brewing water n.
Skip this Video
Loading SlideShow in 5 Seconds..
Brewing Water PowerPoint Presentation
Download Presentation
Brewing Water

Brewing Water

243 Views Download Presentation
Download Presentation

Brewing Water

- - - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - - -
Presentation Transcript

  1. Brewing Water 6 October 2008 A.J. deLange Burp Education Series Based on class given 28 April 1996

  2. Perspective • The community (and I) have learned a few things about brewing water since 1996 (when I last gave this class) • Then: Slavish attention to reproducing brewing cities’ ion profiles • A lot of people did a lot of hard work based on bogus data (published ion profiles) • Now: Emphasis on getting proper mash pH with brewing liquor that more or less matches traditional profile • Recognition of Residual Alkalinity as a powerful tool for evaluating and comparing brewing water samples • Tweaking “stylistic ions” to taste (and authenticity). • Why put it in if you are just going to take it out (e.g. Munich Helles)? • Often no information whatsoever on type of water required for a particular style - this is starting to change • Most modern water supplies are generally good for brewing most beers. • Big Exception: Chloramine!! Note: Red font denotes key concepts - take special note of these

  3. Approach • Water chemistry is intricate and detailed if not complex • In a couple of hours I can only skim the surface • There won’t be time to thoroughly explain many of the concepts • Go back and look at the slides again at leisure • Some slides are in here with that intention - we won’t do much more than mention them • For practical knowledge you must explore further on your own • Papers on CD • Most of the bloody details are found in the Cerevesia paper • Spreadsheet on CD • This will be your best friend in terms of practical applications. • Books (see list at end) • Internet

  4. There are Two Aspects to Brewing Water • I: Water chemistry has great influence on mash pH thus great influence on nature of the beer • Full understanding of this requires knowledge of acid-base equilibrium chemistry, intricate calculations… • Reviewed in Cerevesia article (on handout CD) • Fortunately, a simple (to use) Excel spreadsheet (on handout CD) can handle all of this for you • You need to know how to use it and what the numbers mean - not how to program it • II: Certain ions influence flavors - just as they do in any other form of cooking. • Salt to taste

  5. Your Goals • Understand • Relationship between beer and water it’s made from • Fundamentals of chemistry related to brewing water • Atoms, molecules, ions, moles, equivalents, acids, titration… • pH, Alkalinity, Residual Alkalinity (RA) and Hardness • These are the key concepts • Be able to… • Read a water report • Check it for validity (using spreadsheet) • Treat water to • Remove chlorine and chloramine • Reduce bicarbonate (alkalinity) and iron (if you have it) • Control the pH of your mash • Establish an approximation to a desired ion profile

  6. Quotations • “Wine is made by farmers. Beer is made by engineers.” (?) • “A distinction is frequently drawn in the industry between the theoretical man who tries to explain everything from a scientific point of view, and the practical man who relies on empirical knowledge and experience. A good brewer should be able to steer a middle course between these two extremes” - Jean deClerck • “The third group, the smallest, are the Noonanians, the triple decoction cultists. Eighteen hour brew days, elaborate water modifications: you wonder how they stay married.” - Delano DuGarm

  7. Quotations II • Water contains three ions which influence the pH of wort: bicarbonate, calcium and magnesium. The bicarbonate ion has a pH raising effect, the other two lower it. The pH lowering effect of magnesium ions is only half that of calcium ions. Depending on the ratio of the water’s content of bicarbonate on the one hand and calcium and magnesium on the other, the pH raising effects of the bicarbonate is more or less compensated or balanced. Thus experiment has shown that to balance 1 equivalent of bicarbonate ion 3.5 equivalents of calcium or 7 equivalents of magnesium ion are required. With respect to the pH raising property of the total alkalinity of the brew water, thus, a definite part is balanced. The remainder, the residual alkalinity, can serve as a measure of the pH raising effect of the water. • Paul Kohlbach, Die Einfluss des Brauwassers auf das pH von Würze und Bier, Monatsschrift für Brauerei, Berlin, Mai 1953 • Whole paper is on CD. Read it!

