Difference between revisions of "Titratable Acidity"

Revision as of 23:01, 15 September 2016

Titratable Acidity (abbreviated as TA) is an approximation of the Total Acidity of a solution, and has long been used in the production of wine. It is usually expressed in units of grams per liter (g/L), although other formats are also used ^[1]. Titratable Acidity is often mistakenly confused with Total Acidity, but they are not the same thing ^[2]. While Total Acidity is a more accurate measurement of the total acid content of a solution, Titratable Acidity is used because it is easier to measure. Although titratable acidity does not measure all acids, TA is generally considered a better way to measure perceivable acidity in sour beer and wine than pH ^[3].

TA versus pH

Many sour beer producers use pH to help determine how "sour" their beer is in relation to a set goal, previous batches, or commercial examples. However, often times TA is a more accurate measurement of how acidic a beer will be perceived on the palate.

pH

In chemistry, pH is the negative log of the activity of the hydrogen ion (H+) in an aqueous solution. Solutions with a pH less than 7 are said to be acidic and solutions with a pH greater than 7 are basic or alkaline. Pure water has a pH of 7.

The pH scale is traceable to a set of standard solutions whose pH is established by international agreement ^[4]. Primary pH standard values are determined using a concentration cell with transference, by measuring the potential difference between a hydrogen electrode and a standard electrode such as the silver chloride electrode. Measurement of pH for aqueous solutions can be done with a glass electrode and a pH meter, or using indicators.

pH measurements are important in medicine, biology, chemistry, agriculture, forestry, food science, environmental science, oceanography, civil engineering, chemical engineering, nutrition, water treatment & water purification, and many other applications ^[4].

pH is best tested in sour beers using a PH Meter and is most useful for biological parameters. Microbial growth, vitality, and death are evaluated based on pH rather than TA. This means pH should be used when testing sanitizer, Wort Souring, starter cultures, etc.

TA

Titration is an attempt to quantify an unknown substance with a known one. Titratable acidity asks how much of a given base (in our case sodium hydroxide, NaOH) neutralizes the acid(s) (lactic, phosphoric, etc) in a volume of liquid. The units of TA can be quoted in g/L, or in other words, so many grams (of a specific acid) in so much substrate (beer) brings the pH of that substrate to a predetermined pH (for instance, a pH of 7 or 8.2).

Titratable acidity does not target a specific acid in the liquid you are measuring. Beer is composed of lactic acid, but also phosphoric acid, acetic acid, etc. While the latter are in minute quantities, they still affect the end result. For our purposes (and convention), we assume 100% lactic acid in the sample for our titration.

Why care about titratable acidity? pH quantifies the number of hydrogen ions (or hydrogen ion equivalents) in liquid. Your palette does not measure pH directly. Your palette interprets a multi-variable substrate called beer. Titratable acidity attempts to put another quantifiable handle on your beer akin to pH; the measurement better captures how “acidic” the beer may taste to you. Again, there are other acids than lactic in the beer, leading to differences in flavor between beers of the same TA.

Titratable acidity can be expressed in terms of different acids. In wine, TA is generally expressed in terms of tartaric acid (molecular weight of 150.09). In sour beer, TA is expressed in terms of lactic acid (molecular weight 90.08). To express TA in terms of a specific acid, the molecular weight of the specified acid is used in the TA calculation. In the example below, we lactic acid to express the TA value. See appendix 1 in this paper on how to convert the titratable acidity value for different acids. Note that this is NOT a measurement of how much lactic acid or tartaric acid there is, it is an expression of measurement like how feet and meters are two different expressions of measurement for the same thing (distance). For example, a TA of 3.0 measured in units of tartaric acid is equal to a TA 3.6009 measured in units of lactic acid. Therefore, an argument can be made that TA measurements should always be specified as to which acid was used in the calculation.

Example

"I agree that maths are hard." - Lance Shaner.

What you will need:

A reliable and calibrated PH Meter.

Sample of beer to be measured. Must be fully degassed if it has any carbonation (pour through a coffee filter, or shake and ventilate to decarbonate).

Sodium Hydroxide, NaOH. Available in liquid or powder form. Be sure to note its molarity (M), units of mol/L. For more info on mol, see here.

