- What can I do to enhance the occurrence of malolactic fermentation?
- What are the applications Lysozyme?
- How do I know if my yeast is still fresh?
- I hear lots of negative comments about propagation (“mother tanking”) – are they true?
- Can you ferment white wines (Sauvignon blanc, Chardonnay) at 10 ºC?
- What is the best way to add enzymes?
- Does SO2 affect the activity of enzymes?
- What is the affect of bentonite on enzymes?
- What is the recommended dosage, temperature and contact time for enzymes?
- What is the shelf life of enzymes?
- Why are standard pectinases not recommended for red wines?
- What is the best time to add enzymes for the maceration of red grapes?
- How do enzyme activities or units used by different suppliers compare?
- What does GRAS stand for?
- How can one conduct partial MLF or stop spontaneous MLF?
- What is the organoleptic impact of MLF on wine?
- What are the ideal conditions for MLF in wine?
- What happens when MLF occurs in the presence of residual sugar?
- When is the best time to inoculate for MLF?
1. What can I do to enhance the occurrence of malolactic fermentation?
A number of factors contribute towards successful malolactic fermentations, and it should be remembered that these factors act synergistically. The contributing factors are pH, temperature, alcohol, SO2 and nutrient availability. The pH should be greater than 3,1. The temperature should ideally be between 20°C and 23°C and preferably no less than 18°C. The free SO2 should be no greater than 10 ppm, (recommended total SO2 for white wine 40 ppm and for red wine 70 ppm). Above 14%, alcohol becomes a significant inhibitor of malolactic fermentation. If using a starter culture, the best time of addition is either at the end of alcoholic fermentation or 24 hours after the onset of alcoholic fermentation. Use only bacterial strains proven suitable for co-inoculation if you are considering the latter.
There can often be a nutrient deficiency, the most important of which is a nitrogen source. Lactic acid bacteria utilise amino acids as a nitrogen source and not ammonia. Adding DAP will therefore not be effective as a nitrogen source. The addition of specialised bacterial nutrients containing amino acids, vitamins and minerals are advised. The use of pure yeast cell walls can also enhance bacterial growth since it removes toxic medium chain fatty acids produced by yeast during fermentation. These medium chain fatty acids can be inhibitory to lactic acid bacteria.
2. What are the applications of Lysozyme?
Lysozyme is an enzyme (protein) derived from egg white and has been safely used in the food industry for a number of years. It acts to inhibit gram positive bacteria and has been demonstrated to inhibit lactic acid bacteria, including malolactic bacteria, in wine. It can be used to either delay or inhibit malolactic fermentation. This may be required with some bottle fermented sparkling wines, during lagging or stuck fermentations or for micro-oxygenation. It can also be used to inhibit bacterial spoilage in wine where reduced sulphur dioxide is used,or wines with a high pH, under which conditions sulphur dioxide is less effective.
3. How do I know if my yeast is still fresh?
The vacuum brick should still be hard (it will last for 3 months if it has just gone soft or after opening). Check the date stamp, it should be within the expiry date or within 2 years of the production date. Check also that the product has not been heated as this could have adverse effects on the quality.
4. I hear lots of negative comments about propagation (“mother tanking”) – are they true?
It is definitely better to use direct inoculation as this will help to prevent lagging and stuck fermentations, as well as ensure that the overall fermentation profile is better. Propagation in the presence of alcohol and the absence of oxygen (as is the case with winery produced yeast) reduces the sterol levels in the yeast cells, which has a negative effect on alcohol tolerance. Yeast companies propagate yeast in the absence of alcohol and in the presence of vast quantities purified compressed air containing oxygen. This way of production is very conducive to the production of sterols and long chain fatty acids that play an integral part in ensuring yeast membrane integrity and therefore alcohol tolerance.
5. Can you ferment white wines (Sauvignon blanc, Chardonnay) at 10 ºC?
Yes it is possible although very few wine yeasts can ferment at such a low temperature. The only advantage of fermenting very cold is increased aromatic ester production. Fermenting Chardonnay very cold will increase banana and pineapple aromas if a wine yeast capable of producing those esters are used.. In the case of Sauvignon Blanc we do not recommend such low temperatures. The typical varietal aroma of S. blanc is expressed at slightly higher fermentation temperatures. In general the colder the fermentation, the less mouth feel in a wine.
6. What is the best way to add enzymes?
Granulated enzymes must be suspended in non-sulphated juice before addition. Never mix it with pure water. For a homogenous distribution the enzyme solution can be sprayed or dripped over the grapes during crushing. In the case of certain varieties settling enzymes can also be added directly into the settling tank if contact with grapes skins must be kept to a minimum.
7. Does SO2 affect the activity of enzymes?
Yes it does but only in very high dosages. These dosages are usually way above the legal limit of SO2 concentrations permitted in wines and is therefore not a factor. However, care must be taken when making enzyme and SO2 additions at crushing. It is recommended that the SO2 addition is made before the enzyme addition to the grapes and that the SO2 is allowed to disperse, i.e. become diluted, before the addition of the enzyme.
