Magnesium

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Magnesium (Mg2+) is a mineral naturally present in water and grain. It's an important component of beer flavor, imparting a lightly sour and astringent or bitter character. Magnesium is also a necessary nutrient for yeast growth and fermentation, although only a low concentration is required. This ion behaves similarly to calcium but is less effective at reducing mash pH.[1]

Suggested levels

  • Wort level of at least 5 mg/L is needed in order to support fermentation[1]
  • 40ppm magnesium is considered to be a reasonable maximum concentration in the brewing water.[1]
  • Levels higher than 125ppm in beer have a laxative and diuretic effect on the consumer.[1]
  • There seems to be no consensus about what levels are ideal, but many brewers consider magnesium in the water to be greatly beneficial.

Sources

  • Grain - A 10°P malt wort provides around 70 mg/L magnesium.[1]

Effects

  • Lower mash pH by precipitating phosphates, although not as effective as calcium.[1]
  • Improved enzyme function, such as yeast pyruvate decarboxylase.[1]
  • Flavor - at moderate levels, mg can enhance a beer's character by providing a sour, astringent flavor.[1] at excessive levels, the sour and bitter notes can become unpleasant and harsh.[1][2]


If Mg is absent, yeast cannot grow. Its most important role is being directly involved in ATP synthesis, the form of energy used within cells. If Mg is limited, yeast are forced to produce compounds that can compensate for some of its other functions. Mg also plays a role in preventing cell death when the concentration of ethanol builds up within the cell, and has also been shown to improve the cells ability to withstand stress.[3]

Magnesium acts in a similar manner to calcium, but owing to much better solubility of the corresponding salts, magnesium is not as efficient as calcium. The mash pH decrease is caused by the reaction and subsequent precipitation of the phosphates from the malt, which coincides with the release of H+.[4]

Magnesium is not thought to have an impact on palate until at above 30 ppm when it gives a sour bitterness.[5]

Magnesium ions (Mg2+, at. wt. 24.32) are needed by many yeast enzymes, such as pyruvate decarboxylase. In some respects the effects of this ion resemble those of the calcium ion, but the effects on pH from interactions with phosphates are less pronounced, being about half, because the salts are more soluble. While high concentrations of magnesium ions are unusual, they can impart a sour or bitter flavour to beer. High, laxative concentrations are not reached. An upper limit of 30 mg magnesium ions/litre has been proposed.[6]

magnesium ions interact with mash components such as inorganic phosphate, phytic acid and less phosphorylated inositol phosphates, peptides, proteins and probably with other substances displacing hydrogen ions into the mash and reducing the pH.[6]

Ions of Mg2+ can contribute a bitter and sour flavor, which increases with levels above 70 mg/L. These flavor effects appear to depend on a balance between the Mg2+ and Ca2+ ions.[7]

Mg2+ has some influence on pH control, but since Mg2+ salts are more soluble than Ca2+, they are less effective. Mg2+ is the most abundant intracellular divalent cation in yeast cells. It has a central role in governing yeast growth and metabolism, and it acts primarily as an enzyme cofactor for enzymes such as pyruvate decarboxylase. Mg2+ neutralizes the anionic charges on nucleic acids and proteins. It has a direct bitter/sour effect on beer flavor.[7]

Magnesium is a mineral required by yeast for growth, and its addition can sometimes speed up fermentation activity. For this reason, the addition of some magnesium, usually as magnesium sulfate, to brewing water may be desirable. The amount should not exceed 20 mg/L (parts per million), measured as free magnesium.[8]

Mg2+ in concentration over 15 mg/L can affect a sour or bitter astringency found in beer [61].[9]

