Yeast handling and Storage
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Yeast handling and Storage |
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Sooner or later as a brewer you will drift around to the idea of using liquid yeast. But when you check it out, you will soon see these things are not cheap. About $11.00 to $15.00 a packet. As soon as they discover the cost, many people will forget the idea then and there. This is a pity, because liquid yeasts will improve your beer dramatically.
But how do other brewers manage to use these? Are they all fabulously wealthy? No. There are secrets to getting these costs right down. In our case, we culture yeast stored under sterile water in test tubes. There are other methods which are covered in other articles, but in this one we will cover storing your own yeast and culturing it as needed. You can click on any of the pictures to see a larger, more detailed one.
Graham says: "I have used every method out there to store my yeast. Each has its disadvantages but probably the biggest one I have found is the short storage period you can keep your yeast. Even freezing it doesn't guarantee longevity. The other thing I hated was no matter what method I used, I had this agonising wait restarting the yeast up, wonder if it was contaminated, was it healthy, will it be alright?
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What I wanted was simple. I wanted to store all the yeast cultures I would ever need (about twenty at the moment). That way I could brew whatever style that turned me on. But I also wanted certainty that the culture would fire up clean. And because I have soooo many cultures, I wanted the longest period of time between re-cultures. For me, sterile water storage was the answer." Its really quite simple. Yeast itself is actually quite a tough little bugger. The organism is quite adapted to going long periods without the right environment (food, temp etc). In fact yeast has the great ability to basically just "go to sleep". If you transfer vigorous healthy young cells and put them in an environment containing absolutely nothing for them (in this case sterile water), they will just go dormant. If you store these in a fridge they will live, or sleep for years. Note the word sterile. This is not sanitised, it is sterile. If you allow other organisms in the test tube, there is every likelihood that they will feed on your yeast. I can hear the cries from a lot of you now. This sounds too complicated. But the truth is, it's easier than you think. I will go through what you need and how to do it. Its not all that difficult, but there is a lot to get through. You don't need a degree to do this, just attention to detail. |
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| All said and done this is what it is about. Here's my own yeast station I pulled out of the fridge. Note the one in the hand. The water is clear and that there is only a very small amount of white yeast in the bottom of the test tube. Each test tube has a different type of yeast in it. |
Firstly, before we explain how to store the yeast, lets see how easy it is to start it up for brewing, beginning at the point where you have your yeast stored in a test tube of sterile water.
About 7 days before you want to brew, using sterile techniques (to be explained later) you shake the tube to re-suspend the yeast. You then take a tiny bit of liquid from the test tube (resealing it properly immediately) and quickly streak an agar plate in a petri-dish and put the test tube back in the fridge.
In two days you'll see lots of little colonies all growing happily. When they get to a good size, you lift two good match heads full and put them into a 300 ml starter (`8-10 g dry malt per 100 ml of water, boiled or preferably pressure cooked). Give it lots of aeration.
Graham says: "I put it in a plastic soft drink bottle and every six hours, or whenever I'm passing, I squeeze out the air in the bottle a couple of times and let fresh air in and give it a good shake."
Within 24 hours you should have activity such as cloudiness, lightening of the colour and a small surface build-up of froth. Then you add more sterile starter wort to double the size of the starter. Repeat doubling as often as you like.
So its:
· Saturday- streak plate
· Monday- check plate, re-streak if necessary or, if really going, seed a 300 ml starter
· Tuesday - transfer to 300 ml starter if not done already
· Wednesday - 600 ml starter and to the size you need.
When to the right size cool down in a fridge for the brew session.
Now, the only difference between what we have just described and preparing yeast for storage is that 1) the yeast for the initial streaking will come from an original source such as a liquid yeast pack, or an active starter made from some bottle dregs, and 2) when you lift the colonies, instead of placing them into starter wort, you place them into your storage vial of sterile water.
So let's get on with it step by step. Here is a list of equipment you will need.
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Everyone should have an Autoclave. You will be surprised how often these things pop up round the place, second hand stores and auctions. Presure cookers will work fine, but autoclaves are easier to use. | |
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Yeast propagation gear. This picture shows the basic gear you need. Test tube with stopper, petre-dish and two wire loops made out of stainless steel. | |
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Of all the ingredients and materials I had to get this was the hardest (if you live outside the big cities). These are packets of agar. They are a natural compound that act the same as jelly, but unlike gelantine, stay so at room temperature. They are found in oriental food shops. these two packets will last me about 5 years. |
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Here's my gear set up for a yeast transfer to the plate. The red thing is a gas lighter, the yeast is in the test tube in the cup, I wrap my plates in glad wrap for extra protection, and the burner is a simple camping burner. Note you dont need to be in a lab. A very clean bench will work. The bench was cleaned with bleach. | |
Not too bad is it?
Now it's time to cover how to prepare the plates and test tubes-vials. First we have to prepare some agar plates in petri-dishes. This is dead easy. You first need some agar, commonly available from Asian supermarkets. Beg borrow steal, but get some agar, its cheap as chips. You also need some dried malt extract (DME).
Graham uses an autoclave set to a working pressure of 15 psi. It will build up on the gauge to about 250 kPa and a temp of about 135c. "Oh, my pressure cooker doesn't have all those fancy dials" We hear you cry. Don't worry, just put water in the bottom and check the instructions to get roughly the right weight. Two key points, you need it to run for about half an hour at that hissing stage to sterilise your stuff.
Steve says: "I use an ordinary pressure cooker running at "vigorous hiss" for 20-30 min and this has worked for me just fine."
