Lesson 8 - Beer Properties End of Unit SAQ

*** “Beer leaving the brewery gate seldom, if ever, has an aged taste”.

        Considering this statement:

              a. Discuss the possibilities to extend beer flavour stability in the value chain from malt receipt to the point

                   of consumption.

              b. Debate which interventions would give the biggest impact.

Response:

Lipoxygenase enzyme (LOX) catalyses polyunsaturated fatty acid oxidation, mainly from linoleic acid. This forms hydroperoxides (oxidised fatty acids) which are underlying substances for a series of reactions that result in the formation of E-2-nonenal (the compound producing a cardboard flavour in aged beer).

1. LOX-less malt is available for brewing and beer brewed with it shows greater resistance to staling. LOX can also be reduced by storing malt before use, for up to 28 days.

2. Using darker speciality malts increase melanoidins, which possess antioxidant properties, scavenging hydroxyl and peroxide radicals.

3. Hammer milling is a more destructive milling operation and allows for the easier solubilisation of lipids from the malt kernel embryo.

4. LOX levels are reduced by mashing at higher temperatures up to 65 °C, where it is inactivated. Lower mash pH, e.g. 5.1 as opposed to 5.5, also lessens the activity of LOX.

5. Lipids extracted during mashing are removed during wort separation, and good bed formation and run-off practices (not collecting weak worts high in lipid) will limit carryover and later risk of oxidation reactions.

6. Bright worts are beneficial for flavour stability as they promote sulphur dioxide formation. SO₂ binds carbonyl compounds, masking their flavours.

7. During wort boiling vigorous boils are more flavour damaging, which precipitate the antioxidant polyphenols. Hop pellets contain high levels of polyphenols compared to CO₂ extract, which contain none.

8. Liquid adjuncts are generally beneficial to flavour stability as they contain low lipid levels.

9. Long boils and whirlpool stands increase thermal heat load and are negative to flavour stability; however, whirlpool stands should be sufficient to produce clear worts.

10. Post-wort cooling yeast health is important to remove residual oxygen and carbonyls, including diacetyl.

11. The yeast needs essential nutrients, including FAN and zinc (zinc is often supplemented as zinc sulphate). Good yeast management practices are key.

12. All transfers of beer need to be done with either:

    • De-aerated water

    • CO₂ packed mains and oxygen in process aids, made up with de-aerated water and purged with CO₂

    This applies to transfer to maturation vessel, filter, BBT, and packaging mains.

13. Filtration using kieselguhr powder introduces the risk of introducing iron into beer. Heavy metals, in particular iron and copper, should be excluded at all processing stages in brewing by use of stainless-steel pumps, pipework and vessels. In filtration, kieselguhr free filtration systems are becoming more widespread.

14. Modern packaging lines enable much lower dissolved oxygen (DO) levels in beer than a decade ago, in the order of 30 ug/L or parts per billion. This has resulted in a reduction in aged beer oxidation and has enabled longer flavour shelf-lives on beer.

15. DO may be reduced further, using oxygen scavenging crown liners.

16. After packaging, best practice is to keep beer cold and avoid agitation. This limits headspace oxygen from mixing into the beer. Some breweries have chosen to invest in this initiative despite the cost of cold chain distribution.

17. Within the distribution chain, correct stock rotation first-in-first-out or FIFO should be practised to avoid irregular ageing of stock. To assist with this, brewers label their packages with a ‘Best Before’ or ‘Packaged On’ date.

18. In deciding which factors are best to focus on, we need to understand the practical aspects of oxidation. We know yeast can mop up residual oxygen and staling compounds; post-formation, this is removed, leaving beer vulnerable.

19. It makes sense to work from the back end of the value chain and invest in modern packaging equipment to reduce DO first. After that we can look at reducing DO in bright beer tanks, then yeast health and only then brewhouse practices.

20. Outside the brewery gates, cool or cold distribution and storage could be considered, and of course, investment in the ability to monitor best practices in trade, such as FIFO, cold storage and gentle handling.