Malic acid: Preparation for malolactic fermentation

Malolactic fermentation (MLF) has been practiced by winemakers for many a year but the benefits have not always been widely acclaimed. But, as Jackson (Wine Science: Principles and Applications, 3rd ed., Elsevier, 2008) notes, the controversy seems to be over and it is now generally accepted that the process can impact wines as follows (Lerm et al., Malolactic Fermentation: The ABCs of MLF, S. Afr. J. Enol. Vitic., 31 (2), 2010):

• Deacidification, with a resultant increase in pH
• Contribute to the microbial stability through removal of malic acid as a possible carbon substrate; and
• Modification of the wine's aroma profile.

In its simplest terms, MLF is the conversion of the "hard" malic acids into the softer lactic acid by lactic acid bacteria (LAB). But what is the origin of the malic acid so unceremoniously neutered? And what was the path that it trod to get here? I explore these questions in this post.

As shown in the figure below, malate makes its first appearance in the grape berry in Stage I of its development. Malic acid is produced in the berry by one of two processes: (i) Fixation of carbon dioxide by PEP carboxylase (an enzyme that catalyzes the addition of bicarbonate to PEP to form oxaloacetate and inorganic phosphate) and (ii) synthesis from sugars via glycolysis and the Tricarboxylic acid cycle (TCA). The oxaloacetic acid produced in the PEPC process is reduced to malate by the enzyme malate dehydrogenase (MDH)

Grape berry development (Source:www.extension.org)

It is estimated that tartaric and malic acids constitute between 70% and 90% of total berry acid content, with malic acid's contribution on the order of 23% - 40%. Malic acid concentration increases constantly in the first stage of development, increases sharply in Stage II, and then declines rapidly in Stage III. Prior to véraison, malic  acid levels are the highest of any of the organic acids in the berry, reaching levels of up to 25 g/L, with a resultant pH of 2.5. Pre- and post-véraison occurrences, however, contribute to a significant reduction in malic acid levels (Straus et al., Malic Acid in Wine, S. Afr. J. Enol. Vitic., 27 (2), 2006):

• Malic acid in the berry vacuoles are diluted by water influx in Stage II
• There is a significant decrease in L-malic acid biosynthesis post-véraison
• The slowing of glycolytic carbon flow during véraison results in increased glucose and fructose in the berry vacuole and a decrease in malic acid synthesis via pyruvic acid in the TCA cycle
• The biosynthesis of malic acid via the PEPC cycle is reduced due to véraison-induced lack of PEPC transcription 
• During véraison, chlorophyll is degraded so the berry shifts its metabolism from sucrose respiration to malic acid respiration.

As a result of the pre- and post-véraison retrenchments, malic acid concentration will decline to between 4 and 6.5 g/l; in some cases, getting down to 1 g/l.

A point of note is the role that malic acid plays in the development of flavor and color compounds in the berry. While the berry turns its attention to its reproductive phase -- and directs the attention of its sugars to plumping and sweetening the berry --  it fails to utilize those energy sources for the development of the compounds that are so important for wine quality. But, as I have mentioned previously, the berry is not interested in producing great wines; it is interested in genetic survival. Malic acid, then, is respired to meet the berry's energy needs for development of the flavor and color compounds.

Of the three reasons listed for malolactic fermentation, two would seem to be intrinsically related to malic acid: de-acidification and substrate for microbial instability. And de-acidification would only seem to be appropriate in the cooler-climate regions. In the warmer regions, where low acidity and high pH are already an issue, the downsides associated with the pursuit of malolactic fermentation has to be significantly outweighed by the aroma-enrichment benefits.

In his study of solutes in grape berries, Coombe (Distribution of Solutes within the Developing Grape Berry in Relation to its Morphology, AJEV, 38 (2), 1987) showed the evolution of malate levels during grape development by measuring its presence at four stages identified thusly:

1. Close to véraison, berries hard and free; 6.2ºBrix
2. Berries ripening; 10.2ºBrix
3. Early ripe stage; 17.4ºBrix
4. Overripe; 26.4ºBrix

Some of his key findings, re malate, were as follows:

• Malate was the most abundant solute in the flesh of unripe berries but declined during development by proportions comparable with the degree of increase that occurred in glucose and fructose concentrations
• The decline in malate was most notable between 10ºBrix and 17ºBrix
• The levels of malate in the skin and brush showed smaller changes as the berries developed (they were smaller to begin with and declined less over the stages of berry development)
• The malate decline in the skin occurred earlier in the regions closest to the pedicel
• Within the flesh, the lowest malate concentrations were found where vascular bundles occur.