Safety caution: always wear safety glasses and gloves when handling NaOH in any concentration.  NaOH can cause severe burns.  In concentrations higher than 0.1, NaOH can corrode through clothing.  See Canadian Centre for Occupational Health and Safety on Sodium Hydroxide.

Nitrile or latex gloves. NaOH is a strong base, it will hurt you if you get any on your skin.

Pipettes and glassware, with precision down to 0.1 mL. Alternatively, you can use a precision scale to dose the base into the beer, if you know the density of both liquids (preferred method).

We need a precise volume of the beer. In this case, we have 15 mL. We also need NaOH in liquid form. Typically, it is sold in 0.1M form. Now, the trickiest part of this is adding precise amounts of NaOH (say, 0.1-0.5 mL at time), to your 15 mL of beer. Every time you add NaOH, you must vigorously stir the sample so it is well-mixed. Then you can measure its pH. You continue this until you reach the desired pH baseline of 8.2. (Note: The baseline value of 8.2 pH is somewhat arbitrary, but it is the US and Australian industry standard. A pH of 7 is a neutral pH and the pH of water, whereas ~8.2 is near the equivalence point for a lactic acid/sodium hydroxide reaction. A pH of 8.2 is also where a titration dye, phenolphthalein, changes color. A well-calibrated pH meter is easier to use than dye, not to mention its superior accuracy and precision, if used correctly (well-calibrated, probe well-maintained, etc). A pH of 7 is the European industry standard for measuring TA in wine ^[5].

At or around a pH of 8.2, we have reached our equivalence point for a titration of pure NaOH and pure lactic acid. We need to convert the moles of NaOH we added into moles of lactic acid, and then divide the equivalent grams of lactic acid by the original volume of beer. That gets us g/L, and our titratable acidity. For a numerical example, assume 15mL beer, 5mL 0.1M NaOH:

The Eccentric Beekeeper TA Spreadsheet calculates TA as well as blends of beers with different TA values. It also includes a correction for beer final gravity. The idea is that the more residual sugar there is the less effect the acid will have on your perception. This is likely not that straightforward since you can have varying levels of sweetness at the same given FG ^[6].

In summary, the measurement of titratable acidity is technique to quantify the total acid level of a beer. A major assumption was made: all the acid in the liquid was lactic acid. Two beers could have the same TA measurement, but have differing levels of palatable acidity, due to the acid makeup of the beer.

Videos

Titration of a weak acid with a strong base by Kahn Acadmey part 1:

Part 2:

Measuring Titratable Acidity in Wine (use the calculation above instead of the calculation in the video to express the value in terms of lactic acid):

Authorship

Originally written by James Howat with major updates by Andy Carter, and with input from Dan Pixley and Mike Castagno.

References

[1] Wine From the Outside - Easy Wine Chemistry For the Casual Chemist. Monitoring Acids and pH in Winemaking. Mike Miller.

[2] The relationship between total acidity, titratable acidity and pH in wine. Roger Boulton. American Journal of Enology and Viticulture. 31(1): 76-80. 1980.

[3] How Sour is Your Sour Beer?. OCBeerBlog on Firestone Walker's demonstration of the uses of TA measurements. April 13, 2015.

[bates-4] 4.0 ^4.1 Bates, Roger G. Determination of pH: theory and practice. Wiley, 1973.

[5] "TN14 - Interconversion of acidity units" Industry Development and Support. Australian Wine Research Institute. Retrieved 09/15/2016.

[6] Conversation with Dave Janssen on MTF. 6/23/2015.

[1]

[2]

[3]

[4]

[5]

[6]

