Making Slants for Yeast Growing

I bought some glass tubes with metal, autoclavable, screw caps from ebay this week for making slants.  I already have a load of pyrex tubes with plastic stoppers but the yeast dries up very quickly in those so I thought I'd try these.

A slant is a tube containing a solidified wort (growth medium) that you innoculate with yeast in order to keep a small number of yeast cells from a starter or a batch of beer for use in a later batch. 
The growth medium is sloped up the side of the tube to make it easier to lay the yeast cells onto it quickly to limit the risk of infection.  It's a great way of making a tube of liquid yeast go a long way but it's also good fun in a sort of geeky way.

So making slants is very easy.  I use a wort of about SG 1.015 and then I add about 3-4% agar to that.  For me this means adding 260g of water to 12g of light, dried, malt extract.  I then boil this up and add about 9g of dried agar (agar agar if you want to be pedantic).

I then take a syringe and put 10 ml of this sticky worty mixture into each tube.  The tubes hold about 30 ml so by the power of mathematics I make that about a third full.  I then put the lids on loosely and cooked them in the pressure cooker for 15 minutes.

Now, I keep the lids on loosely so that the tubes don't explode when the pressure builds up in the pressure cooker.  It also helps to keep the moisture out of the tubes.  Then I put the lid on the pressure cooker.

Once they've been cooked under pressure for 15 minutes I turn off the gas and allow them to cool enough for the pressure to equalise in the cooker.  If you don't do this and you release the pressure too quickly the wort will bubble up in the tubes and you'll end up with a sticky mess in the pressure cooker.  I don't know about you but I'd be very unpopular if I did this!

While the tubes are still too hot to handle I remove them one by one and rest them on a piece of wood with the, still loose, caps higher than the closed end.  This allows the wort/agar mixture to solidify in the tube at a jaunty angle ideal for growing yeast on.  Once they're cool they can be stood upright and the lids tightened.

Before they're used for yeast it's a good idea to prove them for a few days in a warm place.  The airing cupboard is good for this but anywhere about 20-24ºC is fine.  What you're doing here is making sure that nothing grows in the tube.  If anything does grow then you've got an infection and the slant's no good.  Clean the tube and start again!

Hopefully in a few days time I can show you how I innoculate the slants.