Jackson noted that the latter point may result from "malate metabolism initiating around the axial vascular bundles and progressing outwards." Regardless, at maturity, the malic acid levels in the skin may be higher than the levels in the flesh.

The overall regional climate will determine the final berry malate levels. In colder climates, the rate of berry respiration is low and this results in immature grapes at harvest with high total acidity (TA) and low pH (Jackson, Straus et al.). In this situation, malic acid can be as much as 50% of the TA in the grape berry, resulting in a sour tasting wine. In warmer climates, conversely, the rate of malic acid respiration is higher with a resultant low (insufficient) TA and high pH at harvest. Wines made from these grapes can have a flat taste and may be susceptible to microbial spoilage (Jackson). Further, these wines may not age well. Malic acid content is thus a key factor in the determination of optimal harvest date.

According to Straus et al., mature grapes have between 2 and 6.5 g/l at maturity with levels above that only present in grapes harvested after cold summers in the cool-climate viticultural regions of the world. In those cases, the levels could rise to as much as 15 - 16 g/l. And the levels at harvest are, for the most part, the levels in the wine when the decision regarding malolactic fermentation is made. The type of crushing equipment used may have some impact on malic acid levels but that is minimal (Jackson).  Also, according to Jackson, during alcoholic fermentation, the yeasts may increase the wine pH by converting some of the malic acid to lactic acid but this is highly variable by yeast strain and has not been established to any reliable degree.

So, after its many contributions along the way; its sacrifices to keep the berry alive during its most vulnerable time, this is malic acid's reward. A neutering; a sex change operation by some egotistic, self-serving winemaker who wants to make his/her wine softer. Where are your cojones man? Well that is not a question that I can answer. When I next visit this topic I will look at the other player in this drama: the lactic acid bacteria.


©Wine -- Mise en abyme

Our road to Burgundy: Stateside steps

Ron and Bev Siegel are easily the most accomplished, endowed, and knowledgeable wine collectors in the Orlando area. They also happen to be exceptionally good friends with whom we spend a lot of time locally as well as at out-of-town food and wine events. So when I received an email from Ron at 12:46 pm on 9/24/13 regarding a trip to Burgundy, with Raj Par as the Shepherd, my terse reply (at 1:17 pm) was "let's do it."

Ron and Bev with Serge Hochar of Chateau Musar

The trip was being offered by an organization called IfOnly (ifOnly.com) which seeks to connect individuals with "luminaries" in the fields of food, wine, golf, etc., in order to realize experiences that "amaze and inspire." The purchasers are exposed to amazing experiences while the "luminary" benefits in that a donation is made to his or her named. The ifOnly descriptor for the Burgundy tour is presented below.

This trip was tailor made for us:

• Did I mention that Ron is a very serious Burgundy collector with multiple instances of the leading vintages of the leading producers resident in his cellars?
• Did I mention that while he was in kindergarten and the other kids were learning their ABCs he was learning his DRCs?
• We drink a lot of "passable" Burgundy. For example,

Missing Link Tasting

Mini-DRC vertical at Bern's Steakhouse

Dinner at the residence of the owner of The Wine Barn

Dinner at Victoria and Albert Chef's Table

Burgundy Tasting at Capital Grille

• Neither of us had previously visited the Burgundy region
• We wanted to do so badly but wanted to do it "the right way"
• The proposed trip -- with its promise of unparalleled access to the leading winemakers in the region and the opportunity to tap into the mind and habits of one of the leading wine experts of our time -- seemed the optimal manner in which to see Burgundy and its potential exceeded even our wildest musings. 

On September 30, Ron informed me that we had secured the booking. On October 1, Katie from ifOnly contacted Ron to let us know that she was going to be meeting with Raj on the following day to get some potential dates for the trip. She did end up speaking with Raj by phone on that same day and the best fit for him was April 30th to May 2nd. I did not even have to look at my calendar to know that I was going to be in Burgundy over those days. This was concrete; everything else was jelly.

The next step was for us to connect with Raj to get a sense of what an agenda would look like.Ron spearheaded this activity and when I checked in with him a few days later to find out what progress had been made, I found out that he had bought a whole heap of Sandhi wines (Raj is the winemaker for the Sandhi label). Hey, I thought you were going to engage him on our trip and instead you come away owning some California wine. You don't even like California wines. This guy needs an intervention. Well at least he had given Raj a listing of the producers that we would like to visit during the course of the trip.

