Showing posts from January, 2020

Why your should stay away from fermentation temperatures above 30°C

By Karien O'Kennedy Spanish researchers from Argentina and Spain evaluated the effect of cold and hot temperature shocks on fermenting yeasts. These temperature shocks are usually referred to as thermal shocks in scientific literature and the “how to use guidelines” of commercial yeast companies. The researchers also looked at the effect that DAP addition, before the thermal shocks, had on the recovery of the yeast after such a shock. What they did The researchers exposed two different yeasts to cold shocks and three different yeasts to heat shocks in small scale fermentations conducted in synthetic grape juice. The cold shocks comprised abruptly lowering fermentation temperature to either 9°C or 1.5°C for 16 hours; two, six, 10 or 14 days after the start of fermentation. A daily cold shock variable was also included where the temperature was lowered to 1.5°C every night and allowed to return to room temperature (26°C) during the day. Three yeasts were expose

Dead yeasts adsorb red wine colour

By Karien O'Kennedy It was previously found that yeasts can negatively affect wine colour in two ways: via their β-glycosidase enzymatic activity (removing the sugars from monomeric anthocyanins and thus rendering them colourless), and through direct adsorption of anthocyanins on the yeasts’ cell walls. Brazilian researchers evaluated the effect of five different commercial yeasts on red wine colour. The yeasts were previously grouped into three categories namely low, medium and high yeast pigment adsorption phenotypes. This grouping was done by the same researchers during their development of a method to test the adsorption capacity of yeasts. The current research Small scale fermentations were conducted using a 50/50 Merlot/Tannat must combination that underwent a laboratory scale thermovinification process. The researchers measured the anthocyanin adsorption overall, as well as that of individual cells. What they found The researchers found that yeasts

Fighting vineyard pathogens with UV light

By Lucinda Heyns The aim of this project was to determine if UV light can be used to reduce or eliminate the incidence of powdery and downy mildew in vineyards.   Project layout: - Two different UV light treatments (100 J/m 2 and 200 J/m 2 ) were applied weekly to Chardonnay vines using a UV light array on a tractor drawn carriage. Based on previous laboratory trials, it was expected that these treatments should stop 80% - 100% of the powdery mildew conidia from germinating.  - Treated vines received only UV light, no other fungicides.  - In another treatment, vines received only conventional fungicides.  - There was also a control where no fungicides or UV light were applied.  - The trial was done in a year where powdery mildew pressure was moderate and downy mildew pressure was severely high. Results Powdery mildew - Severity of powdery mildew in the control vines were 15%. - Both UV treatments significantly reduced the severity of powdery mildew on

Do mychorrizal fungi survive root pruning?

By Lucinda Heyns In this study, researchers wanted to determine whether trimming of roots of young vines prior to planting affects mycorrhizal fungi on the roots. Arbuscular mycorrhizal fungi are symbiotic fungi which are beneficial to plants by helping plants to capture nutrients from the soil. They are sometimes applied as biofertilizers to young vines before planting, with the intention to aid establishment of the vines once they are transplanted into the field. Often the roots of the young vines are trimmed prior to planting to avoid J-rooting and to ensure the roots fit comfortably into the planting hole. It is not known whether root trimming removes active mycelium, therefor losing all the benefits of the inoculation. By means of a greenhouse experiment, researchers tested how root trimming affects mycorrhizal fungi on vine roots. Conclusions: Mychorrizal symbiosis persisted on roots, despite root trimming. This is probably because the fungal structures lef