Temperature maceration

Red wines have average nitrogen concentrations almost twice as high as those of white wines. This is dne to winemaking techniqnes, inclnding high-temperature maceration, which causes nitrogenated substances to dissolve more readily from the skins and seeds, as well as autolysis of dead yeast cells. 

Post-fermentation vatting is required by the best premium quality red wines to prolong skin contact after the end of fermentation, sometimes combined with an increase in temperature (final, high-temperature maceration, 12.5.5). 

However, the dissolvent effect of SO2 is manifest in rose winemaking, since the phenolic compound concentration is low in this case. In fact, SO2 can be detrimental to white winemaking. This dissolvent effect may also affect red grapes if they are insufficiently ripe, and pigment extractability is poor. In that case, snlfiting facilitates anthocyanin extraction in the early stages, especially during cool-temperature maceration (Section 12.5.2). 

Single-base propellants are mixed in a similar fashion by adding the ingredients to the nitrocellulose in the mixer together with the required amounts of ether and alcohol. The mixing time is about one-half hour, and the temperature is kept below 25°C. The pardy colloidal mixture looks like moist cmde sugar. A maceration step may be included to increase homogeneity. 

In the older method, still used in some CIS and East European tar refineries, the naphthalene oil is cooled to ambient temperatures in pans, the residual oil is separated from the crystals, and the cmde drained naphthalene is macerated and centrifuged. The so-called whizzed naphthalene crystallizes at ca 72—76°C. This product is subjected to 35 MPa (350 atm) at 60—70°C for several minutes in a mechanical press. The lower melting layers of the crystals ate expressed as Hquid, giving a product crystallizing at 78—78.5°C (95.5—96.5% pure). This grade, satisfactory for oxidation to phthaHc anhydride, is referred to as hot-pressed or phthaHc-grade naphthalene. 

Fermentation. The term fermentation arose from the misconception that black tea production is a microbial process (73). The conversion of green leaf to black tea was recognized as an oxidative process initiated by tea—enzyme catalysis circa 1901 (74). The process, which starts at the onset of maceration, is allowed to continue under ambient conditions. Leaf temperature is maintained at less than 25—30°C as lower (15—25°C) temperatures improve flavor (75). Temperature control and air diffusion are faciUtated by distributing macerated leaf in layers 5—8 cm deep on the factory floor, but more often on racked trays in a fermentation room maintained at a high rh and at the lowest feasible temperature. Depending on the nature of the leaf, the maceration techniques, the ambient temperature, and the style of tea desired, the fermentation time can vary from 45 min to 3 h. More highly controlled systems depend on the timed conveyance of macerated leaf on mesh belts for forced-air circulation. If the system is enclosed, humidity and temperature control are improved (76). 

The molten part of a vitrinite is similar to the gross maceral, and a part of the maceral is converted to a form that can be melted after heating to 300—400°C. The molten material is unstable and forms a soHd product (coke) above 350°C at rates that increase with temperature. The decomposition of the Hquid phase is rapid for lower rank noncoking coals, and less rapid for prime coking coals. The material that melts resembles coal rather than tar and, depending on rank, only a slight or moderate amount is volatile. 

Maceration of crnshed or gronnd material in methanol containing small amounts of HCl (<1%) is commonly used at refrigerated temperatures for times ranging from a few hours to overnight. The extracted material is usually too dilute for further analyses and the extraction procednre is usually followed by evaporation of the methanol using vacnnm and mild temperatures (30 to 40°C). Alternatively, the plant materials and solvents can be mixed well with a laboratory blender for a few minutes or a chemical-resistant stir bar for a longer time. Concentration of anthocyanin extracts can be done by rotary evaporation under vacuum conditions for volatile solvents or lyophilization for water. 

It is desirable to prevent leaf temperature from rising above 35°C during the maceration process to preserve quality. 

The oxidative process actually starts with the onset of maceration of withered leaf. At the end of the rolling process leaf is allowed to oxidize in 5 to 8 cm beds on trays in another fermentation room. It is desirable to keep temperatures below 30°C. Oxidation at 15 to 20°C is said to improve flavor.79 High humidity prevents surface drying and consequent retardation of oxidation. 