8. What is the affect of bentonite on enzymes?
Bentonite is negatively charged and absorbs positively charged molecules such as proteins rather non-specifically. Enzymes are proteins and are absorbed by and therefore inactivated by bentonite. It is generally not recommended to settle with bentonite since it could have an effect on the fermentation performance of the yeast. However in the case of Botrytis infection, settling with bentonite is inevitable since one must remove the laccase enzyme. If you need to add enzyme to a bentonite treated must or wine make sure the must/wine is completely racked off the bentonite lees before making any enzyme additions.
9. What is the recommended dosage, temperature and contact time for enzymes?
It depends on the specific enzyme application, i.e. settling, white skin contact, red skin contact etc. The three parameters influence each other. For instance in the case of white skin contact, the higher the temperature – the shorter the contact time and the lower the dosage. Different enzymes have different recommended dosages and instructions must be followed very carefully for optimum results. More is not necessarily better and one can over macerate. In the case of white musts over maceration is characterised by very clear juice at the top of the tank, very compact lees at the bottom and a meter or two (depending on the tank size) of “fluff” that is impossible to settle. This fluff is little pieces of grape skin that is broken into small pieces. It is only necessary to break skin cells open to obtain more juice and flavours, not to break it into small little pieces.
10. What is the shelf life of enzymes?
Granulated enzymes are very stable if stored under the recommended conditions. Their shelf life is usually indicated as 3 years but it is actually longer if they remain un-opened. Liquid enzymes are less stable than granulated enzymes but if stored under the correct conditions the activity loss is minor and can usually be corrected with an increase in dosage.
11. Why are standard pectinases not recommended for red wines?
Standard pectinases, not specific for red skin contact, contain an activity known as anthocyanase. This is the generic name and the actual enzymes are different types of glycosidases. Glycosidases remove sugar molecules from more complex molecules from which anthocyanin is one. Anthocyanins are stabilised by the sugar components bound to them and when removed, the anthocyanin becomes unstable and colourless. Standard pectinase preparations contain these activities because A. niger species usually produce a “cocktail” of enzymes. In the case of red skin contact enzymes, the anthocyanase activity must be below the levels that can be harmful to red wine colour. Some enzyme companies make sure that this is the case, some don’t. Make sure that that you use a red skin contact enzyme that specifies that this activity is negligible. Glycosidases are very positive for white wine aroma so their presence in white enzymes is a positive.
12. What is the best time to add enzymes for the maceration of red grapes?
Enzymes should be added as early as possible, preferably at the time of crushing since this is the beginning of the colour extraction phase of red wine maceration. Most colour extraction takes place at the beginning of fermentation whereas tannin extraction takes place towards the end of fermentation and during post fermentation maceration.
13. How do enzyme activities or units used by different suppliers compare?
They don’t compare at all. Companies use different substrates to measure activities as well as express the activities in different units. The only way to compare products is to do trials.
14. What does GRAS stand for?
GRAS stands for Generally Regarded As Safe. This statement applies to microorganisms used in the food industry. Wine enzymes may only be produced from GRAS organisms.
15. How can one conduct partial MLF or stop spontaneous MLF?
It is quite difficult to stop spontaneous MLF once it has started. If partial MLF is desired on a wine it is best to blend wine that has completed MLF with a wine that has not undergone MLF. In order to prevent MLF completely one can use several methods either separately or in combination. These factors are low temperatures (below 18°C), sulphur dioxide (inhibitory to LAB) and lysozyme (kills LAB).
16. What is the organoleptic impact of MLF on wine?
Malic acid is converted to lactic acid that is less acidic than the former. This loss in acidity and accompanied increased pH has a profound effect on taste. During MLF new aromatic compounds are formed that can change the aroma profile of a wine and increase mouth-feel. MLF is also characterised by the slight decrease in upfront fruit intensity and freshness of a wine. Generally a wine that has been through MLF can be well balanced with a complex aromatic profile. MLF is mostly done in red wines and is only suited to certain white grape varieties.
17. What are the ideal conditions for MLF in wine?
-Alcohol below 14%
-Temperature above 18°C
-pH above 3.2
-Total SO2 below 40 for white and 70 ppm for red
-Free SO2 below 10 ppm
-Minimum number of cells: 106 CFU / ml.
18. What happens when MLF occurs in the presence of residual sugar?
If LAB starts to grow before the end of alcoholic fermentation some strains can utilise glucose and fructose instead of malic acid. The result is different end products leading to an increase in “buttery flavour” and volatile acidity.
19. When is the best time to inoculate for MLF?
The best time for MLF is either the same time as alcoholic fermentation or right after alcoholic fermentation. Wine temperature will be elevated – and therefore very suitable for MLF – due to heat generated by the yeast during fermentation. After completion of fermentation various cellular components “leak” into the wine through the weak yeast cell membrane and cell wall. These components include amino acids and nucleotides that can serve as organic nitrogen for LAB. It has also been proved that small quantities of CO2 help LAB develop.