Journal of the Institute of Brewing

Reflections

2024-04-03T00:48:54-07:00

As ever, the themes in this issue of Reflections are wide ranging. Last time I recognised the wonderful job our reviewers perform and how their contributions improve the quality of publications in this Journal (and elsewhere). This time, the focus is on the challenges of peer review and the importance of authors working together with reviewers (and the EiC) to make papers ‘shine’. On a happier note, ‘short communications’ will be introduced as a new category of manuscript to submit the Journal. Often, a neat, rounded piece of work is better suited to a standalone publication and can be lost in the push for a ‘big’ paper. Peer review and the usual rules will apply but the text of MS is no more than 2000 words with a maximum of 20 references. Finally, even in the refined world of scientific publication, it is good to celebrate success. The number of downloads is measure of reader interest and accordingly papers with > 400 downloads (and beyond) are flagged within an issue and across the archive.

Optimisation of Saccharomyces cerevisiae BRYC 501 ascospore formation and recovery for heat inactivation experiments

2024-04-11T04:58:19-07:00

Why was the work done: Ascospores from Saccharomyces cerevisiae BRYC 501 are useful biological indicators for validating the pasteurisation of beer. Ascospores are formed by yeast in response to low nutrient conditions and are characterised by greater resistance to stressors including desiccation, freezing and, during pasteurisation, high temperatures. Accordingly, the sporulation temperature of yeast ascospores, their shelf life, heat resistance and recovery need to be investigated.

How was the work done: The role of temperature in sporulation was investigated at 25, 27 and 30°C by measurement of the rate of sporulation over ten days. Shelf life of ascospores was established in deionised water at 1-5°C over 120 days by the measurement of heat resistance in McIlvaine's buffer. The recovery conditions of ascospores were determined using six agars after heat inactivation experiments in McIlvaine's buffer, alcohol free and lager beer.

What are the main findings: The sporulation rate of S. cerevisiae ascospores was highest at 27°C, and lowest at 30°C. Heat resistance of ascospores formed at 30°C was low with a D₆₀ value of <3 minutes, whereas at 25 and 27°C the D₆₀ was 8.8 and 9.2 minutes. The shelf life of ascospores was 60 days after an initial 14 days of maturation at both 25 and 27°C. The variation of heat resistance for ascospores grown at 25°C was shown to be lower than those grown at 27°C. Use of yeast extract-peptone-glucose agar to recover heat injured cells was > 200% higher than with the control agar.

Why is the work important: Sporulation should be performed at 25°C to produce the maximum number of spores for heat inactivation experiments. Spores can be maintained for 60 days, enabling several experiments to be performed. After heat inactivation experiments, ascospores should be recovered on YEPG agar for 10 days at 27°C

The effect of pasteurisation and storage on aroma compounds in lager

2024-04-30T07:11:35-07:00

Why was the work done: To investigate the impact of pasteurisation and storage in bottle on aroma compounds in pale lager beer.

How was the work done: Pale lager beer was produced at an industrial scale with 100% pilsner malt and a bottom fermenting yeast. Samples were taken of unpasteurised beer from bright beer tank, after flash pasteurisation and six months after packaging in amber glass bottles.

What are the main findings: Post pasteurisation, a marked increase was found in the concentration of 2,3-pentanedione (50%) and diacetyl (33%), presumably reflecting the decomposition by heat of precurser acetohydroxy acids. There was also a marginal increase in dimethyl sulphide (6%) with little or no change in other aroma compounds. Storage for six months in bottle, also resulted in an increase in the level of 2,3-pentanedione, diacetyl and dimethyl sulphide. The linear (Pearson) correlation was > 0.8 for both dimethyl sulphide and diacetyl, and 2,3-pentanedione and diacetyl. Accordingly, it was concluded that the levels in beer of dimethyl sulphide and 2,3-pentanedione are proportionally related to diacetyl.

Why is the work important: This work provides an insight into the effects on flavour and aroma of lager of flash pasteurisation and subsequent storage in bottle. The inter-relationship between aroma compounds in beer suggests that such synergies may undermine the sensory perception of threshold levels and identification of specific aromas.

Tracking dry gin volatile organic compounds over distillation: a time course study

2024-05-02T07:17:27-07:00

Why was the work done: The influence of distillation time on the volatile composition of gin has not been examined in detail at a commercial distillery.

How was the work done: Headspace Solid-Phase Micro-Extraction Gas Chromatography-Mass Spectrometry (HS-SPME-GC-MS) was used to tentatively identify 74 aroma compounds, with their concentration tracked in distillate samples over the course of three gin distillations.

What are the main findings: Four unique fractions were identified using Agglomerative Hierarchical Clustering: ‘heads’, ‘early hearts’, ‘late hearts, and ‘tails’. The hearts fraction (n=24 samples) was examined further, fitting statistically appropriate models to 54 aroma volatiles. Three sub-groups of volatiles were identified, (i) highly volatile monoterpenes with rapidly decreasing concentration over the early hearts fraction, (ii) volatiles whose concentration increased gradually over the hearts fraction and (iii) less volatile sesquiterpenes, sesquiterpenoids, and monoterpenoids which increased rapidly in concentration in the later distillate. Complex cubic models fit 34 volatiles with very high significance (p>0.0001) over the hearts fraction (72%). Informal aroma sensory bench testing identified distinct aroma categories with, for example, ‘Spicy’ being commonly detected in the later distillate.

Why is the work important: This investigation characterises the kinetics of flavour extraction over the course of a commercial gin distillation process. These findings highlight the potential for the expression of specific flavour characteristics by modifying the cut points of the distillation process

Guidelines to optimise the sensory detection of 2,4,6-trichloroanisole in neutral spirit and whisky

2024-04-23T07:48:04-07:00

Why was the work done: Guidelines are required to optimise the sensory detection of musty/stale taints in alcoholic spirits caused by 2,4,6-trichloroanisole. Early detection of the taint is necessary as the low sensory threshold can result in significant quality issues and masking the musty/stale off-note through blending is difficult.

How was the work done: The standard industry practice for ‘nosing’ is to dilute samples of spirit to 20% ABV to prevent sensory fatigue. It is not known if 20% ABV is the optimal concentration for detecting 2,4,6-trichloroanisole. In this study, the effects of ethanol concentration on the detection of the taint were evaluated using a sensory panel and gas chromatography-mass spectroscopy. The efficacy of nosing versus tasting to detect 2,4,6-trichloroanisole was investigated at different dilutions of distilled spirits. Further, the stability of this off-note at 20% ABV was determined to assess if the taint could be detected by nosing over a working day. Finally, the serving temperature of the sample was assessed in the sensory perception of the taint.

What are the main findings: The recommendations to optimise the sensory detection of 2,4,6-trichloroanisole in spirit samples are (i) nose samples at 20% ABV, (ii) as soon as possible after dilution conduct sensory tests and (iii) chill the sample.

Why is the work important: The limits of detection for conventional solid phase microextraction with gas chromatography-mass spectroscopy are typically above the threshold of human perception. Therefore, the industry needs to maximise the detection by sensory panellists of contaminated whisky samples to ensure the product does not go to market so as to avoid any reputational damage.