Info

I Oxygen I candle

Wort pump

Back pressure valve

To fermenter

Fig. 6.5 Automatic pitching rate control system using NIR turbidometry.

has a rapid start and all of the yeast is exposed, more or less simultaneously, to the transition from storage conditions to suspension in oxygenated wort. Arguably, this offers the best chance of ensuring good control of fermentation, as discussed subsequently (see Section 6.4). The operating range of the turbidometric pitching control system requires the yeast to be dosed in throughout all or most of the period in which wort is pumped into the fermenter. This is probably not a serious problem if the collection time is short and it promotes efficient dispersion of yeast throughout the wort. However, with very large capacity fermenters, taking several hours to fill, continuous pitching is undesirable. Thus, it may be a cause of lack of control since yeast pitched early, and therefore exposed to oxygenated wort for considerable time, will be in a different physiological state to that pitched later.

The turbidometric approach provides demonstrable improvements in pitching rate control compared to a conventional system based on metered addition of a known wet weight of yeast. The data in Table 6.1 shows the range of values of suspended yeast count, measured with a haemocytometer, of samples removed from production scale fermenters at the completion of wort collection. The data is for six different yeast strains, where pitching rate was controlled by conventional methods and using the NIR turbidometric control system. It may be seen that with most beer qualities the range of yeast counts associated with the automatic system were significantly reduced compared to those which used conventional pitching rate control. However, in two instances (ale 1 and ale 2), the automatic system was of no advantage. Coincidentally, these two fermentations used flocculent yeast strains and this highlights one of the disadvantages of turbidometry. Thus, the correlation between particle number and turbidity is highest where the particles are of

Table 6.1 Yeast counts measured in fermenter at the end of wort collection for various beer qualities using conventional and NIR turbidometric pitching rate control (Boulton & Besford, unpublished data).

Measured cell counts (cells ml"1 x 106)

Table 6.1 Yeast counts measured in fermenter at the end of wort collection for various beer qualities using conventional and NIR turbidometric pitching rate control (Boulton & Besford, unpublished data).

Measured cell counts (cells ml"1 x 106)

Beer

Target pitching rate

Conventional*

Brew Your Own Beer

Brew Your Own Beer

Discover How To Become Your Own Brew Master, With Brew Your Own Beer. It takes more than a recipe to make a great beer. Just using the right ingredients doesn't mean your beer will taste like it was meant to. Most of the time it’s the way a beer is made and served that makes it either an exceptional beer or one that gets dumped into the nearest flower pot.

Get My Free Ebook


Post a comment