Lesson 8 - Beer Properties End of Unit SAQ

** Explain how you would approach developing an accelerated method to predict normal (ambient) beer haze stability for your brewery packaged beer.

What pitfalls could you foresee in accelerated shelf-life prediction?

Response:

The aim of a rapid or accelerated method to predict colloidal stability is to mimic the ‘normal’ colloidal shelf-life in the period after the beer has left the brewery. This requires you to decide on a median temperature for your distribution environment, which in turn, depends on the philosophy used. Not too long ago, a major brewer in the US employed a distribution cold chain, which inferred a much lower median temperature than in equatorial regions.

Often, 20 °C is chosen as a median for investigations. This is a convenient temperature because sample storage areas in the brewery can be easily kept at that temperature – as can trade outlets.

After the normal temperature is decided, we need to ensure that all normal shelf-life (NSL) beer is stored at the agreed temperature. We will need enough storage space so that we can measure samples weekly for haze.

Next, we have to decide on our accelerated regime. There are published protocols from ASBC, EBC and MEBAK. These involve developing a cycle of temperature extremes, for example, 24 hours at 60 °C followed by ambient cooling to room temperature then 24 hours at 0 °C. Your choice will also depend on logistics such as availability of chill baths and hot boxes, and their control.

After each hot-cold cycle, the haze is read at the lower temperature. Once the haze exceeds a specified value that consumers might react to, often 2-EBC, the accelerated or forced shelf-life (ASL) is exceeded and the test stopped.

The next step is to keep measuring the NSL on a weekly cycle after chilling a new sample from, e.g. 20 °C to 0 °C, until the top specification limit of haze is reached. This will determine the average trade colloidal shelf-life.

Now the ASL needs to be correlated to the NSL. If we assume that a linear relationship of haze increase is a factor for converting ASL, then its equivalent NSL can be derived at the 2 EBC readings:

ASL factor = (cycles at 20 °C/0 °C) / (cycles at 60 °C/0 °C)

This factor can be multiplied to the ASL cycle haze, giving us the equivalent NSL cycle haze at that week’s ambient shelf-life. This helps to predict ahead by three to six times.

To clarify, it may be that one week accelerated cycle equals four weeks normal cycle. Therefore, to achieve a predicted haze of six months ‘best before’ it could take seven weeks of testing weekly.

There are, however, some shortcomings in accelerated tests that need to be considered when implementing a protocol. These include:

          a. Different beers will show different characteristics, and each will need its own calibration, causing a lot of set up work.

          b. Raw material supplies change over a year and so will the ASL response, leading to further regular recalibrations.

          c. The extreme temperatures used in the ASL tests do not realistically mimic what happens, so they may not

              reflect what is going to happen in real-time.

          d. The development of haze is not necessarily linear, and this may make predictions inaccurate.