After our year-end round of parties, we began serious planning for the trip. My idea of a plan is something you do two days before you need to be there; Ron's idea is to actually construct an itinerary, make reservations, and get it out of the way. I succumbed. We traded ideas about eating places in Paris and Beaune and settled on two touch points: Le Taillevent in Paris and bistro de l'hotel Beaune in Burgundy.

Ron wanted very much to ensure that we would visit DRC while in Burgundy so was leaving nothing to chance. He tapped every source and contact that he had in an attempt to get an entree and ran up a lot of dead-ends but kept on trying until he finally hit paydirt. We were going to visit DRC as our first appointment in Burgundy on April 30.

On April 10th, Raj emailed to say that Dujac and Rousseau were confirmed. He also indicated that May 1 and 2 were national holidays in France and it was proving difficult to get anyone to commit to meeting with us on this days. On April 19th he emailed us with the final itinerary:

April 30: DRC, Rousseau, and Roulot
May 1st: Carillon
May 2nd: Dujac, Mugneret-GIbourg, Faiveley

In that email he also proposed that we meet for dinner in Beaune on the evening of April 29th. We already had booked dinner for four at bistro de l'Hotel so we added two seats to our reservation in order to make that happen.

One of the issues that we had to work out was how we would travel from Paris to Beaune. I love driving in France so I had gone ahead and booked a van with Europcar. I alerted the team to this and, while Ron was open, the wives were dead set against it. They wanted to take the train. I have traveled with Ron and Bev before and I have seen their luggage. Good luck wrestling with that on a train. The women suggested that we could take smaller suitcases for the Burgundy portion of the trip and leave the larger suitcases with the Paris hotel as we would be returning to spend Saturday in Paris. We punted and said we would make the decision later. In the meantime I held on to my reservation with Euopcar. And my reservation at the little lunch hideaway between Paris and Beaune.

On the morning of April 26th, I headed to Paris by way of Newark while Ron, launching a little later in the day, headed for the same destination via Atlanta.

Burgundy we are on our way.


©Wine -- Mise en abyme

Potential contributors to "stuck" alcoholic fermentations

In the recent past, I wrote a post on stuck fermentations and identified a number of contributory factors. In this post I expand on a number of those factors. 

Let us begin with some definitions. According to Bisson (Stuck and Sluggish Fermentations, AJEV 50(1) 1999), “Incomplete or stuck enological fermentations are defined as those leaving a higher than desired residual sugar content in the wine at the end of the alcoholic fermentation.” Arrested fermentations are generally the result of conditions in the grape juice that lead to cell death and a concomitant reduction in viable biomass and sugar conversion. Some of the contributors to the aberrant conditions are listed below:

• High sugar concentration – According to Jackson (Wine Science: Principles and Applications, 3rd edition, Elsevier, New York, 2008), at sugar concentrations in excess of 25 – 30%, the potential for stuck fermentations increases significantly. High sugar content can cause cells to lose water through osmosis and contract, resulting in slow or incomplete fermentation. High sugar content also increases the production of acetic acid and its esters.

• Nutrient limitation – According to Bisson, lack of macronutrients such as nitrogen and phosphate can lead to stuck fermentations; as will an imbalance of  pH and potassium ions. Adequate levels of nitrogen are required in both the growth and stationary phases. In the stationary phase, it is required as: (i) an energy source, (ii) amino acid for synthesis of actively degraded proteins, and (iii) compounds needed to minimize the inhibitory effects of ethanol. Nitrogen is especially important in the re-synthesis of sugar transporters and the supply must be available early enough to be stored in the cell vacuole rather than have its translocation inhibited by later high ethanol concentrations. According to Allison Crowe (Avoiding Stuck Ferments, Wine Business Monthly, August 2007), macronutrients, micronutrients, and long chain fatty acids and sterols are all “important for healthy yeast growth, reproduction and survival as heat and alcohol increase in fermentation.” 

• Ethanol toxicity -- According to Jackson, S. cerevisiae is highly tolerant of alcohol toxicity but increasing alcohol buildup eventually inhibits fermentation by suppression of sugar uptake.

• Low pH -- Cerevisiae is tolerant to low pH. According to Bisson, it can grow in the range of 2.8 to 4.2 but growth and fermentation are significantly affected at levels below 2.8.

• Temperature extremes – According to Jackson, the growth rate of yeast cells is strongly influenced by temperature, with experiments showing significant reductions in cell division for every 10 degrees C increase in temperature. Excessively high temperature affects membrane fluidity and, therefore, transporter performance, and may induce stuck fermentations. Red wines are typically fermented between 24 and 27 degrees C. Dr. Murli Dharmadhikari (Lactic Acid Bacteria and Wine Spoilage, extension.iastate.edu) admonishes us to not allow fermentation temperatures to rise above 30℃. According to A.P. Haynk (The control of temperature in wine fermentation, July 1897), “For normal must with a normal yeast, the death point is 98-100℉ (36.6℃+). Before this point, however, the yeast stops working and bacteria begins to grow.