  8. Topics • Part 0: Beer and Water • Part 1: Fundamentals of Chemistry • Part 2: Carbon Dioxide, Water, Limestone, pH, Hardness,Alkalinity • Part 3: Adding Malt Phosphate to the Picture , Residual Alkalinity • Part 4: Water reports • Part 5: Water testing • Part 6: Water Treatment • Part 7: Synthesis of water with a given ion profile • Part 8: Comparison Beer

  9. Handout CD Contains… • A copy of this presentation • Translation of Paul Kohlbach’s seminal paper (1953) • A set of slides from a lecture given at DeClerck Chair XI (Louvaine-la-Neuve, Sept 2004) • Copy of the paper (based on that lecture) from Cerevesia 29(4) 2004 • Microsoft Excel spreadsheet which implements the significant brewing water chemistry calculations • Two part BT article on Alkalinity (unpublished) • BT article on Chloramine • New York Times Science article (geology and beer). • 54 recipes for water of various brewing cities from common salts and distilled water.

  10. Part 0Overview - Beer and Water

  11. Water and Beer Style • Water is heavy (1 kg/L ~ 8.3 Lbs/gal.) • Barley, malt and hops can be cost effectively moved fairly long distances - water can not. • Therefore, absent ability to treat it, local water determined what local beer was like • Soft water: Bohemian Pils • Hard, bicarbonate Water: Munich Dunkles, London Ales • Remove bicarbonate and you can make Helles • Hard Sulfate Water: Burton Ales

  12. The First of the Two Aspects • Bicarbonate is a base - it’s alkaline • It raises mash pH ~ malt enzymes become less effective • It must be neutralized or removed (so pH is kept low) • Hardness (Ca++, Mg++) plus malt phosphate neutralize it • Alkalinity (water bicarbonate) not neutralized by water hardness + malt phosphate is called Residual Alkalinty • Acid neutralizes it • Sulfuric, hydrochloric, lactic, acid in dark malt • High alkalinity water requires lots of hardness, acid and or dark malt to neutralize it (and conversely) • Theme: Contest between alkalinity (bad) and hardness (good) for control of mash pH.

  13. Hardness & Alkalinity for Several Cities Bad OK Good OK RA = Alkalinity - (Ca_hardness + Mg_hardness/2)/3.5

  14. Part 1 Fundamentals of Chemistry:Atoms, Molecules, Ions, Acids, Bases

  15. For Further Information… • We can only skim (rapidly) the surface at the highest level today • Nothing here beyond college freshman chemistry • Should today stimulate your interest, review freshman chemistry or biochemistry text • Pay particular attention to ionic equilibrium (law of mass action), acid/base chemistry, Henderson Hasselbalch equation. • Read Cerevesia article on CD

  16. Atoms • Smallest particle of elemental matter with nucleus of positively charged protons and uncharged neutrons… • … of mass ~1.673E-24 grams (protons and neutrons slightly different) • Surrounded by negatively charged electrons • With mass 0.000911E-24 grams (1/1822 of proton) • Number of electrons equals number of protons • Atom has a net charge of 0. • Electrons group into shells • Most of the elements we’ll deal with like to have 8 electrons in outer shell • The number of protons (and electrons) determine which element the atom is • 1: H, 2: He, 3: Li, 4: Be, 5: B, 6: C 7: N, 8: O 9: F, 10: Ne • Number of neutrons determines which isotope • 6 protons + 6 neutrons ~ 12C (normal); 6p + 8n ~ 14C (radioactive)

  17. Chemical Symbols • Each element (atom type) is represented by a symbol • It’s often pretty obvious which element is meant… • H ~ Hydrogen C ~ Carbon O ~ Oxygen Ca ~ Calcium Mg ~ Magnesium S ~ Sulfur • But not always… • Na ~ Sodium (L. Natrium) K ~ Potassium (L. Kalium) Fe ~ Iron (L. Ferrum) Hg ~ Mercury (L. Hydrargyrum) • Combined atom symbols represent compounds: • NaCl ~ Sodium chloride HCl ~ Hydrochloric Acid CaCl2 ~ Calcium chloride H2CO3 ~ Carbonic acid CaCO3 ~ Calcium Carbonate CaSO4.2H2O Calcium Sulfate with 2 waters of hydration. • Subscript indicates number of atoms in molecule • 1 Molecule of CaCO3 has 1 calcium, 1 Carbon, 3 Oxygen atoms • Ion (electrically charged atom or molecule) is indicated by element or compound symbols with charge shown • Na+ ~ Sodium ion Ca++ ~ Calcium ion HCO3- ~ Bicarbonate

