Hello wine fans, I have been out of the blogging business for a while as I have been gutting and remodeling a house for my daughter. Now that I am semi-retired, I am supposed to have all this time on my hands but for what it’s worth, I feel busier than I did when I ran my company. In any case I want to get back at it and one of my favorite winemakers, Rod Easthope from KIWI country did this really neat description of part of the Wine making process known as Malolactic fermentation and gave me permission to re post it as a guest blog on Poor Robert’s so here it is. For those that don’t make wine it really provides an insight into what happens in the process as well as what goes on in the winemakers head –enjoy —
There are probably winemakers who post a lot more often than me. However, I only feel compelled to post when there is something meaningful to say. For me and my winegrowing that tends to be catalysed by seasonal affects rather than more frequent incremental moments.
Well spring has sprung here. When I travel to the cellar and see bouncing lambs, daffodils and fruit tree blossoms, then I know that some barrels will have popped their bungs. Why, because some beneficial naturally occurring bacteria within the maturing wine also spring to life and start devouring malic acid which is naturally present in the grapes, and converting it to lactic acid. This process also releases Carbon dioxide which bubbles to the surface and can even pop the bungs on the barrels. It becomes a daily chore to lightly replace the bungs.
Malic Acid is produced in the leaves of grapevines during the growing season and transported to the grapes. From there it is used as fuel within the grape to power respiration. Respiration is an enzymatic process, the by-products of which are all the lovely ripe flavours in mature grapes. This process is dictated by temperature; warm climates use up malic acid for respiration faster than cool climates. However, there is always some malic acid still present in the harvested grapes to varying degrees.
To me, the year of winemaking following harvest is an extension of the ripening in the vineyard to a higher order of ripeness. Grape sugars change (“ripens”) to a more complex sugar alcohol (ethanol). And malic acid in some wines styles is “ripened” to lactic acid. When you think of malic acid, then imagine green apples (the principle acid in apples is malic acid), and when you think of lactic acid then imagine milk. Lactic acid is softer and weaker in its effect on both the chemistry of the wine and the palate of the imbiber.
The bacteria that perform this trick are also temperature sensitive. Many winemakers will artificially warm their wines in autumn and add commercially prepared bacteria to induce this process. I have always favoured letting nature take its course, and hence it is not until spring when the barrels naturally warm that the wild bacteria complete malolactic ferment (MLF).
Because red wines have tannins and hence astringency to provide balance to the alcohol and fruit flavours, any malic acid presence would magnify this and the wine would seem bitter and even green flavoured. That’s why nearly all red wine completes MLF. With white wines it becomes a stylistic choice dependent on the season, desired wine style, and wine attributes. Most full-bodied cool climate Chardonnay undergoes some degree of MLF. Whereas un-oaked whites such as Riesling, Pinot Gris and Sauvignon Blanc generally don’t have any MLF – the malic acid here is deemed to provide freshness and balance to fruit driven varietals.
The fringe benefit of MLF is there is one less fermentable element when the wine goes to bottle. This means, for dry wines (no sugar present), which have fully completed MLF (no malic acid present) that there is no risk of re-fermentation in bottle, and therefore lower preservative levels can be used and reduced filtration employed. That’s part of the reason why dry red wines generally have less Sulphur added than white wines.
I hope this very over-simplified overview of MLF provides some insight. For me – time to dodge the marauding lambs, avoid trampling the daffodils and gently replace those bungs.
Contributed and republished with permission graciously given by Rod Easthope, Winemaker.