Lesson 3 - Wort Boiling Theory SAQ

***You have been asked to reduce the evaporation during the boil from 8% to 4% on a trial brew. What do you need to check after the trial brew before you can conclude that this reduction has not affected quality? And how will you check it?

Response:

This question gives us a good opportunity to discuss how we measure the effectiveness of a boil. A change in evaporation without a modification to the boiling system is likely to have resulted in a reduction in the amount of thermal energy applied to the wort. We should therefore evaluate the aspects of wort quality that are affected by the input of thermal energy. Below is a list of the outcomes of boiling with the analyses that we can undertake to confirm that they have been achieved, or not changed substantially. Some of the tests aren’t covered until module 2 of this course but as this is a *** question, we have summarised them in the answer.

1. Inactivation of malt enzymes: We could analyse wort sugars by high performance liquid chromatography (HPLC) or fermentability using a wort attenuation limit test, however it is very unlikely that any enzymes will survive the heat added to achieve a 4% evaporation, so these tests are probably unnecessary.
2. Sterilisation of wort: Wort forcing samples incubated at 27°C for 7 days will tell us if any organisms capable of spoiling wort or beer have survived. We could also culture membranes used to filter wort on nutrient agar to determine how many colony forming units of microbes have survived. Again, this is very unlikely so the tests may be a waste of time.
3. Concentration of wort by evaporation: We definitely need to measure this! Otherwise, we won’t know if we have reduced the level of evaporation. This is best determined by measuring density using a densitometer or hydrometer before and after the boil and calculating evaporation based on the increase in gravity. You could also use level measuring devices, or the mass of steam or electrical energy supplied to the kettle.
4. Development of flavour and colour: The colour of filtered wort can be measured using a spectrophotometer at 430 nm or by comparator. Flavour is more complex. GCMS can be used to check the wort produced by each evaporation rate and the chromatograms produced compared. Sensory analysis of the finished beer using a trained and screened panel who regularly assess the beer is also necessary as the GCMS can only measure volatiles.
5. Extraction and isomerisation of hop compounds: Bitterness units can be measured using either extraction into 2,2,4-trimethylpentane and analysis using a spectrophotometer or using HPLC. Hop aroma compounds can be measured using GCMS. We should measure both as both bitterness and aroma are important components of beer flavour.
6. Formation and precipitation of protein/polyphenol complexes: This can be evaluated using an Imhoff cone where the level of sediment produced and wort clarity are assessed. We would also need to determine the change in level of coagulable protein. This can be determined using the Kjeldahl method on wort after each boil. Nitrogen levels on samples of wort taken after the standard and trial boils should be measured before and after boiling in a lab for five hours at 105-108°C. The difference in the reduction of the level of coagulable protein produced by each boil can be used to determine the effect of the change in evaporation. In wort boiling, we are trying to remove nitrogenous material that causes beer haze or in extreme circumstances coats yeast causing problems in fermentation. We should therefore check fermentation rates and yeast viability are unchanged. For haze we can check the finished beer for sensitive proteins, measure the saturated ammonium sulphate precipitation limit or carryout haze forcing tests on packaged beer.
7. Removal of unwanted volatile flavour compounds: DMS is the main culprit here so GCMS could be used to measure its levels. We could also use GCMS to check the levels of the aldehydes characteristic of unboiled wort such as isobutyraldehyde, 3-methylbutanal, 2-methylbutanal and 3-methylthiopropionaldehyde in wort from the 4% and 8% evaporation boils. We could also evaluate the condensate produced in the stack drain or vapour condenser in two ways. We can analyse it for flavour compounds such as aldehydes, furans, ketones, pyrazines and sulphides using GCMS or we can physically check its odour. Condensate early in the boil should smell worty and grainy but it should be largely odour-free before the end of the 4% evaporation boil
8. Acidification of the wort: This is an easy one. Measuring the pH of the wort with a pH meter will confirm the pH is as specified for the brand.
9. Activation of foam stabilising proteins:  This relates to the foam stability of the beer produced. This can be measured using the NIBEM method where foam is formed by a machine and the rate of foam collapse over time is measured. NIBEM analysis can be carried out on the beer produced by the 4% and 8% evaporation boils. If you have a brewery with a very sophisticated lab, you could even measure the level of protein Z and LTP1 and its glycated form.