Stir Plate for Yeast starters

Whilst on our Michigan Breweries trip back in late May 2013 we called in the Homebrew shop located next to Bell’s Brewery & Eccentric Cafe in Kalamazoo (see here for the blog about this visit). One item of brewing equipment that we had long been wanting to invest in is a Stir Plate but they can be quite expensive ranging from $70-100+. There was one that we’d read about that is made by a Homebrew enthusiast located in Michigan which cost about $45. Bell’s Homebrew shop just happened to stock The StirStarter so we took the plunge especially considering we have some high gravity brews coming up over the next few months.

What are the benefits of using a Stir Plate you might ask? A Stir Plate is in effect a rotating magnet that in conjunction with a Stir Bar inside a flask of yeast and wort keeps the yeast in suspension and therefore has more contact with the wort to encourage cell growth. Having sufficient yeast to ferment wort is an important factor in having a healthy fermentation.

After a period of travelling it was time to brew up a batch of beer but this time using the Stir Plate. The beer in question was 10 gallons of Blonde Ale but split into 2 x 5 gal batches, each of which fermented with different yeast strains:

1. Wyeast 1099 Whitbread Ale – from a smack pack that needed using up.
2. Wyeast 1056 American Ale – from our yeast bank in the freezer.

Here are the main steps followed to prepare the yeast starters for this beer (please refer to a Homebrew book for concise instructions):

Step 1 – unpack and assemble the Stir Plate.

Clear instructions are included and the main point to note is that the top needed removing so that the packing material, which was inside for transportation protection purposes, could be removed. After removing the packing material the cover was re-fitted.

The contents of The StirStarter include:

• Stir Plate
• Power adaptor
• Instructions
• Stir Bar
• Magnet (to capture the Stir Bar)

Step 2 – prepare yeast.

The Whitbread Ale yeast was taken out of the fridge and the nutrient bag within it was ruptured by ‘smacking’ it then shaking it and leaving it at room temperature to begin activating.

The American Ale yeast was removed from the yeast bank in the freezer and the viles were placed in lukewarm water to begin defrosting. Once defrosted they was shaken to mix the contents.

Step 3 – prepare starter wort.

8oz of Dried Malt Extract (DME) was weighed out and added to 1 gallon of water (approx 4 litres) in order to produce a wort with a 1.040 gravity. The pan was then placed on the stove and boiled for 10 minutes.

Once the 10 minutes was up the pan was placed in a sink of ice and water to cool it down to 70-75 deg F. A hydrometer was then used to verify the Original Gravity.

Step 4 – cleaning & sanitizing.

As with all aspects of homebrewing it is important to both clean and then sanitize the various equipment involved and in this case that means the flasks, hydrometer, thermometer, air locks (including drilled bungs), and Stir Bar.

Step 5 – commence yeast growth.

Now that we had sanitized equipment, cooled wort, and activated yeast, the next step was to pour some wort into each flask, add the yeast to each flask, then fit the air locks. As we only have one Stir Plate, one flask also had the Stir Bar dropped in prior to the air lock being fitted. The Stir Plate was turned on and set to a gentle rotation with slight vortex. The other flask was periodically shaken and swirled to re-suspend the yeast.

Step 6 – pitching yeast.

After 48 hours there was sufficient yeast growth and the wort for the Blonde Ale had been prepared and cooled to 70-75 deg F so it was time to pitch the yeasts into the wort:

1. The Stir Plate was stopped about 8 hours prior to pitching so that the yeast could flocculate to the bottom of the flask.
2. The small magnet that came with the Stir Plate was used to capture the Stir Bar from the underneath of the flask and then slide it up the side of the flask PRIOR to pouring.
3. The liquid in the yeast starters was poured down the sink leaving the yeast and sufficient liquid to re-suspend the yeast by swirling it.
4. The yeast was added to each 5 gallons of wort together with yeast nutrient.
5. With it being summer and 85+ deg F the freezer in the basement had been preset to 67 deg F and the fermenter buckets were placed inside in order to have a controlled fermentation and avoid off-flavors.
6. Within 12 hours the fermentations had started.