  18. IONS • Noble gasses Helium, Neon, Argon… have complete electron shells ~ chemically stable • Atoms may take on or release electrons to complete or leave a complete shell • Sodium ([Ne]+1e-): Na --> e- + Na+ Sodium Ion • [Noble gas] represents the electronic structure of that gas • Giving up 1 electron leaves Neon (10 e-) shell structure • Could give it to e.g. chlorine… • Chlorine ([Ne]+7e-): Cl + e- --> Cl- Ion • ([Ne]+8e- = [Ar]) • Calcium ([Ar]+2e-): Ca --> 2e- + Ca++ Ion • Take away 2 electrons leaves Argon shell structure • Hydrogen (1 e-): H --> e- + H+ Hydrogen Ion • Naked proton (quickly attaches to a water molecule)

  19. Molecules • Atoms can also share (or give) electrons with (to) other atoms in order to complete shells • Carbon (C) has 4 electrons in its outer shell: [He]+4e- • Hydrogen (H) has 1 electron: 1e- • If carbon shares the electrons from each of 4 hydrogen atoms it completes its outer (valence) shell : • [He] + 4e- + 4e-(shared from hydrogens) ~ [Ne] • Each hydrogen shares one of carbon’s electrons • 1e- + 1e- (shared from carbon) ~ [He] • CH4 is the gas methane • Na gives e- to Cl. Na+ attracts Cl- --> NaCl • Atoms so combined are called molecules the constituents of compounds.

  20. Dissociation • Some molecules (acids) may release or take on (bases) protons (hydrogen ions) thus becoming ions themselves • Carbonic Acid: H2CO3 --> H+ + HCO3- Bicarbonate ion • Ammonia (base): NH3 + H+ --> NH4+ Ammonium ion • Sulfuric Acid: H2SO4 --> H+ + HSO4- Bisulfate ion • Hydrochloric Acid: HCl --> H+ + Cl- Chloride ion • Ions can do this too and become doubly ionized or un-ionized • Bicarbonate ion: HCO3- --> H+ + CO3-- Carbonate ion • Bicarbonate ion: HCO3- + H+ --> + H2CO3Carbonic acid • Molecules (or ions) which give up protons are acids in the Lowry-Brønstead sense (there are other definitions) • Molecules (or ions) which take up protons are bases in the Lowry-Brønstead sense.

  21. Chemical Equations • Reactants on left, products on right • Equation in the sense that numbers of atoms (of each type) and charges must be equal on each side • Ca(OH)2 + Ca++ + 2HCO3- --> 2CaCO3 + 2H2O • This says that 1 molecule of calcium hydroxide (slaked lime) reacts with 1 calcium ion and 2 bicarbonate ions producing 2 molecules of calcium carbonate (chalk) which precipitates (underbar) and 2 molecules of water • 2 Calcium, 2 Carbon, 8 Oxygen, 4 Hydrogen, 0 charge on each side • --> indicates that reaction proceeds from left to right but not in other direction (many, indeed all, reactions proceed in both directions if conditions are right but one is sometimes preferred.) • This reaction is commonly used by brewers to remove bicarbonate from alkaline water. • Because it removes calcium, a component of hardness, as well it is usually thought of as a “water softening” treatment.

  22. Measurement of Chemicals • RE last slide: each molecule of lime will remove 2 bicarbonate ions. How much lime do we need to buy to process x gallons of water? • Clearly we need to have some idea of what a molecule weighs and how many we need. • Molecules, like atoms and ions, are made up of protons and neutrons which contribute nearly all the weight as electron weight is negligible • One proton weighs 1 Dalton (1 Atomic Mass Unit) • How many protons weigh one gram? • Answer: 6.023E+23 called Avogadro’s Number. • Avogadro’s number of Daltons = 1 gram • Avogadro’s number of anything (atoms, molecules, ions, electrons, rutabagas, even furry blind subterranean mammals) is called one mole

  23. Gram Molecular Weights ~Weight of 1 mole • Hydrogen: 1 proton. 1 mole should weigh about 1 gram. Actual GMW 1.00794 • Oxygen: 8 protons, 8 neutrons. 1 mole should weigh about 16 grams. Actual value 15.9994 • Calcium: 20 protons, 20 neutrons. 1 mole should weigh about 40 grams. Actual value 40.078 • Ca(OH)2: 38 protons, 38 neutrons. 1 mole should weigh about 74 grams. Actual GMW 74.093 • HCO3-: 31 protons, 30 neutrons. 1 mole should weigh about 61 grams. Actual GMW 61.03 • Thus 1 molecule of Ca(OH)2 reacting with 2 HCO3- ions implies that 6.023E23 (1 mole = 74.093grams) of Ca(OH)2 will react with 12.046E23 (2 moles = 122.06 grams) of HCO3- and so on in that proportion • Example: To decarbonate water with 61 milligrams (mg) of bicarbonate (1 millimole) per liter would require 1/2 mMol of Ca(OH)2 weighing 74.093/2 = 37.046 mg per liter.