@@ Line 1: / Line 1: @@
-'''Titratable Acidity''' (abbreviated as '''TA''') is an approximation of the ''Total Acidity'' of a solution, and has long been used in the production of wine.  It is usually expressed in units of grams per liter (g/L), although other formats are also used <ref>[http://www.accuvin.com/wp-content/uploads/2015/04/Monitoring-Acids-and-pH-in-Winemaking.pdf Wine From the Outside - Easy Wine Chemistry For the Casual Chemist.  Monitoring Acids and pH in Winemaking.  Mike Miller.]</ref>.  Titratable Acidity is often mistakenly confused with Total Acidity, but they are not the same thing (see reference).  While Total Acidity is a more accurate measurement of the total acid content of a solution, Titratable Acidity is usually used because it is easier to measure <ref>[http://wineserver.ucdavis.edu/pdf/attachment/220%20relationship%20between%20total%20acidity,%20TA,%20and%20pH%20.pdf The relationship between total acidity, titratable acidity and pH in wine.  Roger Boulton.  American Journa l of Enology and Viticulture. 31(1): 76-80. 1980.]</ref>.  TA is generally considered a better way to measure perceivable acidity in sour beer and wine than pH <ref>[http://blog.ocbeerblog.com/2015/04/13/how-sour-is-your-sour-beer/ How Sour is Your Sour Beer?.  OCBeerBlog on Firestone Walker's demonstration of the uses of TA measurements.  April 13, 2015.]</ref>.
+'''Titratable Acidity''' (abbreviated as '''TA''') is an approximation of the ''Total Acidity'' of a solution, and has long been used in the production of wine.  It is usually expressed in units of grams per liter (g/L), although other formats are also used <ref>[http://www.accuvin.com/wp-content/uploads/2015/04/Monitoring-Acids-and-pH-in-Winemaking.pdf Wine From the Outside - Easy Wine Chemistry For the Casual Chemist.  Monitoring Acids and pH in Winemaking.  Mike Miller.]</ref>.  Titratable Acidity is often mistakenly confused with Total Acidity, but they are not the same thing <ref>[http://wineserver.ucdavis.edu/pdf/attachment/220%20relationship%20between%20total%20acidity,%20TA,%20and%20pH%20.pdf The relationship between total acidity, titratable acidity and pH in wine.  Roger Boulton.  American Journal of Enology and Viticulture. 31(1): 76-80. 1980.]</ref>. While Total Acidity is a more accurate measurement of the total acid content of a solution, Titratable Acidity is used because it is easier to measure.  Although titratable acidity does not measure all acids, TA is generally considered a better way to measure perceivable acidity in sour beer and wine than pH <ref>[http://blog.ocbeerblog.com/2015/04/13/how-sour-is-your-sour-beer/ How Sour is Your Sour Beer?.  OCBeerBlog on Firestone Walker's demonstration of the uses of TA measurements.  April 13, 2015.]</ref>.
 ==TA versus pH==
@@ Line 11: / Line 11: @@
 pH measurements are important in medicine, biology, chemistry, agriculture, forestry, food science, environmental science, oceanography, civil engineering, chemical engineering, nutrition, water treatment & water purification, and many other applications <ref name="bates"></ref>.
-pH is best tested in sour beers using a [[PH Meter]] and is most useful for biological parameters. Cells live or die based on pH, not TA. This means pH should be used when testing sanitizer, sour worting, starter cultures, etc.
+pH is best tested in sour beers using a [[PH Meter]] and is most useful for biological parameters. Microbial growth, vitality, and death are evaluated based on pH rather than TA. This means pH should be used when testing sanitizer, [[Wort Souring]], starter cultures, etc.
-===Why TA?===
+===TA===
-When attempting to use pH for sensory parameters (how sour something tastes), the measurement falls short. Humans perceive acidity from tasting acids rather than the dissociated H+ ions which determine pH. With strong acids, where the H+ ions are fully dissociated from the remaining acid molecules, the amount of acid is always equal to the amount of H+ ions. However, lactic acid, the primary acid in sour beer, is a weak acid. Weak acids do not completely ionize/dissociate, leaving some portion of the H+ still bound to the acid. The degree to which a weak acid dissociates depends on the identity of the acid and the composition of the solution it is in.
