How to Slant Yeast

One of the great things about homebrewing beer is the incredible range of yeast available to us. However, it can be expensive to buy each time ($4-10+ per 5 gal batch), and many methods for storing it can be difficult and time consuming. Yeast slanting is an easy way to build up a large yeast bank for long time storage. It doesn't require much equipment, and has very little maintenance compared to other yeast banking methods. In this post, I will explain how I've been doing it.​

Prepared yeast slants

Slanting yeast consists of creating test tubes filled with solid growth medium called slants, which you can use to easily store your yeast for homebrewing beer. The benefits of it over other methods of yeast ranching are:

• Does not require a lot of yeast - Does not affect your starter size.
• Compact - You can store dozens of strains in the size of a shoebox. Everything needed to innoculate a slant is even smaller. Great for wrangling yeast at group brew days!
• Long term storage - 2+ years, indefinite with maintenance.
• Due to the long term storage, it makes a great method for always keeping those specialty yeasts on hand year round.
• Very low maintenance
• Incredibly easy
• Practically non-generational - Yeast has very low growth phase, so almost non-existant chance of mutation.
• Yeast is always 100% clean with no flavor transfer from previous beers

The downsides to it are:

• Does require some equipment - Although all of it is readily available and fairly cheap.
• Requires 1-1.5 weeks lead time to get a pitchable amount of yeast
• It is not viable to keep blends - Since you are dealing with such tiny amounts of yeast, there is no way to slant them or build them up from blends reliably.

We create the slants with a low SG starter wort, and agar agar powder (No, you haven't had one too many homebrews and are seeing double and it's not a typo. It's called agar agar.). The wort provides food for the yeast, while the agar agar solidifies the wort, providing us with a place to grow it. Agar agar is used instead of gelatin, since it sets more firmly than gelatin, has a higher melting point and is harder to digest for bacteria. The name slant comes from the way you allow the test tube to solidify on a slant, which gives you much more surface area to innoculate with yeast. Once made, blank slants can be kept indefinitely at room temperature.

To innoculate the slant with our yeast, all we have to do is swipe our yeast with an innoculation loop, and streak it across our slant. We let that sit for a few days to grow, then fill the tube up with mineral oil, which acts as a protective barrier for the yeast. Innoculated slants must be kept refrigerated, but can keep for 2+ years before they may need to be reslanted, and you can use it for multiple brews in that time, as you only need a single tiny colony of yeast to propogate.

When we want to use a banked yeast strain, we just take our innoculation loop, swipe some yeast out of our slant, then put it in one of our premade mini-starters. From there, we just grow it in stages with increasingly larger starters until we get a pitchable amount of yeast.

Still interested? Let's get to it!

* Note - I am not a professional microbiologist, just a homebrewer interested in yeast. Although I have done quite a bit of research on this, and this method works great for me I am not implying that it is the only or even best method of doing it. If you have any tips, or notice any inaccuracies, please let me know!

Materials Needed

Everything you need to make yeast slants

Slanting yeast doesn't require a lot of materials, and many of them are fairly common household items or can be obtained easily/cheaply.

