13,586
edits
Changes
updated TA example
* 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 and the specific gravity of the beer. If the specific gravity cannot be measured easily for some reason, then estimating it will be fine for this equation since small differences in specific gravity don't greatly impact the results of the equation. In this example, we have 15 mLwith a specific gravity of 1.015. 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 (ASBC<ref>[http://methods.asbcnet.org/summaries/beer-8.aspx ASBC Methods of Analysis. Total Acidity. Retrieved 11/8/2017.]</ref>) 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>. See also [https://www.facebook.com/groups/MilkTheFunk/permalink/1877187898976082/ this MTF thread].''
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 ''' beerwith a gravity of '''1.015''', '''5mL ''' 0.1M NaOH:
[[File:TA_calcTA example.PNGgif|center|800px500px|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>.