+Titration is an attempt to quantify an unknown substance with a known one. Titratable acidity asks how much of a given base (in our case sodium hydroxide, NaOH) neutralizes the acid(s) (lactic, phosphoric, etc) in a volume of liquid. The units of TA can be quoted in g/L, or in other words, so many grams (of a specific acid) in so much substrate (beer) brings the pH of that substrate to a predetermined pH (for instance, a pH of 7 or 8.2).
-Any acid not dissociated (in other words, an acid still holding onto its H+) does not affect pH. On the other hand, humans will perceive an increased "sourness" based upon the amount of acid in a beer, dissociated or not. The best way to test for total acidity, regardless of dissociation, is using a test called Titratable Acidity. Because different acids have different characteristic flavors and some acids might taste more smooth or aggressive than others (think lactic acid verses acetic acid), samples with the same titratable acidity may have either different perceived acidity or acidity that seems more or less pleasant than other samples. However overall titratable acidity does show a stronger correlation to perceived acidity than measures such as pH.
+Titratable acidity does not target a specific acid in the liquid you are measuring. Beer is composed of lactic acid, but also phosphoric acid, acetic acid, etc. While the latter are in minute quantities, they still affect the end result. For our purposes (and convention), we assume 100% lactic acid in the sample for our titration.
-Kara Taylor at White Labs has done a reasonable amount of professional sensory panels showing the correlation between TA and perceived sour taste, as well as showing a more poor correlation between pH and sour taste. Her full presentation, where most of this information was sourced, is available to any attendee of the 2015 Craft Brewer's Conference.
+Why care about titratable acidity? pH quantifies the number of hydrogen ions (or hydrogen ion equivalents) in liquid. Your palette does not measure pH directly. Your palette interprets a multi-variable substrate called beer. Titratable acidity attempts to put another quantifiable handle on your beer akin to pH; the measurement better captures how “acidic” the beer may taste to you. Again, there are other acids than lactic in the beer, leading to differences in flavor between beers of the same TA.
-==Testing for Titratable Acidity in Sour Beer==
+Titratable acidity can be expressed in terms of different acids.  In wine, TA is generally expressed in terms of tartaric acid (molecular weight of 150.09).  In sour beer, TA is expressed in terms of lactic acid (molecular weight 90.08).  To express TA in terms of a specific acid, the molecular weight of the specified acid is used in the TA calculation.  In the [[Titratable_Acidity_2#Example|example below]], we lactic acid to express the TA value.  See [http://www.awri.com.au/wp-content/uploads//TN14.pdf appendix 1 in this paper] on how to convert the titratable acidity value for different acids.  Note that this is NOT a measurement of how much lactic acid or tartaric acid there is, it is an expression of measurement like how feet and meters are two different expressions of measurement for the same thing (distance).  For example, a TA of 3.0 measured in units of tartaric acid is equal to a TA 3.6009 measured in units of lactic acid.  Therefore, an argument can be made that TA measurements should always be specified as to which acid was used in the calculation.
-''Safety caution: always wear safety glasses and gloves when handling NaOH in any concentration.  NaOH can cause severe burns.  In concentrations higher than 0.1, NaOH can corrode through clothing.  See [https://www.ccohs.ca/oshanswers/chemicals/chem_profiles/sodium_hydroxide.html Canadian Centre for Occupational Health and Safety on Sodium Hydroxide].''
-===Equipment Requirements:===
+===Example===
-# pH Meter with Automatic Temperature Correction
+''"I agree that maths are hard."'' - Lance Shaner.
-# Buffer/Testing Solutions for pH Meter
-# Buret (100mL recommended) with Stopcock
+What you will need:
-# Buret stand (can be DIY)
-# 250ml - 500ml Beaker (or pint glass, etc)
+* A reliable and calibrated [[PH Meter]].
-# 0.1N Sodium Hydroxide (NaOH - also labeled as ''0.1 M NaOH'')
-# Accurate way to measure 50mL (can use the buret for this, but I recommend a serological pipette or high-grade graduated cylinder)
-# Coffee filter or some other way to decarbonate beer (shake and vent repeatedly, pour through filter, etc)
-# Hydrometer
-===Procedure===