The significant liquefaction yields that are presumed to have been derived from some macrinite-rich samples may attest to a contribution to conversion from this maceral. However, results from durains, and splint and cannel coals, which may contain large amounts of macrinite, generally have been variable (50). The conversion which we achieved with a coal containing 21% macrinite indicated that there was a contribution to the liquid products of batch hydrogenation from this maceral. Further, the residues examined from runs made with this coal at a series of temperatures contained no distinguishable macrinite product once a temperature of 425°C had been reached (66). 

Because of the advantageous dietary effects of flavonoids they have been vigorously investigated in food and food products. The objectives of these measurements were the separation and quantitation of well-known flavonoids in foods and the identification of new flavonoids. An HPLC-ESI MS method has been developed for the isolation and identification of new quercetin derivatives in the leaves of Eruca sativa (Mill). Fresh leaves (500g) were homogenized with 1 200 ml of methanol-water (7 3, v/v), the suspension was macerated for 24h at ambient temperature, then it was filtered, concentrated to 50 ml and diluted with water to 500 ml. The extract was applied to an Amberlite XAD-2 column (75 X 8cm i.d.) and was washed subsequently with 11 of water and 11 of diethyl ether. The glucoside fraction was eluted with 1.51 of methanol and the eluate was concentrated in vacuum and liophilized. 

Changes In nuclear magnetic resonance measurements of an extensive suite of Australian coals on heating and exposure to pyridine are used to elucidate the molecular conformation of coal macerals Two types of fusible material are Identified In these coals One Is associated with llptlnltes of all ranks and Is typified by fusion commencing at temperatures below 475 K. The other Is associated with vltrlnltes and some Inertlnltes of bituminous coals only and Is characterized by a sharp onset of fusion at temperatures above 625 K. The temperature of onset of fusion Increases with rank for both types The effect of pyridine on the molecular stability of bituminous coals at ambient conditions Is strongly dependent on maceral composition at 86% C and on rank at higher carbon contents ... 

Thermal destabilization of the molecular lattice of aromatlc-rlch macerals In bituminous coals at temperatures above 600 K Is associated with their characteristic thermoplasticity (10). The relationship between the extent of this fusion and the molecular properties of the vltrlnlte and Inertlnlte macerals, however. Is not well understood. 

The high-volatile Liddell bituminous coal (Figure 2 (E)) shows little indication of thermally-activated molecular mobility below 500 K. There is some fusion between 500 and 600 K followed by a major fusion transition above 600 K which appears very similar to the high temperature transition of the Amberley coal. This Liddell coal, however, has only 6% liptinite, has a crucible swelling number of 6.5 and exhibits considerable Gieseler fluidity. We therefore attribute this high temperature fusion event to the aromatic-rich macerals of the coal and associate it with the thermoplastic phenomenon. This implies that a stage has been reached in the coalification processes at which aromatic-rich material becomes fusible. 

The low-volatile bituminous Bulli coal which contains no liptinite and has significant thermoplastic properties has a M2J pyrogram (Figure 2 (F)) showing only one fusion transition which is lesser in extent and shifted to higher temperatures than that of the Liddell coal. This transition is, of course, attributed to aromatic-rich macerals. 

By applying this analysis at discrete 10 K temperature intervals to the NMR thermal analysis data for the 102 coals (subdivided into brown coals (<75% C), lower rank (80-85% C) and higher rank (85-90% C) bituminous coals), regression coefficients could be obtained as functions of temperature and hence the average 2T of the three maceral groups were generated (Figures 3-... 

Fusion of the llptlnlte macerals In bituminous coals commences at lower temperatures and reaches a much greater extent than that of the aromatic macerals (Figures 4 and 5). The greater thermal stability Indicated by the much higher fusion temperatures of the bituminous llptlnltes compared to brown coal llptlnltes can be explained In terms of these materials having a more highly crossllnked macromolecular structure than the llptlnltes In the brown coals. This Increase with coallflcatlon could be the consequence of In situ crosslinking of material or the selective loss of llptlnlte fractions that are less crossllnked and therefore less Inherently stable ... 

Maceration Steep herb in room-temperature water... 

White musts and wines made without maceration contain very low amounts of flavonoids. However, when making white wine from white grapes, skin contact at low temperature is sometimes performed before pressing and fermentation to increase extraction of volatile compounds and aroma precursors. After 4h of skin contact, the concentration of flavanol monomers and dimers in must was increased threefold. Delays between harvest and pressing, especially if sulfur dioxide is added to prevent oxidation, as well as thorough pressing, similarly result in increased concentrations of flavonoids in white musts and wines. " " ... 

---