• Glass Test Tubes w/ Screw Caps - The test tubes must be autoclavable! If you use plastic ones, they may melt when placed in the pressure cooker. You also want them to be fairly large, so you have plenty of surface area for plating the yeast. I personally use 20x150mm Karter Scientific Glass Test Tubes, but anything of sufficient quality and size will work fine.
• Test Tube Rack (optional) - Having a couple test tube racks makes life easier. I have one for storage, and one for holding the tubes in the pressure cooker, so make sure it is autoclavable, like this one.
• Pressure Cooker - We use the pressure cooker to sterilize the slants, starters and wort. It must be large enough to fit your test tubes in, obviously. I personally use a Mirro 22-quart Aluminum Pressure Cooker. Having a big one is nice, because then you can use it to can starters too, which greatly simplifies building up your starters.
• Agar Agar - You can buy fancy lab grade agar agar, however, I just buy cheap Telephone Brand Agar Agar from the local Asian market, which is typically $1 or less for 25g, which is more than enough agar agar for several batches.
• Dry Malt Extract (DME)
• Innoculation Loop (or a paperclip) - You need a long innoculation loop to plate the yeast on the slant. I use one like this, but I make my own, much smaller loops. In a pinch, you could just use a long paperclip.
• Mineral Oil - You just need regular mineral oil, which can be found at your local pharmacy with the constipation aids.
• Glass Measuring Cup/Beaker - You want a glass measuring cup or beaker with a pour spout. The pour spout is important so you can easily pour the medium into the test tubes.
• Electrical Tape - Just plain old electrical tape of whatever color you fancy.
• Masking Tape/Labels - We just need some way of keeping track of what tube is what yeast.
• Gas Stove/Alcohol Lamp - You need to use a clean burning flame source while innoculating slants. I personally use a gas stove, however, if you have an electric stove, you can purchase an alcohol lamp, or make your own. I've even used my propane burner to steal some yeast from a friend while doing a group brew before. DO NOT USE A CANDLE. Candles produce soot, which will contaminate your work and get all over everything.
• Oven Mitts - I like to use silicone oven mitts. You just need something to keep your hands from burning while handling hot test tubes. Test tube holders work too, I just think mitts are easier.
• Cookie Sheet - You need a large flat surface you can lay at an angle. Cookie sheets work great for this.

Preparing Slants

When we prepare the yeast slants, we are going to prepare some mini starters and also sterilize some mineral oil.
​
1. Boil 1L* of water in your measuring cup/beaker.
2. While stirring, slowly pour 70g* DME into the beaker. Make sure it is all dissolved.
3. Pour this into your test tubes, filling them about half way. These will be your initial mini-starters.
4. Pour out enough wort so that you have 500ml* of wort left.
5. While stirring, slowly pour 8g* agar agar into the beaker. Make sure it is all dissolved.
6. Pour this into some other test tubes, filling them about half way. These will be your actual slants.
7. Fill test tubes half-way with mineral oil. You'll need one of these for each slant.

Test tubes ready for the pressure cooker

8. Screw caps on all test tubes so they are somewhat loose. Air will need to escape from them while they are in the pressure cooker.
9. Put all test tubes in rack, into pressure cooker and put the lid on the pressure cooker.
10. Set pressure to 15PSI and begin cooking. Once pressure is reached, set timer for 20 minutes.
11. Once time is up, turn off heat and allow pressure to drop on its own as it cools.
12. Once the pressure has dropped, you can remove the tubes and screw the caps on tight. For the slants give them a good shake, and place them on the cookie sheet, propped up by a pen or something. You want the angle of the cookie sheet to be such that the growth medium covers as much surface area as possible.

Slants angled well on the cookie sheet

13. Now you just need to allow them to cool and stiffen for a few hours.
14. Once cooled, wrap a piece of electrical tape tightly over the cap and tube of the slants, starters and mineral oil tubes, forming a nice tight seal.

Allow the slants and mini starters to sit for at least two weeks prior to first using them (the longer the better), so you can be sure that they are not infected before use. Store the slants, starters and mineral oil at room temperature. There is no benefit to refrigerating them, and it could hide any potential infections.

* You can make the starter wort/agar in whatever quantities or method you want. Just shoot for 1.020-1.030SG for the wort (7g DME per 100ml) and about 1.5g agar per 100ml.

Innoculating Yeast Slants

Now that we've got our slants, lets bank some yeast! The procedure is very simple. It is best to use a fresh, unopened yeast package as your yeast source or a previous slant. This will ensure that your slant is consistent, with only the yeast you want inside. However, you can use a sample from a starter, a bottle of beer, trub, etc. too. Just realize that you run the risk of introducing other micro-organisms, which is especially critical when dealing with such tiny amounts of yeast.

Do all of the below working over your flame source (gas stove on medium, alcohol lamp, etc.). The flame provides a sterile working environment, and will move air up and away from your work.