  24. Equivalent Weight • Sometimes specified weights are based on moles of charge rather than moles of ions or atoms • Singly charged HCO3-: 31 protons, 30 neutrons. GMW 61.03 means 61.03 grams has a charge of 1 mole of (-) charges. Equivalent weight = 61.03. • Doubly charged Ca++: 20 protons, 20 neutrons. GMW 40.078 means 40.078 grams carries 2 moles of (+) charge. 20.039 grams carries 1 mole. Equivalent weight = 20.039 • Equivalent weight = gram molecular weight divided by charge. • Alkalinity (HCO3-) and hardness (Ca++, Mg++) are often expressed in milliequivalents per liter (mEq/L sometimes called mVal/L or just mVal). • Sometimes given as 50 times mEq/L - called parts per million as CaCO3 • This is seen a lot. Note: 1 ppm ~ 1 mg/L (as water weighs ~ 1 kg/L) 100mg 1mMol 44mg 1mMol 18mg 1mMol 122mg 2mMol 40mg 1mMol CaCO3 + CO2 + H20 --> 2HCO3- + Ca++ 2mEq 100ppm as CaCO3 2mEq 100ppm as CaCO3

  25. Example of Calculation • Being an environmentally conscientious brewer you wish to neutralize your standard lye cleaning solution (1 pound lye in 5 gal water) before dumping it down the drain. How much acid is needed? • Na(OH) + H2O --> Na+ +(OH)- + H2O • Lye GMW 40: 1 lb = 454 g ~ 454/40 = 11.36 Mol ~ 11.36 Eq (OH)- • H+ + (OH)- --> H2O Need 11.36 Eq H+ • Sulfuric Acid MW 98: H2SO4 --> 2H+ + SO4-- • 11.36/2 Mol H2SO4 yields 11.36 Eq H+ • 98*11.36/2 = 556 grams ~ 1.23 lbs concentrated sulfuric acid required. • 11.36 Mol of Na+ & 11.36/2 Mol SO4-- (11.36/2 Mol Na2SO4, MW 142 ~ 11.36*142/2 = 0.806 kg) go down drain (wrong on CD) • Hydrochloric Acid MW 36.46: HCl --> H+ + Cl- • 38% HCl solution (23 Baume) is 12.29 Normal meaning it contains 12.29 Eq H+ per litre. Therefore need 11.36/12.29 = 0.917 L of 38% HCl • 664 g NaCl (table salt) goes down drain • Add acid to solution until pH neutral rather than relying on calculation

  26. Another Example Calculation • Water tests 3 mg/L available chlorine (from chloramine). How much potassium metabisulfite (K2S2O5 MW 222.32) is required to treat 20 gal (76 L) • 2K+ + S2O5-- + 2H2NCl + 3H2O --> 2K+ + 2SO4-- + 2H+ + 2Cl- + 2NH4+ • Each mole of chlorine requires 0.5 mole of bisulfite ion and produces 1 mole of sulfate, 1 equivalent of hydrogen ions, 1 mole of chloride ions and 1 mole of ammonium ions. • 3 mg/L Cl ~ 3/35.45 = 0.0846 mMol/L requiring 0.0423 mMol/L metabisulfite and producing 0.0846 mMol/L sulfate, hydrogen, chloride and ammonium ions. • The GMW of potassium metabisulfite is 222.32 mg/mMol so we need 9.4 mg/L or 714 mg total (one lot of Campden tablest we measured weighed 695 mg) • The hydrogen ions, 0.0846 mEq/L represent a reduction in alkalinity of 50 times this or 4.2 ppm as CaCO3. • As each bound chlorine atom is converted to a chloride ion the chloride level will increase by 3 mg/L • 0.0846 mMol/L * 96 mg/mMol ~ 8.12 mg/L increase in sulfate (Pils brewers take note) • 0.0846 mMol/L*18 mg/mMol ~ 1.5 mg/L increase in ammonium ion (your yeast will love it)