+* Sample of beer to be measured. Must be fully degassed if it has any carbonation (pour through a coffee filter, or shake and ventilate to decarbonate).
-# Calibrate the pH meter.
-# Pipette 50mL of decarbonated beer into the beaker.
-# Place the pH probe and the ATC thermometer into the beaker, submerge tip of the probe into the beer.
-# Fill the buret with 0.1N of NaOH.
-# Open the Stopcock and add the NaOH to the beer until pH meter reaches a reading of pH 7.0.
-# Upon reaching 7.0 pH, slowly add more NaOH until pH meter reads exactly pH 8.2, keeping track of how much NaOH is added.
-# Record the total amount of NaOH used to reach pH 8.2, including the amount that was needed to reach a pH of 7.0 and the additional amount needed to reach a pH of 8.2.
-# Use the following formula to find the ''Titratable Acidity'': '''Titratable Acidity = (mL 0.1N NaOH * 0.9) / (mL beer * Specific Gravity)'''
-# The number you get is ''percent TA'' (or ''grams/100mL TA'').
-# Multiply the ''percent TA'' by 10 to get ''g/L TA''.
-:''Note: Specific Gravity has a limited role in the equation.  For example, a change from an SG of 1.000 to 1.020 is only a change of 2%.  Final Gravity plays a large role in the perceived acidity due to the residual sugars balancing sourness on the palate.  Hence why Rodenbach, for example, has a less perceived sourness on the palate than its measurement of TA would indicate <ref>[https://www.facebook.com/groups/MilkTheFunk/permalink/1097532690274944/?comment_id=1097668506928029&offset=0&total_comments=19&comment_tracking=%7B%22tn%22%3A%22R5%22%7D Conversation with Dave Janssen on MTF.  6/23/2015.]</ref>.
-===Example===
+* Sodium Hydroxide, NaOH. Available in liquid or powder form. Be sure to note its molarity (M), units of mol/L. For more info on mol, see [https://en.wikipedia.org/wiki/Mole_(unit) here].
-''"I agree that maths are hard."'' - Lance Shaner.
+:<code>'''Safety caution''': always wear safety glasses and gloves when handling NaOH in any concentration.  NaOH can cause severe burns.  In concentrations higher than 0.1, NaOH can corrode through clothing.  See [https://www.ccohs.ca/oshanswers/chemicals/chem_profiles/sodium_hydroxide.html Canadian Centre for Occupational Health and Safety on Sodium Hydroxide].</code>
+* Nitrile or latex gloves. NaOH is a strong base, it will hurt you if you get any on your skin.
+* Pipettes and glassware, with precision down to 0.1 mL. Alternatively, you can use a precision scale to dose the base into the beer, if you know the density of both liquids (preferred method).
+We need a precise volume of the beer. In this case, we have 15 mL. We also need NaOH in liquid form. Typically, it is sold in 0.1M form. Now, the trickiest part of this is adding precise amounts of NaOH (say, 0.1-0.5 mL at time), to your 15 mL of beer. Every time you add NaOH, you must vigorously stir the sample so it is well-mixed. Then you can measure its pH. You continue this until you reach the desired pH baseline of 8.2. (''Note: The baseline value of 8.2 pH is somewhat arbitrary, but it is the US and Australian industry standard.  A pH of 7 is a neutral pH and the pH of water, whereas ~8.2 is near the equivalence point for a lactic acid/sodium hydroxide reaction. A pH of 8.2 is also where a titration dye, phenolphthalein, changes color. A well-calibrated pH meter is easier to use than dye, not to mention its superior accuracy and precision, if used correctly (well-calibrated, probe well-maintained, etc).  A pH of 7 is the European industry standard for measuring TA in wine <ref>[http://www.awri.com.au/wp-content/uploads//TN14.pdf "TN14 - Interconversion of acidity units"  Industry Development and Support.  Australian Wine Research Institute.  Retrieved 09/15/2016.]</ref>.''
+At or around a pH of 8.2, we have reached our equivalence point for a titration of pure NaOH and pure lactic acid.  We need to convert the moles of NaOH we added into moles of lactic acid, and then divide the equivalent grams of lactic acid by the original volume of beer. That gets us g/L, and our titratable acidity. For a numerical example, assume 15mL beer, 5mL 0.1M NaOH:
+[[File:TA_calc.PNG|center|800px|Titratable Acidity Example]]
