JUICE CHEMICAL ANALYSIS: WHAT TO MEASURE AND WHY

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1 JUICE CHEMICAL ANALYSIS: WHAT TO MEASURE AND WHY Anita Oberholster JULY 15, CURRENT ISSUES: FERMENTATION READINESS UC DAVIS CONFERENCE CENTER Anita Oberholster Introduction What to measure? How? When to measure? Why? What does it mean? 1

2 Brix 1Brix = 1 g of sugar per 100 g of solution Hydrometry or refractometer measures total soluble solids (90 94% sugars) Not analytical technique, only give estimation of amount of sugar Why measure? Indication of fruit ripeness Potential ethanol production in wine Yeast vary in their efficiency to convert sugar to alcohol could differ up to 0.8 % v/v Follow progress of fermentation Brix Why measure? Indication of fruit ripeness Potential ethanol production in wine Yeast vary in their efficiency to convert sugar to alcohol could differ up to 0.8 % v/v Conversion factor of Brix to EtOH Determine optimal yeast to use for fermentation Follow progress of fermentation 2

3 Brix adjustments Water back Grape concentrate Use Pearson s Square Vol of water/concentrate = V(D-A)/(C-D) V = vol juice D = desired Brix A = initial Brix C = Brix of water/concentrate Saignee Remember changing in some cases more than Brix, TA, ph, YAN Retest after any adjustments Brix adjustments Error in calculation Accuracy of Brix determination depends of homogeneity of grapes Influenced by grape ripeness Dehydrated and raisoned berries 3

4 Reducing sugars Mainly glucose and fructose Methods Rebelein method (titration with color change) Enzymatic analysis FTIR or winescan, HPLC (expensive) Why measure? Important for regulatory and wine style reasons, especially when aiming for specific sugar content ph Measure free H + ions ph = -log [H + ] Why is knowing the ph important? Microbial stability Effectiveness of SO 2 Molecular SO 2 is the form effective against microorganisms 4

5 ph Mouth-feel ( flabby ) wine style Color of red wine Red Colorless Yellow Blue Titratable acidity (TA) Measures concentration of all available hydrogen ions (both free and bound to dissociated acids (eg H 2 T) Tartaric and malic acid is the main organic acids present in grapes Citric acid is 3 rd most prevalent Rest formed during fermentation by yeast or bacteria 5

6 Titratable acidity (TA) How do you measure it? Titrating with known vol of NaOH to end point indicated by color change of indicator (ph 8.2) Expressed as g/l tartaric acid Foss, HPLC (measures individual acids) Titratable acidity (TA) Why is knowing the TA important? Guide to acid taste of wine Desired amounts depends on wine style Wine balance Adjust ph of juice/wine How much to add to adjust ph? Difficult to predict 6

7 Titratable acidity (TA) Adjust potential wine ph Change in ph not directly related to acid addition Depends on wine s buffer capacity Rule of thumb: 1 g/l of tartaric acid, decrease ph by 0.1 Efficiency of acidification can improve with CaSO 4 addition Add L(+)-tartaric acid DL-tartaric acid addition increase calcium tartrate instability De-acidify when ph <2.9 + TA > 10 g/l Add 1.3 g/l of KHCO 3 lower TA 1 g/l H 2 T Ion-exchange Malic acid Measure malic acid (and lactic acid) conc TLC, Enzymatic analysis, HPLC or FOSS Why measure? Chances of MLF MLF at ph<3 difficult Decrease TA with MLF 1 g/l malic acid, TA 0.56 g/l Following MLF T L M 7

8 Nitrogen (NH 3, NH 4+ and amino acids) Enzymatic analysis or HPLC, FTIR - MIR Why measure? N 2 deficiency Stuck fermentation Utilization of sulfur containing amino acids formation of H 2 S Too much N 2 Modify aroma character Formation of ethyl carbamate N 2 needed Depended on yeast needs and starting Brix Brix, need YAN (mg N/L) Nitrogen (NH 3, NH 4+ and amino acids) Yeast assimilable nitrogen (YAN) Ammonia (NH 3 ) and free alpha amino nitrogen (FAN) How to measure? Formol titration (FAN + NH 4+ ) Only need ph meter NOPA method (primary amino acids) Need Vis spectrophotometer Derivatization of primary amino acid groups with o- phthaldehyde/n-acetyl-l-cysteine reagent Resulting iso-indole derivative absorb at 335 nm Quantification by using calibration curve using known iso-leucine concentrations FOSS (FAN + NH 3 ) 8

