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Custom Yeast Propagation
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Custom Yeast Propagation
Call For Pricing
(760) 519-0849

Pitching rate or final cell count , C2 = number of cells/ml when diluted in final volume of wort to be fermented. To determine final cell count C2, use the dilution equation C1 X V1 = C2 X V2, where C1 is the cell count shown on  RBY yeast product label, V1 is the volume of slurry used, and  V2 is final volume of wort. Convert to  volumes to ml (10 barrels = 1,170,000 ml). Solve for C2. C2 = (C1 x V1)/V2. C2 should be between 5-10 million/ml for a 1.040 beer. 

 

 

 

 

 

Problems with beer spoilage have occurred since the dawn of fermentation. Those problems have spurred many inventions, including stainless steel fermenters, addition of hops to retard lactic acid bacterial growth and the accidental invention of cold fermenting lager yeast that grow in conditions too cold for most spoilage organisms.

In leu of these technological improvements, most brewers have run into a case where “bottle bombs" or "gushers" form months after a thoroughly finished and dry beer has been bottled. Other times bottles go sour months after bottling. I’ve tasted kegs from breweries lately that have the distinctive horse blanket/sour from Brettanomyces in an IPA made with only Chico Saccharomyces yeast.

 

How does this happen? It’s the dreaded “C” word or contamination. Where does it come from? Since most modern fermentations are closed to air, the short answer is: dirty surfaces with living microbes or viable spores somewhere in the brewing process. Wort can be considered a wound up spring full of potential energy. There are many microbes other than brewers yeast ready and willing to unwind the energy to reproduce and spoil your beer! Contamination can have a devastating effect on cash flow.

 

Properly pitched yeast in combination with hops probably squashes most beer spoilage organisms due to rapid formation of alcohol and pH drop. But, even a few strong survive, they will raise their ugly heads later when they find their niche, and unfortunately may end up in customer’s hands (yikes). I’ve seen a trend where breweries are serving beer that didn’t make it and calling them sours. I’ve seen their books go sour as well. Only purposely inoculated sours should be served.

Keeping things clean 

 

Homebrewing is easy if all surfaces and the inside of hoses and pumps are cleaned with 180oF detergent with a high pH and physical scrubbing with brushes, and a sanitation step with an oxidizer like iodine or an acid detergent like Star San.

 

But, as homebrewers progress to professional brewing, homebrewers have a tendency to think that homebrew sanitation is sufficient for large brewing systems. Professional brewers use a technique call CIP or Clean In Place. This requires much more powerful chemicals to first lyse cell membranes on the surface of stainless and hoses using a spray ball and hydrostatic pressure recirculation in 180o F, 0.2% (0.05M)  to 2.0% (0.5M) sodium hydroxide or “caustic”. In this cleaning step, caustic causes fat component of membranes to be broken down into glycerol and free fatty acids. After a good recirculation cleaning step with caustic that includes every nook and cranny, no membranes should be intact on any surface. Every surface that comes in contact with wort cooler than boiling must be cleaned. Especially problematic are pump heads, heat exchanger plates and hoses where biofilms are formed. Even the hot side should be cleaned with a least caustic.

PBW and other detergents don’t have caustic to lyse membranes, and I am surprised how many professional brewers clean in place with a homebrew reagent.

Next, after the cleaning step with caustic, the equipment must be sanitized with an acid based oxidizer. This takes care of any spore formers that have rugged outer cell wall components that may be resistant to caustic. Oxidizers trash proteins and biomolecules, and cause cells to pop open. This reaction can be completed at room temperature. The best sanitizer according to most experts is peracetic acid or PAA. PAA breaks down into acetic acid after the peroxide is reduced by a target molecule such as a membrane or spore coat protein.  75 ppm (mg/L) PAA kills 100% of target organisms in 30 seconds. The low pH causes stainless to passivate and form the antimicrobial chromium oxide layer. Low pH also dissolves calcium deposits or "beer stone”.

Further, professional brewers can monitor the CIP regimen by swabbing surfaces and plating on petri plates. Beer should be assayed for microbial contamination to check for contamination. This subject will be cover in the next article.

 

Using these cleaning and sanitizing agents properly and performing qc assays on equipment and beer, the brewer can gain confidence that no other organisms are growing in product batch after batch.

 

What’s the deal about pitching rates?

Whether you are brewing 5 gallons or 500 barrels, the number of living yeast cells introduced at pitching is critical for proper fermentation performance. Every wort, fermenter, oxygenation system, and yeast strain is different, so most brewers agree that “hitting it out of the park” is best way to avoid incomplete fermentations. The number of living cells/ml in a liquid starter culture is determined by RBY labs and is shown on each label. RBY labs suggests over 100 billion cells/5 gallons for low gravity fermentations, and over 200 billion cells/5 gallons for gravities higher than 1.060. This translates to 5 million cells per ml for low gravity worts under 5% ABV, and 10 million cells per ml for higher gravity beers.

Biology behind the pitching rate

If pitched at a low rate, yeast cells spend too much energy dividing, and can flocculate out early. If pitched at a higher rate, the yeast directs more energy toward turning over the carbohydrates and nutrients in the wort, and making the desired CO2 and ethanol instead of dividing. The transition between aerobic and anerobic fermentation takes time and energy. Also, oxygen is required for essential sterols and unsaturated fatty acids required for alcohol tolerance. That is why shaking or oxygenation of wort prior to pitching works so well because it buys more aerobic energy before the yeast start transitioning to the anaerobic state.

It is a big deal.

If you have problems controlling fermentation conditions (especially temperature), oxygen, or supplement your brewing with simple sugars, use more yeast to be safe. If in doubt, buy 2-3 RBY 5 gallon pitches for each five gallons to ensure proper yeast performance.

Subcategories

RBY Strains Tasting Notes

Strain #

Name

Source

Attenuation

Fermentation temp (F)

alcohol tolerance

Flocculation

style

tasting notes

RBY1

The One

Sierra Nevada PA

73-80%

65-75

11%

med

ale

Neutral all purpose, clean crisp. Hint of apple above 75F

RBY2

Lucky 7

Whitbread

70-80%

64-72

10%

high

ale

Dry and neutral with plum and raisin notes.

RBY3

Ye Old English

Munton's

60-70%

65-72

8%

low

ale

Powdery, slight fruit and sulfur

RBY12

Monk

Westmalle

74-78%

64-85

14%

med

belgian ale

Banana, clove, bubble gum, spice, apple. Neutral compared to other Belgian strains

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