Tuesday, 9 February 2010

Beer Analysis

Having bought a microscope before Christmas I've been trying to put it to good use.  The reason I bought it, other than the fact that it's a brilliant boys' toy, is to give me the ability to check yeast count and viability.

Now that I've moved away from dry yeast I'm making large (4.5l) starters from White Labs vials.  This means that, as I step the starter up to the pitching volume, there's much more opportunity for an infection to sneak in.  The microscope allows me to see any nasties prior to pitching so I can have confidence that what I'm pitching is yeast and not some kind of bacterial soup.

The other task that the microscope can be useful for is to see if I can determine why a particular beer isn't very nice.  An example of this is a stout brewed by a member of our local homebrew club.  He brewed it for our March meeting last year and it immediately took on a rather sickly sweet taste and aroma.  Not being able to identify it, a bottle's been sitting in my garage ever since.  So I opened the bottle and had a look.

Firstly I checked the pH which was 5.  I'd have expected it to be between 4.2-4.5.  Then I checked the SG and it was 1.025.  So basically it didn't ferment out.

Then I took a look under the microscope and saw this.  What you can see is a few yeast cells looking healthy enough but then there are loads of rods.  These are lactobacilli.  These are the reason why it tastes so bad.  It's basically an infection due to poor sanitisation.  That's not to say that the equipment wasn't sanitised but it wasn't done so satisfactorilly.  A common reason for this would be topping up with tap water after the boil or using old, plastic fermenters with scratches that can harbour bacteria. 

Fortunately both of these are really easy to rectify. Make sure all your liquor is boiled for at least 15 minutes and if you have any suspicion that you may have a scratch in your plastic fermenter, no matter how small, replace it.  Fermenters are cheap in comparison to the number of batches of beer that can be ruined while you figure out where the infection is coming from.

So if you think about it, a 23 litre batch of beer costs somewhere around £12 to brew.  A new plastic fermenter costs £8.99 from Hop and Grape.  If I was using plastic for my fermentations I'd be considering replacing the fermenter every 4 or 5 batches as a matter of course.  Why take the risk?

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