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I've done a bit of research into different options of yeast storage and so far the least time consuming and most accessible methods seem to be:

  • Making a slant from a yeast sample taken directly from a freshly opened liquid yeast packet.

  • Taking a small quantity (about 5 mL) from a freshly open liquid yeast packet and storing it in a tightly capped test tube under distilled and deoxygenated water.

  • Taking a small quantity (about 5 mL) from a freshly open liquid yeast packet and storing it in a tightly capped test tube under 1.030 SG wort + yeast nutrient.

  • Making a starter with the liquid yeast packet and saving 10 mL of the yeast slurry in a tightly capped test tube.

All of the above methods will be done under sterile conditions and stored in the refrigerator.

Which one will work best for storing yeast for 4 months or so?

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Just do it

Nothing you described is needed or beneficial with modern liquid yeast packages. For example Weast's Activator:

The Activator™ package was designed with superior UV light- and oxygen-barrier material to extend shelf life, making our 6 month from manufacture date Product Warranty possible. Yeast slowly depletes energy reserves while in storage. The nutrient pouch inside the Activator™ helps the stored yeast recover from dormancy and restores vitality.

With 6 months guaranteed shelf life, you just need to buy them fresh, and store. That's all. Other manufacturers may not include nutrient pouch, so starter would be advised if they don't, but shelf life can be similar. Dark, airtight container will help.

Make starter after storage period, not before

Fresh commercial liquid yeast packet will have more live cells per ml than your starter. Unless you are experienced microbiologist with good hardware base - but if you were anywhere near that level, you wouldn't need to ask this question. So if you want to spend time making starters, do it just before you brew. Starter before storage may only hurt, starter after storage, or second step to your starter if you already planned it, will help. Much better use of your time.

Tightly capped tubes may be a bad idea

Yeast are alive. They breathe, increasing pressure. Don't know what your tubes are made of, but if they are glass, do not seal them. Not even deoxygenated water one - you don't know how to completely get rid of nutrient manufacturer provided, right?

Your conditions are not sterile

To make a starter, you need a lot of air. If you can afford air filters good enough to give you sterile air in sufficient quantity, you probably don't need to care about splitting packages or anything like that anyway.

To reuse yeast, use slurry from previous brew

Big beers can spend a month or two in fermentation tank. After that, you can collect yeast slurry, and keep it in storage for 2 weeks with no need for starter, and up to 2 months if you know how to wash them and make a starter. This gives you up to 4 months of relatively safe storage, without all these operations, and with high chance of success.

If you only brew twice a year, don't bother

Unless you work way below minimal wage, or minimal wages in your country are even more joke than in mine, your time spent on splitting yeast package probably costs more than a fresh package of yeast. Reusing slurry is only "free" if done relatively fast. So unless it's something extraordinary expensive, or something you expect to be unable to buy again, it's probably best to forget it.

  • I guess what I meant to say my goal was to split the original yeast pack in two. Save one part and use the other. Then repeat with saved part the process to produce more beer. In essence: get more than one use from the original pack of yeast. Why is it so bad to use deoxygenated water? – ScrapeHeap Mar 16 '16 at 2:46
  • @ScrapeHeap see my edit. And deoxygenated water is not bad in itself. It just does not prevent pressure increase. – Mołot Mar 16 '16 at 10:55
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Slants are a lot of work, and generally not worth it unless you're dealing with a strain that's not commercially available. Or banking a lot of different yeasts with limited space.

If you're just trying to get more value from yeast purchase. Do a double step starter on first use. What you don't pitch save in sterile Mason jars. You can repeat this process indefinitely.

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