Lesson 8 - Fermentation Unit Final SAQ

1. **Your brewery has a tank farm of 30 cylindroconical fermenters, each with an operating volume of 5,000 hL. You produce one beer quality, with a fermentation cycle time of 10 days. The fermenters require 12 hours to fill and a further 36 hours to cool, empty, and clean. The wort gravity is brewed at sales gravity of 12 °P.

a)    What is the theoretical maximum volume of beer that the tank farm can produce per annum?

b)    If high gravity brewing were introduced using a wort of 18 °P, with the result that the fermentation cycle time increased to 14 days, how would the theoretical capacity change?

2. **Answer ALL parts of this question:

a)    With the aid of a diagram, describe the relationship between diacetyl formation by yeast during fermentation and the pathway responsible for the synthesis of valine.

b)    What is the difference between VDK and diacetyl?

c)    Explain why VDK concentration reaches a maximum value in mid to late fermentation and then declines.

3. **Some brewing fermentations are spontaneous, using an inoculum made of mixtures of different yeast strains and bacteria. How do the metabolic potentials of the individual members of these mixed populations explain the sequence of events that are often seen?

4. ***Answer ALL parts of this question. Your brewery is beginning a major upgrade. Your role is to design the new fermentation plant. The current system of closed 500 hL box fermenters, arranged over four floors, is to be replaced with a tank farm of cylindroconical vessels, each with a capacity of 5,000 hL.

a)    Draw a diagram showing the principal features of the vessels you intend to install.

b)    What are the advantages that you expect to gain from the layout and use of the new tank farm?

c)    Do you foresee any gains to be made with regard to yeast handling and quality?

d)    What problems do you think will need to be overcome?

5. ***After reading the introductory information, answer BOTH parts of this question.

You are part of the NPD team for your brewery working on a project to introduce a new beer. Your role is to oversee planning of the fermentation trials, with a view to developing a suitable regime that meets the brief. You will have to use the existing tank farm of 5,000 hL cylindroconical vessels.

The new beer will be a pale pilsner type lager of 12 °Plato. Your marketing colleagues have decided it should have a marked fruity and floral character, derived from yeast during fermentation, but with the majority of its other flavour characteristics derived from malt and hops.

You will have to use an existing yeast strain that is quite highly flocculent and is currently used for high gravity brewing, which it tolerates but not well, based on the evidence that average crop viabilities are trending downwards towards 85-90%.

For reasons of economy the new beer will be brewed at high gravity (20 °Plato), using a wort made with 85% malted barley and 15% sugar adjunct. Fermentation fill times are 20 hours and require six 800 hL batches of wort.

a)    How would you propose that the fermentations be managed to encourage the development of yeast-derived flavours that meet the marketing brief?

b)    What yeast-derived flavour problems do you think you might encounter and how would you propose to minimise these effects?