Concentration of wort magnesium typically falls in the range of 50–90 ppm and appears to be directly related to concentrations found in malt. This relationship is apparently due to the high extractability of Mg (up to 80%) compared to that of other metals94. Mg content of cells peaks early in fermentation and is thereafter decreased as cell mass increases and Mg is effectively diluted165. Yeast cells have an absolute requirement for Mg, which acts as a cofactor for many enzymes and is necessary particularly for enzymes involved in glycolysis224. Efficient conversion of sugar to alcohol is therefore dependent on an adequate supply of bioavailable Mg. This is of critical importance for brewery fermentations, where worts typically contain sub-optimal levels of Mg and where Ca ions may have an antagonistic effect on Mg ion uptake. Walker and Maynard225,226 have shown that Mg is also required for cellular growth and division in batch culture under glucose repressed conditions and increased growth rate in chemostat culture is associated with increased cellular Mg levels225,226. Increased uptake of oxygen and increased ethanol production also suggested an increase in respiro-fermentative activity in yeast cultures incubated with increased Mg225. Mg is cited as one of the most important ions present in brewery wort in terms of fermentation performance. Supplementation of both standard (12°P) and high gravity (20°P) worts with Mg (500 ppm) results in higher fermentation rates, increased uptake of maltose and maltotriose and increased production of ethanol, with up to an extra 5 mL ethanol L–1 produced during high gravity fermentation when Mg had been added as a supplement172,174. This promotion of fermentation performance by Mg was observed for both ale and lager strains172,174 and later with wine yeast fermenting grape must. It is probable that most brewery worts do not contain optimal levels of Mg, and even when wort Mg was increased from a basal level of 75 ppm to 135 ppm, improvement in 16°P wort fermentation performance with a lager yeast strain was not observed31. An alternative to wort supplementation is the ‘pre-conditioning’ of yeast cells by propagation in Mgrich wort. The Mg-rich cells produced have greater ethanol productivity in subsequent wort fermentations than their ‘non-conditioned’ counterparts223. Such pre-conditioning can increase cellular Mg levels by several-fold, depending on the Mg concentration of the propagation medium and duration of exposure191. Much of this Mg may be released when cells are pitched into fresh fermentation wort and this phenomenon has been proposed as a measure of the potential fermentation performance of a pitched yeast147. When considering the potential of Mg to improve yeast fermentation performance, the concentration of wort Ca should also be taken into account. Ca and Mg act antagonistically and any observed improvement may be related to the Mg:Ca ratio rather than the absolute concentration of Mg. Rees et al.172 reported faster fermentation rates at Mg:Ca ratios of 17:1 and 11:1 for 12°P and 20°P worts, respectively, compared with unsupplemented worts with Mg:Ca ratios of 3:1 or 2.5:1. Bromberg et al.31 did not observe an improvement in fermentation performance with higher Mg relative to Ca, though in that case the highest ratio present in wort was 4:1. Mg ions can positively influence flocculation and at a concentration of 10 ppm may substitute Ca under experimental conditions195. This characteristic may be relevant to brewery fermentation where the wort Mg concentration can be several fold greater than that of Ca172. Promotion of flocculation in a lager strain by Mg occurred between 12.5 ppm and 25 ppm Mg and was reversed when the Mg concentration was raised to 2,500 ppm. Increased flocculation of cells from a top-fermenting ale strain was observed at 2,500 ppm Mg51. The deflocculation of lager strain cells at 2,500 ppm Mg may be due to competition of Mg for the Ca-lectin binding sites51. Mg-induced flocculation is more sensitive to the presence of metal-chelating agents than Ca-induced flocculation and it is likely that the greater specificity of Ca in yeast flocculation relates to a greater affinity for cell wall-binding sites51,198. Smit et al.190 reported that onset of flocculation was triggered in a lager strain by the depletion of any of a number of different nutrients from the growth media. The exception was Mg, the loss of which did not result in flocculation, suggesting that nutritional Mg has a role in the process. This role is not fully understood but may relate to cell surface hydrophobicity, which is reduced in cells grown in Mg-limited media (0.7 ppm). Inclusion of Mg in the assay medium did not increase the hydrophobicity (or flocculation potential) of the cells in that study190. Apart from the metabolic requirements of yeast for Mg during fermentation, these ions also have a well-documented role in protecting yeast from the toxic effects of ethanol and may therefore influence fermentation performance during higher gravity brewery fermentations. Mg supplementation reduces the toxic effect of ethanol in defined media. Walker222 reported viabilities of 0% and 53% in a wine strain exposed to 10% ethanol for 24 hours in the presence of 50 ppm and 500 ppm Mg, respectively. Likewise, Hu et al.88 showed that 9 hours of exposure of yeast cells to 20% ethanol led to the death of all cells in a population, whereas supplementation of the same medium with 85 ppm Mg resulted in viabilities of between 25 and 55% depending on duration of Mg exposure. Increasing Mg concentration led to increased resistance of brewing and distilling yeast to the toxic effects of ethanol222. It was proposed that Mg exerted its protective influence on the plasma membrane and, interestingly, Mg also protected cells against the effects of heat shock222. Ethanol and heat shock affect cell membranes in a similar manner164 and Mg may therefore have a general protective effect on the yeast cell plasma membrane. Increased membrane permeability in response to ethanol exposure is well documented40,75,103,169,182 and the protective effect of Mg has been attributed to its ability to prevent excessive loss of ions162 and nucleotides88 from the yeast cell. The presence of Mg obviates the requirement for heat shock protein synthesis, which would otherwise be needed to maintain plasma membrane integrity on exposure to ethanol23. Increased resistance to ethanol is conferred regardless of whether Mg is included in the yeast growth medium as a pre-conditioning step or whether it is added as a supplement concomitant with ethanol exposure23,88, raising the question of how exactly it acts to maintain plasma membrane integrity under stressful conditions. Increased availability of Mg during higher gravity brewery fermentations may also benefit fermentation performance by mitigating the effects of osmotic stress on the cells47. Improvement of fermentation performance and stress tolerance of brewing yeast occurring as a result of Mg supplementation is clearly an attractive approach to increase productivity of higher gravity brewery fermentations. The potential negative effects of Mg on flocculation should however be considered, as well as the potential of these ions to influence the uptake of other essential metals such as Mn24 and the ultimate effect of Mg supplementation on beer quality indicators.[10]