• Zymostatic and zymocidal toxins – Killer factors, molds, organic and medium-chain fatty acids, and fungicides and pesticides used in the vineyard are all cited by Bisson as potentially toxic to the yeast during fermentation. 

• Microbiological activity – This is the biggest source of volatile acidity. Could be triggered by wild yeasts, malolactic bacteria and acetic bacteria (Wynboer.co.za). Fermentations which include high populations of non-Saccharomyces yeast and bacteria are at risk of arrest because of the competition for nutrients plus the production of inhibitory factors. According to Bisson, some Saccharomyces strains are especially subject to inhibition by malolactic bacteria. An arrested fermentation of this type requires that the compromised biomass be removed in order to attempt re-starting the fermentation.

• Acetic acid -- There seems to be some confusion in the literature as to the role of acetic acid in stuck fermentations. According to Eglinton and Henschke, “Acetic acid toxicity has been suggested as a cause of stuck fermentation because it can inhibit the growth and fermentation activity of S. cerevisiae.” Rasmussen et al. (Acetic Acid as a Causative Agent in Producing Stuck Fermentations, AJEV 46(2), 1995), showed that removal of acetic acid from stuck lots with a Vinovation process resulted in prompt re-initiation of fermentation. Adding inoculants to the lots further “advanced “ the re-fermentation process. On the other side of the coin, Dr. Dharmadhikari notes “serious spoilage” occurring in musts with stuck fermentations because lactic acid bacteria can attack sugar (according to Dr. Daharmadhikari, lactic acid bacteria metabolizes sugars such as glucose and sucrose and produces lactic and acetic acid as by-products) and increase the VA levels in the wine. Bisson and Butzke see elevated levels of acetic acid leading to a stuck fermentation but they see that as a result of a problem fermentation rather than as the cause. In other words, the problem fermentation has some underlying cause which itself leads to elevated levels of acetic acid production and a stuck fermentation. In that case, getting rid of the acetic acid will still not have solved the underlying problem.

According to Bisson and Butzke, “The consensus strategy for re-initiation of stuck fermentations involves first removal of the settled yeast biomass followed by re-inoculation with a starter ‘adapted’ to the arrested environment.” Removal of the settled yeast biomass is accomplished by racking the wine off the lees and this will, in some cases, lead to a spontaneous restart of the fermentation. The conditions which are alleviated by racking off the lees are (Bisson and Butzke):

• Sterol or fatty acid limitation
• Exposure to temperature extremes. 

If there are no other contributing limitations (and, in the case of extreme temperature, once the temperature is restored to an acceptable range), racking will, in some cases, lead to a spontaneous re-initiation of stuck ferments. If, for example, one of the above limitations is combined with nitrogen or micronutrient limitations, racking alone will not suffice (Bisson and Butzke). 

©Wine -- Mise en abyme

The Côte de Beaune (Burgundy, France) and its Grand Cru clusters

The Côte de Beaune is the southern portion of the Côte d'Or and runs for 20 km north to south from Ladoix-Serrigny to the hillside of Maranges.

Côte de Beaune

It is wetter and warmer in the Côte de Beaune than it is in the Côte de Nuit. Henri Jayer says that this is a result of a greater marine influence on Côte de Beaune. The relative warmth aids ripening and allows picking of the Côte de Beaune vineyards two days prior to the initiation of Côte de Nuit harvest. That being said, the major climatic influences associated with the greater Côte d'Or are relevant to the Côte de Beaune.

According to legendary Burgundy winemaker Henri Jayer (A Tribute to the Great Wines of Burgundy), the soils from Ladoix to Meursault are from the Late Jurassic, with Oxfordian and Callovian series' predominant (This would actually qualify as Middle-Late as the Callovian actually falls in the Mid-Jurassic period.). The mostly red marl, consisting, according to Jayer, of half-chalk and half-clay, is Pinot-Noir-friendly, producing supple and fruity red wines which are less structured and tannic than Côte de Nuit reds. These wines mature earlier than do the Nuit reds but, in the best years, will age well.

From Meursault to the middle of Chassagne-Montrachet, the middle Jurassic becomes evident . The sediments here were not completely transformed to limestone and were deposited in the area as white marl. Chardonnay thrives on this soil. Hence the Grand Crus of Chassagne- and Puligny-Montrachet. From the middle of Chassagne, the soil again becomes Mid-Late Jurassic, making way for light, supple Pinot Noir wines.