  27. Part 2Carbon Dioxide, Water & Limestone; Hardness & Alkalinity

  28. Carbon Dioxide: CO2 MW 44.01 light • Spewed by volcanoes • Taken up by plants -> sugar, starch… oxygen • 6CO2 + 6H2O ------> C6H12O6 + 6O2 • Released by carbohydrate oxidation (including respiration, fermentation, decay…) • CnH2nOn + nO2 --> nCO2 + nH2O • A greenhouse gas • Though not a very effective one (10% re water vapor) • Present in the atmosphere to the extent of 0.03% (0.0003Atm ~ 0.3 hPa) • Absorbed/released by oceans, rivers, lakes • Sequestered by animals which build shells from it • Dissolves in water to form carbonic acid which, in turn, dissolves limestone • This is the property of significance to brewers (and spelunkers).

  29. Water • Continuous cycle of evaporation, condensation, precipitation… • Ultimately comes to us from rain, snow, meltoff.. • Runs over surface of earth into a stream/pond… • In equilibrium with atmospheric CO2 • Leaches substances from surface organic/inorganic materials with which it comes in contact • Or percolates into ground and is withdrawn from well penetrating aquifer • In equilibrium with subterranean CO2 (respiring bacteria) • Typically more acidic (dissolved CO2) • Dissolves minerals from rock with which it comes in contact • Limestone caves • Typically more mineral content than surface water • Usually clearer, fewer bacteria than surface (well filtered) • May be in the ground for years.

  30. Carbonic Acid MW 62.03 • CO2 dissolves in water to form carbonic acid… • CO2 + H2O <--> H2CO3* • * indicates this is both dissolved but not hydrated CO2 and hydrated CO2 • Arrow is two headed. Carbonic acid can decompose into water and CO2 • … which can give up a proton to form bicarbonate ion… • H2CO3* <--> H+ + HCO3- • Ability to give up proton defines H2CO3 as an acid • In reverse, HCO3- can take up a proton to form H2CO3. This defines a base • …which can give up its proton to form carbonate… • HCO3- <--> H+ + CO3-- • The fact that it does so defines bicarbonate as an acid. • Thus bicarbonate is an acid and a base (it is amphoteric) • Which it behaves as depends on pH (at brewing pH it is basic) • In reverse, CO3-- takes up a proton to form HCO3-. CO3-- is a base • …which can coalesce with calcium ion to precipitate chalk • CO3-- + Ca++ <--> CaCO3 (only slightly soluble)

  31. Calcium Carbonate MW 100.087 • Ca++ + CO3-- --> CaCO3 (lime, chalk, limestone) • Happens in the bodies of marine animals • Main source of limestone - sequesters CO2, sends to bottom • 10% of all sedimentary rock • Happens when hard bicarbonate water is heated • Popular method for decarbonating brewing water • Or when hard bicarbonate water evaporates • Shower heads • Stalactites/Stalagmites • Dissolved by carbonic acid - source of calcium hardness • CaCO3 + H2O + CO2 --> CaCO3 + H2CO3 --> 2HCO3- + Ca++ • Surface and ground water are hard & alkaline • Cave formation: underground paCO2 much higher (hence more carbonic) because of respiring bacteria

  32. Law of Mass Action • In any reaction mA + nB <--> kC + jD • {C}k{D}j/{A}m{B}n = K, a constant (constant temp.) • {A} = activity of A • For a gas {A} is approximately the partial pressure • For a dissolved substance {A} is approximately the concentration (moles per liter) • For a solid {A} = 1 • Define p{A} = - log10{A} • Then kp{C} + jp{D} - mp{A} - np{B} = pK • If A + B <--> C (underscore ~ precipitation) then • {A}{B} < Ks (solubility product) No precipitation occurs • {A}{B} > Ks supersaturated. Precipitation usually occurs • {A}{B} = Ks saturated. No precipitation • p{A} + p{B} = pKs at saturation

  33. Carbonic - Loss of 1st Proton • H2CO3* <--> H+ + HCO3- • {H+}{HCO3-}/{H2CO3*} = K1 • pH + p{HCO3-} - p{H2CO3*} = pK1 • Henderson-Hasselbalch Equation • p{x} = - log x • p{H+} = pH is special - more to follow on this • pH - pK1 = p{H2CO3*}- p{HCO3-} • rearranged • 10 pH - pK1 =10p{H2CO3*} - p{HCO3-} = {HCO3-} / {H2CO3*} = r1 = ratio bicarbonate to carbonic • Took antilog of both sides • Note if pH = pK1then r1 = 1; {HCO3-} = {H2CO3*}

