Few quality tests are as simple to perform and informative to the brewer as that provided by time. Time and a little manipulation of temperature.
Forcing tests tell you the worst, the best and the likely condition of your beer at the end of production and in trade. Either cask or bottle. Moreover, they can be an essential part of your due diligence and so provide some legal standing in case of dispute. All they require is a controlled environment, some time and observation.
Firstly, take a simple example where you need to know whether your collected wort before pitch is contaminated with microorganisms. For this you simply collect a sample in a sterile container and incubate it at a temperature between 25 and 30oC. Observation of changes over the next few days will indicate the presence of spoilage. A clear beer without fermentation and with no surface skin or off-flavours suggests a clean collection. The presence of these suggests a problem.
In a more extended example you may wish to provide a shelf life on your bottled beer. For this take a dozen samples from the production run and incubate at 28oC for up to twelve weeks. Observe one bottle each week for clarity and contamination. The number of weeks the beer remains in good condition roughly indicates the number of months of shelf life in standard retail conditions.
Of course, it is impractical to wait 12 weeks before you stamp the shelf life on a batch of bottles but given constant production conditions it is reasonable to extrapolate from one batch to another. If differences are evident then comparison of batches will give you an indication of consistency.
Forcing tests typically involve accelerating the ageing of your sample and observing changes and problems before your customer does. In some cases, such as with wort samples, the results will be available before your beer leaves the brewery. In others it may be retrospective information for suggesting corrective action but also predictive against customer complaint. Either way it is valuable knowledge.
As suggested in the examples above forcing tests can be divided into those relevant to the brewing process and those applicable to finished product. Wort samples suitable for
forcing are typically those taken as the wort is collected into the copper. This is a critical point for contamination by microorganisms where even small numbers can rapidly multiply to cause problems, even in the presence of yeast. Similar samples taken at racking can indicate potential spoilage after fermentation.
Standard laboratory tests will be able to detect and identify contaminants and are important on a regular but intermittent basis. Forcing tests can be conducted on every brew, however, to provide a broader indication of consistency. Moreover, failed samples can be forwarded to the laboratory for detailed investigations.
It is essential that samples for forcing are collected in sterile containers. For this it is best to obtain disposable 30 or 60ml plastic bottles rather than chance an incomplete sterilisation of glass bottles or, more likely, the caps. During incubation remember that contaminated samples may ferment and produce pressure in the bottles so caps should be kept loose. Again, plastic bottles are preferable in case an explosion does occur and it is worth using gloves and goggles when you open any bottle.
Whatever your arrangements keep your samples well away from the brewhouse so that any contamination does not transfer to your fermentations.
Keeping your samples at constant temperature will require an incubator of sorts. Second hand laboratory equipment may be available at reasonable cost but it is possible to construct an insulated box with a small thermostatic heater to provide a similar service. In addition, a shelf with an illuminated back made of opaque glass will assist in visualizing clarity. Viewing a barcode through the sample bottle can help to further define the degree of clarity. Whatever test you devise try to keep a consistent approach and record your observations for future comparisons.
Forcing tests on bottled beer allow you to assess changes in the bottle by swirling the contents and also by pouring out a glass to see clarity, view head formation and check flavour.
Observations on forcing samples can be simply visual but should also include aroma and taste tests. These allow you to compare samples to your expected flavours as well as using off flavours to identify the causes of faults. It’ s a hard job but all part of a brewer’ s lot.
More extensive tests can include microscope observations and pH measurements or perhaps haze or protein assessments on precipitations. In other cases, a high temperature accelerated test at 65oC or of a cycle of high and low temperatures followed by tannin titrations can indicate protein stability. However, this level of dedication is some distance away from the use of forcing as a quick and simple indication of performance.
For the smaller brewery the ideal is a balance between time, investment and information. A few pots on a shelf provides at least the basis of this and the benefit of keeping one step ahead of your product.Return to Brewlab blog