Preparing agar plates: In microbiological circles this is called growth media. For each 100ml of media you mix 2g of agar powder and 5g of DME. Other nutrients can be used but we do not find that necessary and won't go into it here. You boil the solution to dissolve the agar and then pour a thin layer into your clean (but not necessarily sterile at this stage) dishes. You can get four to five plates from 100 ml of media. You then place these carefully in your pressure cooker on some kind of rack (we'll leave that up to your creativity). Position lids so they are 3/4 on to allow them to be easily pushed over the dish later.
That's it, blast away. Let it go for about a half an hour, then let it sit for another half and hour. Open lid carefully while still hot (do we have to mention the bleedin' obvious about safety?) and with the lid slightly ajar, push the lids on the dishes with a clean thing-a-me-bob (long bladed knife run through a gas flame, maybe), put the lid back on the cooker and let it cool. When it's cool, you'll have nice sterile agar plates.
Graham finds it a real pain measuring, mixing and pouring agar solution into petri-dishes. He says: "There is a far easier way. 1) Put a level teaspoon of DME in each dish. 2) Get a tiny wheeny teaspoon and put in the dried agar (its actually 0.5 gram), an amount the size of a small to medium pea 3) Pour in hot water just to cover the bottom of the plate (~20 ml or 1 tblspn) and give a gentle stir. 4) Don't worry, if it doesn't mix properly, it does so in the pressure cooker. 5) pressure cook and cool as described above".
If reculturing mother cultures an option is to add a little bit of an antibiotic tablet to each dish as well. And the cost? How does two cents per plate sound? Just affordable?
The test tubes/vials are similar. But what sort of water should we use to store yeast in? Answer: Ordinary tap water! If it's drinkable, use it. For sterile water storage, distilled water is a big no-no. You need some of the dissolved salts in the water to maintain equilibrium with the yeast. So to prepare, just boil a couple of times in your kettle. Put about an inch of boiled tap water in the bottom of the tube, lid on top ready to seal, and again let her rip in the pressure cooker. Seal test tubes/vial as hot as you can bear to touch the thing. Graham says: "I use these neat rubber stoppers for test tubes. They allow the pressure to escape, (without blowing off), but as it cools the stoppers are "sucked in". Thus my test tubes seal themselves. They are ready to use. Put aluminium foil over the top of each and store in the fridge".
Now there are basic principles that should ensure you don't get infections. It's all common sense stuff. You've probably seen news, science reports, documentaries, where there are white coats working with petri-dishes. There they are, looking at the dishes in the light, trying to look holier than thou, etc. But most of all when you see them lift the lid to take a sample they are quick.
1. Be quick. Since plates only cost 2 cents a go, you should practice your speed until you can do this with confidence.
Now you will also see that the white coats have these fancy cabinets to work in. They are designed to minimise infection by isolating you as much as possible from the sample. So how do you approximate this at home?
2. Wipe all the surfaces you work on with disinfectant.
3. You have seen the movies, really wash your hands.
These cabinets also have fans etc so you can't get infected from the air and your breath. So..
4. Do as much work in the morning, the air is generally as still as it gets (less air currents)
5. Hold you breathe when the lids are off (seriously), and try not to breathe on it. This is another reason to be quick!
Finally there are stock standard things you do to reduce the chances of infection. You all have seen it some time. A little flame they stick stuff, like wire loops into. The burner on a gas stove will do nicely, or if you don't have one, any kind of small portable propane burner will do. Raid your camping box!
6. Flame loop immediately before each use
7. Flame test tube opening when you open and when you are ready to seal.
Finally these guys will work in a small area to reduce the chances of infection. You should do the same. Everything should be close to each other but organised. Also it should be close to the flame.
8. Flame causes an updraft. And that draft should be sterile, because it has been through the flame, right? Working within the flame updraft, well above it so as not to kill your yeast, means it's pretty sterile and difficult for anything to settle on an exposed surface (e.g. your opened dish or yeast sample on the loop) because of the air current.
9. Avoid actually touching anything that could get in touch with the yeast. Only hold tops of lids and sides of petri-dishes.
That's about it. If you have a gas stove, working right next to the stove will do it. Graham says: "Believe it (or not) I do all my culturing in my work room. Its very dusty, dirty, and not clean. Yet I can culture with confidence, I have a small special table I pull out, clean and disinfect. Provided I follow good culturing practices, perfect every time."
Steve says: "Be aware that spores and things can get into your plates over the few days of growth. Find a good big tupperware (or similar) container and sanitise the inside. Stack your plates in there. Leave the lid on loosely or separated by some paper towel to allow gas exchange. A lovely little incubation cabinet!"
We have written the above for the Aussie craft brewer with an emphasis on making it as practical as possible. Another detailed article, not by an Aussie, but with some nice little animated graphics, can be found by clicking here.
One of the biggest issues is where to try and source some of the more specialist items. We'll leave you with some suggestions.
1. If you work in a lab of some sort you don't need to read any further. You should be able to obtain all the equipment needed through lab "throw aways".
2. Try and make friends with someone who works in a lab ;-)
3. Look up labs in your phone book (pathology labs would be the best option) and just call and ask if they have any surplus equipment (especially tubes, stoppers and petri-dishes - even ask about inoculating loops) or whether they can sell you some of the equipment. There are laboratory supply companies out there, but they tend to only sell things in big amounts.
We encourage anybody who finds a ready source of these things to post the information to the discussion group and we will incorporate it here later.
Good brewing, and happy yeast culturing,
Shout
Graham & Steve