  34. Carbonic - Loss of 2nd Proton • HCO3- <--> H+ + CO3-- • {H+}{CO3--}/{HCO3-} = K2 • pH + p{CO3--} - p{HCO3-} = pK2 • pH - pK2 = p{HCO3-}- p{CO3--} • 10 pH - pK2 =10p{HCO3-} - p{CO3--} = {CO3--} / {HCO3-} = r2 = ratio carbonate to bicarbonate • If pH = pK2 then r2 = 1; {CO3--} = {HCO3-} • Solutions tend to resist pH changes near their pK’s • This is called buffering

  35. H2CO3, HCO3-, CO3-- Fractions • If there are x moles of carbonic, there are r1x moles of bicarbonate and xr1r2 moles of carbonate for a total of CT = x(1 + r1 + r1r2) =xd • CT = total carbo • The fraction which is carbonic is x/xd = 1/d = f1 • The fraction which is bicarbonate is r1 times this = r1/d = f2 • The fraction which is carbonate is r2 times this or r1r2d = f3

  36. Distribution of carbo species pHs pK2 10.35 pK1 6.38 Alkalinityis defined as the number of mEq of acid required to change the pH of a sample from its pH at the source (pHs) to pH 4.3

  37. Alkalinity • Definition: the number of mEq of acid required to change pH of a sample to a reference pH (usually pHr = 4.3) • Sum of • Acid required to change carbonate to carbonic • Acid required to change bicarbonate to carbonic • Acid required to increase {H+} to (1000)10-pHr mEq/L • Acid require to neutralize (OH)- • r ~ reference pH, s ~ sample pH, pKw = 14 • Units: mEq/L (that’s why the factor of 1000 is there) • CT = total mmol/K carbonic, bicarbonate, carbonate • Equation can be solved for CT if alk, pHr and pHs are known • Thus choice of pHr is somewhat arbitrary alk = CT(f1,r - f1,s + f3,s- f3,r) + (1000)10(pHs-pHr) + (1000)10(pKw-pHr-pHs)

  38. Solubility Product • {Ca++}{CO3--}< KsSolubility Product • If {Ca++}{CO3--} = Ks water is called saturated • p{Ca++}+p{CO3--}< pKs • Calcium carbonate is not very soluble in water • To precipitate carbo (and hardness) establish conditions which violate inequality • Increase pH & thus f3 (Drive off CO2 by heat, sparge) • Decrease Ks (raise temperature) • Increase {Ca++} (add gypsum or CaCl2) • Combinations (Ca(OH)2 increases pH and {Ca++})

  39. Combine Equations • Add Eqns for dissolving CO2, CaCO3 saturation, water dissociation and electric neutrality • CO2 Dissolves: • A proton is lost: • A 2nd proton is lost: • CaCO3 Saturation: • Water dissociates: • The total charge is 0: • Define: • Substitute into charge neutrality equation, • Solve (root finder) for pH which satisfies this equation • Substitute back pfm accounts for fact that solutions are not “ideally dilute”. We will ignore this.

  40. Why All this Horrible Math? • It is what allows us to … • Validate a water analysis • Calculate alkalinity and estimate the acid required for proper mash pH • Synthesize any water ion profile from any starting water (e.g. salt additions to get Burton water from my well water) • Determine whether water is stable (saturated with respect to CO2 or CaCO3 • Make charts like one on next slide • It is what is behind the spreadsheet on the CD

  41. CO2 Over Water in Equilibrium with CaCO3

  42. Review - Dissolving Limestone Alkalinitycomes from limestone and the carbonic acid which Is required to dissolve it. Calcium hardness comes from dissolved limestone.