9 Comparison of N 2 methods Formol solutions needs to be made fresh each time Neither method measure proline no alpha amino group and cannot be utilized by yeast Good correlation between Formol titration and NOPA (R corr = 0.97) (Shively and Henick- King, 2001) Similar results NOPA are for instance the reference method for calibration of new technology such as MIR Adjusting N levels DAP (di-ammonium phosphate) most popular Easy and cheap Approximately 5 mg/l DAP for 1 N mg/l added Adjustment needed before inoculation for cell growth Any additional addition must be made before the half way point ( < 8% alc) 9

10 Laccase activity Enzymatic analysis Activity measurement based on rate the enzyme oxidizes syringaldazine to a purple colored oxidation product Measured at 530 nm with spectrophotometer Activity expressed as U/mL Unfortunately not very sensitive SO 2 and ascorbic acid interfere with analysis Ranges from 0 in sound fruit to 140 U/mL 5-10 U/mL indicate some influence of laccase >10 U/mL apparent influence likely Laccase activity Why measure? If Botrytis in the vineyard knowing the number and potential risk Better adaptation during the winemaking process 10

11 Must/wine analysis Sulfur dioxide analysis (free and bound) Why use? Antimicrobial and antioxidant properties Why measure? Regulatory Too little no protection Too much inhibit yeast, used to produce sulfides Sulfur dioxide analysis (free and bound) How to measure Aspiration method Stream of air through acidified solution passes released SO 2 through H 2 O 2 solution H kondenseerder 2 O 2 + SO 2 H 2 SO 4 Titrated with NaOH Boiling releases bound SO 2 Ripper method (Metrohm) Titration with iodine (redox reaction), less accurate because phenols and sugars also oxidized by I 2 Winescan SO 2 (new application) lug 0.3% H 2 O 2 indikator Measure free and total SO 2 wyn 25% v/v H PO

12 Automatic analyzers FTIR (FOSS) How does it work? Phenol analyses Folin-Ciocalteu Measures all OH groups Interference from sugar, also readily reduces oxidized substances; ascorbic acid, SO 2 etc. FC reagent (yellow) oxidizes phenols and reduced product (blue-green) measured at 765 nm [Phenol] in gallic acid equivalents (GAE) mg/l 12

13 Phenol analyses Adams-Harbertson assay Measurement combines protein precipitation and traditional sulfur dioxide bleaching to determine tannin, anthocyanins and polymeric pigments Tannin measurement by AH-assay found to correlate the best to astringency Anth determination corr with other anth measurements Phenol analyses Folin-Ciocalteu Why measure? Phenols source of browning substance Responsible for color and taste (astringency) Aging potential Useful if historic knowledge of grapes and wine style aiming for Could adapt winemaking accordingly Range of values white table wine (40 1,300, av 225; red table wine 190 3,800, av 1,800) 13

14 Phenol analyses Color measurements (280, 420 and 520 nm) 280 nm similar to FC indication of total phenolics 520 nm red color [anthocyanin] mau 200 A = c 175 A = absorbance = extinction coefficient = pathlength (cm) c = concentration of sample nm Corr HPLC analysis, less expensive Phenol analysis Anthocyanin profile by RP-HPLC mau Color measurements (280, 420 and nm) 520 nm 280 nm similar to FC indication of total phenolics 520 nm red color [anthocyanin] Corr HPLC analysis, less expensive Delphnidin-3-gluc Cyanidin-3-gluc Petunidin-3-gluc Peonidin-3-gluc Malvidin-3-gluc Pet-3-gluc-acetate Peo-3-gluc-acetate Malv-3-gluc-acetate Delp-3-gluc-p-coum Pet-3-gluc-p-coum Peo-3-gluc-p-coum Malv-3-gluc-p-coum Polymeric pigments min 14

15 Why measure color? Determine opt time to harvest Red color major quality indicator for red wine Color corr with wine quality Aging potential Historical knowledge/values of vineyard or wine style to compare adapt winemaking practices 280/520 ratio quality indicator Depends on terroir Personally found it between 1 to 3 Juice analysis Many many more chemical analyses Phenol compounds of interest RP-HPLC Catechin, epicatechin, resveratrol, quercetrin Anti-oxidant potential Glutathione Absorbance Gallic acid Caftaric acid Catechin Quercetin-3-glucoside Polymeric phenols Time (min) 15

16 Conclusions A lot of supportive data available Essential for good winemaking practices Numbers are more a guidance then an exact science In more difficult years Larger need for supportive data to be able to adapt Compositional data useful in building knowledge base regarding specific vineyards and/or wines Valuable when aiming for similar wine style Determine optimal harvest date QUESTIONS? 16