Green Bullet Gold Yeast Count

As promised, I did a yeast count on the Green Bullet Gold.  For this I used a plastic container to hold my sample, a pipette, a hemacytometer and a microscope.  I just take a small sample of the beer, a few ml, from the sample tap on the FV.  I then draw a load of it into the pipette and squeeze it back into the sample a few times.  This helps to break up any clumps of yeast and also degasses it.

The hemacytometer is a thick glass slide that has two chambers each holding 1/10000 of a ml.  These chambers have an accurately grid etched into them which effectively allows you to count the cells in a known volume of beer. I take the coverslip and plonk it onto the hemacytometer so that it covers both of the chambers.  Then I draw a small quantity of the sample into the pipette before squeezing until a droplet is hanging off the end of the tube.  This droplet is then offered up to the edge of the cover slip where it is drawn ito the chamber.  I repeat this on the other chamber.  Take a look here to read more about how to do it.

Actively fermenting beer has about 60,000,000 cells per ml but as the fermentation subsides this reduces and the yeast drops to the bottom of the FV.  At racking you're looking for there to be about 1,000,000 cells per ml.  At this point there's enough yeast to ferment any priming sugar to carry out the secondary fermentation without causing excessive bottoms.  This means the cask will settle quicker and bottles will just have a film of yeast in the bottom rather than a thick sludge.

So, in my Green Bullet Gold I have 890,000 cells per ml which is typical of WLP002 or Fullers yeast.  It drops like a stone.  Based on this I'll set the FV temperature controller to start cooling in the morning and will rack to cask on Wednesday evening.

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?

Fullers yeast starter

Suppliers of liquid yeast tend to package it up in quantities that will only just ferment 5 gallons of yeast; so long as you aerate loads after pitching. You could obviously buy more of it but that can get expensive and, depending on how old the yeast is, you may end up just pitching a load of yeast with a high percentage of dead cells anyway as this stuff doesn't keep indefinitely.

The best way to be sure that you are pitching enough healthy yeast is to make a starter. I use a stir plate to encourage aerobic fementation as that's the time where the yeast reproduce making lots of fresh, healthy, new cells.

Here's a picture of my yeast starter for tomorrow's (actually today's) brew. It's about 4.5l of wort made with DME to an OG of 1.040 with a load of slurry from an earlier, unused starter added about 4 hours ago.

You can see my refractometer standing upright at the back of my stirplate. It's a great piece of kit that every brewer should have.

The cold weather came in handy tonight as I was able to bring the temperature of the wort from boiling to pitching temperature within minutes just by dunking it in a bucket of water that was sitting by the back door. After I broke the ice on it it was a perfect wort chiller!

As the source of the slurry had been sitting in the kitchen for a couple of weeks I did a quick check on the health of the cells prior to pitching. The photo to the right shows that the yeast cells are healthy. There's a little debris around but no nasties that I can see.

I'll do a viability check on the starter (using methylene blue as an indicator) prior to pitching into my wort. It it's infected (which I doubt, looking at the activity in the flask right now) I'll pitch a fresh tube of WLP002 and aerate like mad.