Lesson 3 - Beer Foam SAQ
This Lesson allows you to test yourself on the material covered in the lesson Beer Foam, and to determine the level to which you have met the learning outcomes.
Suggested Response - Q3
** Discuss the two main foam stabilising proteins in beer explaining how they stabilise foam.
Response:
The two main foam stabilising proteins are:
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10 kD barley lipid transfer protein LPT1
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40 kD Protein Z
These proteins are surfactants or surface-active agents, which are amphiphilic compounds containing both hydrophilic and hydrophobic parts. The protein’s hydrophobic part associates with:
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The bubble gas interior and adjacent bubble interiors
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The hydrophobic hop acids, and
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The hydrophilic part with the liquid surrounding the bubbles
In doing so, they lower surface tension making the bubble more resistant to collapse.
To be effective, these proteins need to be:
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Relatively small and flexible
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Able to distribute themselves along the bubble wall to retard the physical effects related to bubble collapse, namely drainage, disproportionation and coalescence.
A model for their interaction is shown below:
Figure: Model of surfactant protein stabilisation of foam bubbles