A number of studies have shown that Mg within yeast extracts or foods can contribute significantly to the fermentation performance of yeast47,48,59. The implication being that addition of Mg alone may, in some cases, be more advisable than adding a complex yeast food.[10]

Mg is needed for yeast nutrition, and it is likely that there is enough in the malt for this purpose, but a small amount in the water is a safeguard.[11] Magnesium ion has a very marked sour-to-bitter flavor, and can be detected in concentrations of around 15 mg/L.

Magnesium is widely appreciated to be an essential element for yeast growth and its biochemical functions are known to be numerous. The element is required for the function of over 100 enzymes (it binds to adenosine nucleotides).[12] Levels up to 5O ppm are normally supplied in microbiological growth media. However, chelated magnesium isn't available to yeast, so the level in wort doesn't give the full picture regarding how much the yeast can absorb.

in a brewery fermentation with a pitching rate of 107 cells/ml and a three to four fold growth factor the yeast would absorb a maximum of 30-45 ppm of magnesium. The quantity actually absorbed may be less than half this amount without there being any affect on yeast growth. Given that all the magnesium in the medium cannot be absorbed then effective levels in brewery worts could be expected to be of the order of 100 ppm. Although these calculations are based on experimental conditions well removed from those occurring in a brewery it is interesting to see that a survey of the literature indicated that the magnesium content of worts lies between 35 to 148 ppm with the majority of the samples in the range 95 to 139 ppm.[12]

Shortages of magnesium tend to affect the onset of fermentation rather than the eventual degree of attenuation.[12]

See also

  • Water - Expert guide to adjusting water minerals
  • Brewing pH - Discussion of pH throughout the brewing process, including the benefits of pH control by adjusting calcium.

References

  1. ↑ a b c d e f g h i Palmer J, Kaminski C. Water: A Comprehensive Guide for Brewers. Brewers Publications; 2013.
  2. ↑ Fix G. Principles of Brewing Science. 2nd ed, Brewers Publications; 1999.
  3. ↑ White C. Yeast nutrients make fermentations better. White Labs. Accessed 2020.
  4. ↑ Eumann M, Schildbach S. 125th anniversary review: Water sources and treatment in brewing. J Inst Brew. 2012;118:12–21.
  5. ↑ Howe S. Raw materials. In: Smart C, ed. The Craft Brewing Handbook. Woodhead Publishing; 2019.
  6. ↑ a b Briggs DE, Boulton CA, Brookes PA, Stevens R. Brewing Science and Practice. Woodhead Publishing Limited and CRC Press LLC; 2004.
  7. ↑ a b Taylor DG. Water. In: Stewart GG, Russell I, Anstruther A, eds. Handbook of Brewing. 3rd ed. CRC Press; 2017.
  8. ↑ Ryder DS. Processing aids in brewing. In: Stewart GG, Russell I, Anstruther A, eds. Handbook of Brewing. 3rd ed. CRC Press; 2017.
  9. ↑ Habschied K, Košir IJ, Krstanović V, Kumrić G, Mastanjević K. Beer polyphenols—bitterness, astringency, and off-flavors. Beverages. 2021;7(2):38.
  10. ↑ a b Gibson BR. 125th anniversary review: improvement of higher gravity brewery fermentation via wort enrichment and supplementation. J Inst Brew. 2011;117(3):268–284.
  11. ↑ Comrie AA. Brewing liquor—a review. J Inst Brew. 1967;73(4):335–346.
  12. ↑ a b c Saltukoglu A, Slaughter JC. The effect of magnesium and calcium on yeast growth. J Inst Brew. 1983;89(2):81–83.
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