Saturday, April 20, 2013

Dry Yeast Rehydration and "Closed Procedure"

Below is an article that I wrote with professional side brewing in mind. It can have broader applications for both amateur and pro brewers, so I hope you enjoy.

 Craft beer is booming. The past decade has seen a meteoric rise in the number of new breweries dotting the landscape. Along with that, many homebrewers have stepped in to fill the growing demand for makers of artisan beer. The goal of this document is to help ease this transition to larger scale brewing by tackling an important topic, and discussing a key concept to the brewing process: yeast handling. The hardest working employee in any brewery is the yeast. A brewer can craft the finest wort possible, but if they do not create an ideal environment for the yeast to generate the desired flavors in the beer, an opportunity is lost.
Brewers pay a tremendous amount of attention to fermentation temperatures, yeast strain selection, and re-pitching approaches.  An often overlooked aspect is yeast viability and the roll that rehydration plays in providing your yeast an opportunity to generate the flavors and attenuation levels you want. This document is aimed at the importance of rehydrating dry yeast, but also the "closed" process that it utilizes. It is applicable to handling liquid yeast as well as finings (Biofine, gelatin, etc.). These processes utilize common brewery equipment and is adaptable to various brewing situations.

Why Rehydration?
I remember my first dry yeast packet. It came taped to the top of the liquid malt extract can the resided in my inaugural English Pale Ale kit. The instructions were simple. After cooling my wort, I was to combine the yeast and wort in my fermentation bucket and the rest would be history. First of all let it be said that pitching dry yeast directly onto the cooled wort can make excellent beer. With that said, as I further immersed myself into my new hobby, I learned that the dry yeast instructions for professional brewers was different. I had to find out why.
There are many reasons why dry yeast manufacturers recommend rehydration. First and foremost is yeast mortality. When dry yeast is pitched directly onto the wort, approximately 50% of the yeast die (White & Zainasheff, 2010). Following appropriate rehydration instructions per the manufacturer ensures that you are pitching a larger number of live cells into your wort. Rehydration also prevents a large number of dead yeast cells from influencing the flavor, attenuation, and consistency of your beers from batch to batch. The good news is that rehydrating yeast is a simple process that can utilize many items that amateur brewers already have and are also common to larger brewery operations as well.
Process and Equipment Options & "Closed" Procedure
At Cranker's Brewery we have a 15bbl system where we utilize dry yeast for the majority of our beers. The equipment we use to rehydrate are the items we use, but there are other options to achieve the same goals. Here is a list of items used:

  • 5 gallon corny keg and the requisite disconnects
  • Beverage tubing
  • Triclover x barb connection
  • Triclover gasket and clamp
  • Use of our hot liquor tank (HLT)
Our process is simple. After cleaning and sanitizing the corny keg and all keg parts involved we draw hot water off of our HLT to the volume specified by the dry yeast manufacturer. This water has been charcoal filtered and has been held at 170 F for a minimum of twelve hours allowing us to put pasteurized water into our rehydration vessel (corny keg). We connect the triclover x barb connection to the butterfly valve on the side of our HLT, and allow the hot water to flow into the corny keg by opening the pressure relief valve on the keg lid. When the keg is filled to the appropriate level, we disconnect and allow the water to cool to 105 degrees F over the course of our brewday.
When wort production is finished and the wort has been transferred to the fermenter, we begin the rehydration process. This is also where we begin use of our “closed” procedure. CO2 gas that is at 35psi is placed on the corny keg and the pressure relief valve on the keg's lid is opened. This allows the keg lid to be removed and placed in sanitizer. At this point there is a plume of CO2 gas that begins to flow out of the top of the keg. This plume is what prevents dust that bears beer spoilage organisms from falling into the keg. The dry yeast packages are then removed from the sanitizer that they were previously placed in and cut open with a sanitized knife. We then pour the entire contents of the yeast package into the 105 degree water. At that point, the keg lid is replaced and the pressure relief valve is closed. CO2 gas is then shut off. Once the yeast has received it's allotted thirty minutes of rehydration time, it is pumped into the fermenter with CO2 pressure using the same triclover x barb fitting that was used to take water from the HLT.
This method of utilizing positive pressure from the CO2 supply of the brewery is an effective way of creating as close to a closed transfer as possible in our brewery. This technique can also be applied to pitching liquid yeast, dry hopping, and using fining agents. With finings and dry hopping, the use of positive CO2 pressure allows the brewer to complete these standard brewery practices with minimal ingress of oxygen into the finished beer, thus minimizing one of the largest factors in beer staling.
Rehydrating dry yeast and utilizing “closed” transfers in the brewhouse are two ways that new and veteran craft brewers can make strides in beer consistency and stability. The equipment used in your brewery does not have to be identical, making the overall process adaptable and accessible to a wide range of situations. Hopefully these guidelines and concepts will be beneficial and employable in your workplace.

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