1. Sanitize the outside of your yeast package.
2. Remove the tape from your blank slant and loosen the cap.
3. Remove the cap from the slant, and flame the lip of the slant for a second to two to sterilize it. If there is some condensation in the slant, dump it out.
4. Put your innoculation loop in your flame source to sterilize it. Make sure to get the whole length of the loop that will be placed in the yeast package or test tube.
5. Take your innoculation loop and insert it into your yeast source. You need only a pin-prick's worth of yeast. You want the yeast to grow from this sample size, not consist of it.

The amount of yeast needed to create a slant

6. Swipe the innoculation loop all over the surface area of the prepared slant. You want to cover as much of the surface as possible.
7. Repeat steps 4-6 once more.
8. Flame the lip of the slant and the cap for a second or two to sterilize them (don't melt your cap!), then recap it. You can finish the following steps outside the flame source.
9. Wrap the cap and tube tightly with electrical tape to provide a nice, tight seal around the cap.
10. Label your yeast slant with masking tape or labels.
11. Let the yeast work for 4-7 days at room temperature. It's good to burp it every day or so, to avoid CO2 buildup. You should now see a bunch of nice, healthy yeast colonies growing on the slant. The time is not super critical. I've left them for up to a month like this with seemingly no issues.
12. Once your yeast has finished growing, we need to add the mineral oil for long term storage. Do the following steps over your flame source. Take one of your sterilized mineral oil tubes and your yeast slant. Remove the tape from both and loosen the caps.
13. Remove the caps and flame the lips of each of the tubes.
14. Pour the mineral oil into the slant, leaving a couple mm, so you don't pour the mineral oil out when flaming the lips.
15. Flame the lip of the tube and the cap for a second or two to sterilize them (don't melt your cap!), then recap it tightly.
16. Remove from the flame source, and wrap the cap and tube tightly with electrical tape to provide a nice, tight seal around the cap.
17. Store in a refrigerator until ready to use.

A finished slant

Using a Yeast Slant

Now that you've got your yeast bank started, let's use one of those yeasts for a beer. It's pretty simple. We'll need to work over our flame source  (gas stove on medium, alcohol lamp, etc.) again here.

1. Remove the tape from your yeast slant and mini starter, and loosen the caps.
2. Remove the caps from the slants, and flame the lips for a second or two to sterilize.
4. Put your innoculation loop in your flame source to sterilize it. Make sure to get the whole length of the loop that will be placed in the tubes.
5. Take your innoculation loop and insert it into your yeast slant and pull a sample of yeast from a single colony. You need only a pin-prick's worth of yeast.
6. Dip your innoculation loop into your mini starter and swirl it around to try and remove all yeast from the loop.
7. Repeat steps 4-6 again.
​8. Flame the lip of the slant and mini starter, and the caps for a second or two to sterilize them (don't melt your caps!), then recap.
​9. Wrap the cap and tube of the slant tightly with electrical tape to provide a nice, tight seal around the cap.
10. Allow the yeast to propagate for 2-3 days. Burp it whenever you walk by it to be safe and avoid CO2 buildup.
11. After the yeast has grown for a few days, dump it into a standard 1.040 SG, prepared 100ml starter*.
12. Allow that starter to grow for another 2-3 days. From here, just grow it to whatever size needed for your beer.

* I like to brew big batches of starters at once, then can them in various sizes of mason jars with my pressure cooker. This makes stepping up starters very simple as you can store them at room temp indefinitely.

Reslanting Yeast/Maintenance

Your yeast should be fine to use, as long as it is still white. Once it starts turning brownish, or after 2 years, you should probably reslant it. All you have to do to reslant yeast is follow the instructions for Innoculating Yeast Slants, except use your old slant as the yeast source. Easy peasy! When I first started doing yeast slants, I actually stored my first yeast bank at room temp, as I seemed to have glossed over the fact that you are supposed to store them in a fridge. During that time, I had used them to make starters just fine, and over a year later, once I realized I was supposed to refrigerate them, I successfully reslanted all of them! This is a very stable method to store yeast.

*Note, this is a guest post from Rivertown Homebrewers member, John Wesorick, and is also posted on his personal homebrew blog.