3 months some say a year?? I tend to agree with a year]
- Don’t forget to label the test tubes with so you know which yeast it is and the date etc.
Some General comments:
- I make about 4-6 test tubes of a yeast type from one source – the number will depend on you. How often will you need ‘that’ yeast? (I re-culture 6 at a time, of the strains that we use most often)
- When you're running low on a strain, simply re-culture the strain by doing the above to new slants, but using an "old" cultured slant as the source. Otherwise the procedure is identical. Re-culturing in this way does not increment the strain generation-number (as the yeast hasn't 'made beer' and replicated themselves enough for mutation to occur [so say the scientists].
- I re-culture from the second last test tube culture of that strain – just in case the last one is ‘unhealthy’ I would have lost that strain from my inventory. E.g. Strain 4 was re-cultured and became 4:01. Then 4:01 was re-cultured and became 4:02 – by keeping the number 4 I always know which strain ‘type’ it was.
Making a starter from a cultured slant
Some folks make a single step starter but I like a small 250ml step then a feeding after 24 hours of yummy wort stolen from the brewery – then I give the Brewer back a flask with 750 ml containing really active yeast.
My 2 step procedure is:-
- Remove slant from fridge – allow it to slowly come up to room temp. Now make a mini starter.
- Remembering to sanitize everything around you and be quick opening your lids - just look around - what could possibly fall into (and contaminate) these vessels - Murphy's law will then prevail, no need to be alarmed - just alert, this is a lot of effort to go down the drain & take a batch of beer with it as well, so slow and clean, OK.
- Mini-wort starter - (1.040 S.G.) 25 grams of dried malt extract in 250 ml water. Boil for 10 minutes in your Erlenmeyer flask -make a lid of aluminium foil snug over the top. The boil process is sterilizing the wort/flask - foil lid allows gas to escape keeping outward pressure. Remove from heat, allow to cool. Now shake the hell out of it – you need to aerate it really well to give the yeast a chance to feed.
- Pour a little wort starter into one inoculated, nicely rich in yeast, slant (I use my sanitized glass pipette you could us a funnel). Swirl it around to loosen yeast. If all the yeast doesn’t comes off the slant surface by simple swirling, use a long needle – swab it with alcohol then gently scrape the slant surface till the yeast comes off (don't worry if some of the gelatin comes with it into your starter – it was all healthy sterilized stuff).
- Pour that into your starter vessel (along with the rest of the mini-wort of course) and attach the airlock. We do this at room temperature unless it's very hot and then we run the air-con - about 24˚C (75˚F) max..
- Next Day. I feed that starter with another 500ml of wort. Either make up a dried malt extract mixture of 500ml water + 50gram dme, boil, cool, shake like crazy etc OR
- If you’re lucky you will have previously stolen wort from the brewmaster (if he’s got extra when taking it out of the boiler into the cubes). I freeze this into 500ml iceblocks – On day 2 of my starter I thaw my iceblock, boil, cool, shake - as above and use that on the second day to feed the mini-starter. This wort from the kettle has all the hops and goodies from grain (the lipids etc) so the yeast really goes wild with that nutrient. But if you don’t have wort – make up the Dried malt extract as above.
- The amount of yeast you extract from a slant will make a robust starter in 36-48 hours; day one you may wonder if you’re done it right – all seems so quiet… by end of day 2 you’ve got bubbling, happy yeast. (by the way we sit ours on homemade stirplates so they are constantly agitated which makes the process very dependable).
- When pitching the yeast from the starter, pour in most of the liquid part, and then swirl the starter vessel to ensure that all yeast cells at the bottom of the vessel are suspended in the remaining liquid; then dump that into fermenter as well. We always see action in the fermenter with 12 - 24 hours.
After a while you get to know the colour and smell of your starters. They smell pretty good actually. And if you can develop an eye for slants that look good - a nice milky layer of yeast, no coloured spots [see the good culture picture], then you're a success. If in doubt - throw it out.
I mentioned getting the wort from the brewmaster (after kettle) but I also watch the mash tun - Once the required amount is in kettle I test the liquid (if any) in the mash tun. If it's a reasonable SG (say high 20's) I continue draining into a jug. I then boil that down for a while in the kitchen to get somewhere near 1.040 and make 500ml iceblocks. While it may not have the hop addition it's still a good pure wort and seems a shame to waste it.
As these iceblocks are thawed and sterilized before use, it an easy process to grab wort and bring to the kitchen without panicking about sanitation while busy on a brewday.
A warning about test tubes - Be aware, they have a life span. I find the caps lose those little 'cardboard' seals. Damned if I can ever find the little circles again! This means they won't seal and can ruin all your work.
That's when it's time to reorganise and put best lids on best tubes and ditch the rest - or if you're like us, move the fridge and watch everything fall, in slow motion, onto the tile floor and break them.
This bulk of this article (all?) originally written by David Draper for the HBD ca. 1995 - Source