The Hill of Corton heralds the beginning of the Côte de Beaune wine region and, one would think, a sea of white wine.

The top of the hill is covered by dense woodland which gives way to cap rock of Rauracian limestone. Vineyard-capable limestone soils begin at about 345 meters and slope gently to the valley floor through "terroirs of distinction." The upper slopes are rich in marl and Chardonnay flourishes on the western side of the hill while Pinot Noir grows on the western side beginning at 330 meters elevation where Late Jurassic soils kick in. Two great Grand Cru vineyards share the hill: Corton (mostly red) and Corton-Charlemagne (white).

Source: burgundyonline.com

The Corton Grand Cru appellation is associated with the famed communes of Aloxe-Corton, Ladoix-Serrigny, and Pernand-Vergelesses. The vineyard is 97.53 ha in size (4.53 ha of which is planted to Chardonnay) and sits at elevations ranging between 250 and 330 meters. The Chardonnay vines are planted in the climats of Vergennes and Languettes.

While 4.5% of the Corton Grand Cru vineyard is devoted to Chardonnay vines, 6.19% of the Grand Cru production is white wine. There are 26 Lieux-dits in the appellation and the red wines are authorized to name the Lieux-dit on the bottle following the appellation name. White wines are not so allowed.

The Côte de Beaune's second Grand Cru cluster can be found around the towns of Puligny-Montrachet and Chassagne-Montrachet, both AOCs since 1937. Puligny-Montrachet soils are either brown limestones or limestones alternating with marls and limey clays; in either case, soil depth is varying. South of Chassagne-Montrachet, the soils have a higher concentration of limestone marl and red gravel, a boon for Pinot Noir. North of the village, the harder marls are substituted by softer, finer limestone and a preponderance of Chardonnay vines. The Grand Crus -- all white wines -- in this cluster are as follows:

• Le Montrachet -- shared between the two communes
• Bâtard-Montrachet -- shared between the two communes 
• Chevalier-Montrachet -- Puligny-Montrachet
• Bienvènues-Bâtard-Montrachet -- Puligny-Montrachet
• Criots-Bâtard-Montrachet -- Chassagne-Montrachet.

In addition to the Grand Crus, the two communes support Village and Premier Cru appellations. Puligny-Montrachet hosts 17 Premier Cru vineyards while Chassagne-Montrachet hosts 55. Noted Premier Cru vineyards in Puligny-Montrachet include: Les Demoiselles, Le Cailleret, Les Pucelles, Les Combettes, and Les Folaitières. Notable PC vineyards in Chassagne-Montrachet are : Caillerets, Ruchottes, Chaumées, and La Boudriotte.

The distribution of vineyard size and production by appellation is shown in the table below.

		Village			Village and Premier Cru			Grand Cru
		Production (hl)			Production (hl)			Production (hl)
Appellation	Size (ha)	Red	White	Size (ha)	Red	White	Size (ha)	Red	White
Aloxe-Corton				118.87	4361	88
Auxey-Duresses				132.87	3319	1787
Bâtard-Montrachet							11.73		486
Beaune				416.23	12,146	2195
Bienvènues-Bâtard-Montrachet							3.58		165
Blagny				4.31		142
Chassagne-Montrachet				307.52	3906	9346
Chevalier-Montrachet							7.47		287
Chorey-lès-Beaune	126.28	4712	425
Corton							97.53	2789	151
Corton-Charlemagne							52.08		1929
Côte-de Beaune	31.76	680	269
Côte-de Beaune Village	4.66	176
Criots-Bâtard-Montrachet							1.57		67
Ladoix				98.13	2478	952
Maranges				160.84	5390	357
Meursault				399.87	458	16,563
Montrachet							8		271
Pernand-Vergelesses				138.45	2644	2373
Pommard				325.65	12,014
Puligny-Montrachet				205.72	26	10,066
Saint-Aubin				154.01	1493	5054
Saint-Romain	92.26	1409	2259
Santenay				321.87	8742	2101
Savigny-les-Beaune				354.73	11,413	1620
Volnay				220.39	7587
Totals	3399.2	6977	2953	3359.46	75977	52644	181.96	2789	3356

To summarize then, in a total vineyard area of 6940.62 ha, Côte de Beaune vignerons produce 85,743 hectoliters of red wine and 58,593 hectoliters of white wine, with a counter-intuitive, almost-60% of the production being red.

©Wine -- Mise en abyme