  43. pH • Søren Peter Lauritz Sørenson (1868 -1939) • Worked at Carlsberg Laboratory • Studied amino acids, proteins enzymes • Their behaviour (total electric charge) depends on hydrogen ion concentration (mechanism we’ve been discussing). • Sought convenient scale for specifying {H+} (1909) • Called it pondus (L. a weight) hydrogenii i.e. pH = -log10{H+} • For pure water {H+} = 10-7 Mol/L thus pH = 7 • For .001 N acid {H+} = 10-3 Mol/L thus pH = 3 • pH < 7: Acid, sour, beer, wine, soda (phosphates), vinegar, lemon, lime (citrus), sauerkraut, sour cream, kimche • pH ~ 7: Neutral, water, blood, brine • pH > 7: Base, bitter, lye, lime (slaked), soda ash

  44. H+ H+ H3N+CRHCOOH H3N+CRHCOO- H2NCRHCOO- pH 1 Q = 1 pH 6 Q = 0 pH 14 Q = -1 Importance of pH in Brewing • Necessary to calculate carbo species distribution in water • As pH changes charge distribution on proteins it changes conformation of enzymes • Brewing water treatment is done to get enzymes properly conformed for protein lysis, starch to sugar conversion… • Happens in range pH 5.2-5.7 • Proper charge distribution on proteins (chains of amino acids) in boil (iso-electric point~ net charge 0) enhances coagulation Charge (Q) shown for simplest amino acid, Glycine (R = H) Note: For some amino acids (Arginine, Lysine, Tyrosine….) R may be ionizeable in which case other charge values are possible

  45. Importance of pH II • Tanins not extracted from barley husks if sparge pH < 6 • Yeast produce acid to kill competing organisms • Thus pH drop is first sign of healthy fermentation • pH has an effect on stability of colloids in finished beer. • pH modulates formation of melanoidins • IOW, each part of the brewing process proceeds best in a range of pH (and temperature) • XI DeClerck Chair: 3 Days of lectures on “pH Paradox” devoted to this subject • Advanced brewer feels as helpless without his pH meter as he does without his thermometer.

  46. pH Measurement • Originally with dye which changes color at particular pH • “Litmus Test” from a lichen (red < 7, blue >7) • Phenolpthalein, bromcresol red, methyl orange (4.3) … • Electronically: potential developed across specially prepared (delicate) glass bulb dependent on pH difference between inside and out • Potential measured between electrode inside bulb and reference junction electrically connected to solution being measured (outside bulb) • Very feeble current. Extremely high impedance amplifier required • 57 millivolt change per unit pH change • Depends on temperature - temperature compensation essential • Note: pH also changes with temperature (because pK’s do). This is a separate effect • Special field effect transistors (ISFET) • Much more durable, store dry • Modern meters more dependable, last longer, less expensive, feature rich (ATC, auto buffer recognition) but still not for the casual user. • Must be calibrated frequently with buffers of known pH

  47. Part IIIAdding Phosphate, Residual Alkalinity

  48. Phosphoric Acid Chemistry • Same as carbonic except • The oxide is a solid: P2O5 + 3H2O --> 2H3PO4 • Compare: CO2 + H2O --> H2CO3 • General reaction for oxoacids • Includes carbonic, phosphoric, nitric, sulfuric • Three protons: • H3PO4 --> H+ + H2PO4- --> 2H+ + HPO4-- --> 3H+ + PO4--- • Three (not the same as carbonic) pK’s (2.12, 7.21, 12.67), three r’s, three f’s. • Calcium phosphate is very insoluble • The smallest amount of phosphate will pull out lots of calcium • This is why trisodium phosphate was used as water softener • 3Ca++ + 2Na3PO4 ---> Ca3(PO4)2 + 6Na+ • And why malt phosphate lowers pH of hard water • Net reaction releases protons (hydrogen ions) - later slide

  49. Phytic Acid from Malt

  50. Malt Phosphate • Up to 2% of malt weight is phosphate • In the form of phytin, salt of myoinositol hexaphosphate • Enzyme phytase breaks down phytin releasing inorganic phosphate (H2PO4-, HPO4--) and B vitamin myoinositol (good for yeast) • Phytase survives only mild kilning i.e. active in pale base malts only • Phosphate coalesces with any calcium in water, precipitates and releases protons which lower mash pH. • Paul Kohlbach observed that 3.5 mEq of Ca++ or 7 mEq Mg++ “neutralize” 1 mEq alkalinity • Neutralize here means that the pH of a mash with all alkalinity neutralized has same pH as a distilled water mash (~ 5.7) • Defined Residual Alkalinity: RA = alk. -({Ca++} + {Mg++}/2)/3.5 • Alkalinity, hardnesses and residual alkalinity all in units of either mEq/L or ppm as CaCO3. • Also noted 0.085 pH shift for each mEq/L (50 ppm) of RA