Monday, 10 November 2014

How much yeast?

I need yeast, lots of yeast, and yeast is quite expensive...

I've been asked to brew a beer using honey by a friend who keeps bees, after a bit of thinking and searching I've decided to brew a version of Charlie Papazian's  Rocky Raccoon's Crystal Honey Lager.

I did an extract version of this years ago and although I have no notes I do remember it being really nice, so a full mash version sounds like a winner.

Now, yeast is a bit of an issue for Lager, pitching rates are even more important for various reasons (lower fermenting temp means less growth, means you need to start with more, less growth and straight into fermentation is better if you want a clean beer with low esters).
The Mr Malty pitching rate calculator suggests that I need nearly four 100% viable vials of yeast, which would cost about £30, or more like six if the yeast is a month or more old (v.likely in this neck of the woods). That is not much change out of out fifty quid!

You can of course build up a starter, but again the numbers look bad for just a simple starter, I'd need to grow up a 7.6 litre starter!

To deal with this I thought it was about time I build a stir-plate (there are loads of ways, mine is thrown together from a computer fan, some magnets, a sandwich box and some wire) and get growing the yeast up as efficiently as possible. Stir plates keep the yeast from flocculating and continually aerate the starter, giving you the most cell growth by volume. With a Stir Plate the calculator suggested that I would need a starter of 2.8l, which is a bit easier to handle.

Except my largest flat bottomed flask is only 2l....

Step up YeastCalc, an even more sophisticated tool than Mr Malty's.

What YeastCalc does is allow you to work out the steps you need to get up to the required number of yeast cells, up to three steps are available, which should be enough for me with 19-23ltr batches and beers that rarely go over 1.060 OG.

I decided to go with a 1ltr starter first, then move to a 1.4ltr, this should give the existing yeast cells something worth eating on the second step and sufficient growth to hit the target (ok I'm likely to be 1 billion cells short, but what's a billion between friends eh!)

It's pretty easy really, just boil your 1lts of water (I use bottle spring water, no other treatments) with 100gm of light Dry Malt Extract (DME), by using a borosilicate glass flask it's possible to do this straight on my halogen hob.

Cover the mouth of the flask with sanitised foil to stop any dust or other crap falling in.

While it's boiling take your vial or smack pack of yeast out of the fridge (you do store it in the fridge right?) and let it warm up to room temperature.

After about 10 minutes, move the flask from the heat and allow to cool for twenty - thirty minutes (you can put these flasks straight into cold water, but there's no rush and you do hear stories of them breaking sometimes.)

Then place the flask in a sink of cold water to take the temperature down further, I find that after about another fifteen minutes it's about right, but leaving it on the kitchen worktop for a while means that both it and the yeast should be pretty close in temperature after an hour or so.

Sanitise the yeast pack, shake well, if using a vial open it slowly, they often gush if done too quick, then pour the yeast into the starter.

Some people boil their stir bars in with the wort, they are after all designed to be autoclaved, but I had mine sitting in a shot glass with some Star San. Drop the stir bar into the wort and then place the flask on the stir plate, switch on and leave for 36 to 48 hours.

Because it's lager yeast I set my fermentation "chamber" (fridge) to 12 deg c, I'm going to leave it the full forty eight hours before crash cooling overnight, then discarding the beer before adding in another 1.4ltrs of wort and then fermenting again for another two days. After than I should be ready to brew on Sunday!

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