+The [http://eccentricbeekeeper.com/spreadsheets/titratableacidity.xlsx Eccentric Beekeeper TA Spreadsheet] calculates TA as well as blends of beers with different TA values.  It also includes a correction for beer final gravity. The idea is that the more residual sugar there is the less effect the acid will have on your perception. This is likely not that straightforward since you can have varying levels of sweetness at the same given FG <ref>[https://www.facebook.com/groups/MilkTheFunk/permalink/1097532690274944/?comment_id=1097668506928029&offset=0&total_comments=19&comment_tracking=%7B%22tn%22%3A%22R5%22%7D Conversation with Dave Janssen on MTF.  6/23/2015.]</ref>.
+In summary, the measurement of titratable acidity is technique to quantify the total acid level of a beer. A major assumption was made: all the acid in the liquid was lactic acid. Two beers could have the same TA measurement, but have differing levels of palatable acidity, due to the acid makeup of the beer.
+==Videos==
+[https://www.khanacademy.org/science/chemistry/acid-base-equilibrium/titrations/v/titration-of-a-weak-acid-with-a-strong-base Titration of a weak acid with a strong base by Kahn Acadmey part 1:]
+<youtube>x3CbfUr449Y</youtube>
+[https://www.khanacademy.org/science/chemistry/acid-base-equilibrium/titrations/v/titration-of-a-weak-acid-with-a-strong-base-continued Part 2:]
-* Let's say we have 50 mL of mildly tart, uncarbonated beer.
+<youtube>WbDL7xN-Pn0</youtube>
-* It has a Specific Gravity of 1.010.
-* It took 12.2 mL of 0.1 N NaOH to get to a pH of 8.2.
-:''TA'' = (12.2 * 0.9) / (50 * 1.010)
-::= 10.98 / 50.5
-::= 0.217% ''TA'' (or 0.217 g/100mL ''TA'')
-::= 2.17 g/L ''TA''
-===Spreadsheet===
+Measuring Titratable Acidity in Wine (use the calculation above instead of the calculation in the video to express the value in terms of lactic acid):
-Milk The Funk member, "Eccentric Beekeeper", created the following spreadsheet to calculate TA, as well as calculating the TA of blends.  Download a copy to your computer to use it.
-* [http://eccentricbeekeeper.com/spreadsheets/titratableacidity.xlsx Eccentric Beekeeper Titratable Acidity Spreadsheet]
-==Uses in Sensory==
+<youtube>Im9U0-KaYaM</youtube>
-* It may be best to compare the ratio of Titratable Acidity to ''Final Gravity'' as sweetness counter-acts acidity in sensory experiments <ref>Kara Taylor, White Labs - CBC 2015 Presentation "Sour Beer is More than pH"</ref>.
-* [https://www.facebook.com/groups/MilkTheFunk/permalink/1211858545509024/ MTF discussion regarding Kara Taylor's BA presentation that shows TA for multiple beers, and suggestion for using "Sour Units" as a measurement for beer.]
 ==See Also==
@@ Line 71: / Line 67: @@
 ===External Resources===
+* [http://braukaiser.com/blog/blog/2010/11/25/wort-and-beer-titration/ Wort and Beer Titration by Kai Troester.]
 * More information on this procedure is available from the [http://www.asbcnet.org/Pages/default.aspx American Society of Brewing Chemists], who publish a similar set of procedures under the name "Total Acidity with Potentiometer".
 * [http://www.mbaa.com/districts/Northwest/mash/Documents/Acidity%20and%20Blending.pdf Jim Crooks of Firestone Walker presentation about blending sour beers using TA].
@@ Line 76: / Line 73: @@
 * [http://embracethefunk.com/ph-readings-of-commercial-beers/ pH Readings of Commercial Beers, Embrace the Funk Blog, Brandon Jones.]
 * [http://www.amazon.com/gp/product/B016AY7T76?colid=2U7JPR40PC5G2&coliid=I30J7IAENBH9DZ Amazon source for NaOH.]
+* [https://www.facebook.com/groups/MilkTheFunk/permalink/1211858545509024/ MTF discussion regarding Kara Taylor's BA presentation that shows TA for multiple beers, and suggestion for using "Sour Units" as a measurement for beer.]
 * [https://www.facebook.com/groups/MilkTheFunk/permalink/1204463789581833/ MTF tips on what type of NaOH to buy (liquid over dry), and how to handle it safely.]
 * [https://www.facebook.com/groups/MilkTheFunk/permalink/1228704607157751/?comment_id=1228977910463754&reply_comment_id=1228997810461764&comment_tracking=%7B%22tn%22%3A%22R7%22%7D MTF tips on safety and methods of measuring TA from a research technician.]
+==Authorship==
+Originally written by James Howat with major updates by Andy Carter, and with input from Dan Pixley and Mike Castagno.
 ==References==

Difference between revisions of "Titratable Acidity"

Revision as of 23:01, 15 September 2016

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TA versus pH

pH

TA

Example

Videos

See Also

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External Resources

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References

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