PREPARATION OF OIL RICH HOP EXTRACTS AND THEIR ADDITION TO BEER ON THE PILOT-SCALE USING LIQUID CARBON DIOXIDE*

The introduction of carbon dioxide hop extracts dissolved in liquid carbon dioxide to green beer during transfer from fermentation vessel to cold conditioning tank results in a sound dry hop flavour in the finished product. A system has been developed for injecting a solution of extract into a beer main. Extracts which are rich in hop oils are particularly suitable for imparting hop character to beer and a liquid-liquid countercurrent procedure is described for producing extract fractions containing enhanced levels of essential oil.     

USE OF EXTRACTS PREPARED WITH LIQUID CARBON DIOXIDE AS A SUBSTITUTE FOR DRY HOPS

Liquid carbon dioxide hop extracts were prepared for use as a substitute for dry hops. Many of these extracts were oil rich fractions containing up to 14% (w/w) hop oil. Extracts of Styrian Golding, Wye Target and Wye Northdown hops were used to treat ales prior to completion of beer processing and subsequent packaging. Emulsion/suspension systems were developed as carriers to facilitate addition of these extracts to beers before the chilling process. A loss of hop character from beer was found to occur during fining and filtration. Beers, treated with the extracts, exhibited natural though varietally distinct dry hop character. Production scale trials using these extracts have been successfully carried out to dry hop a brewery conditioned draught bitter and to match a traditionally dry hopped premium pale ale. The quantities of extract used indicated that economies in hop usage can be achieved when substituting liquid carbon dioxide hop extracts for dry hops.     

SOLUBILITY OF HOP α- AND β-ACIDS IN LIQUID CARBON DIOXIDE*: ADDENDUM: SOLUBILITY OF PESTICIDES IN LIQUID CARBON DIOXIDE

A procedure is described for determining the solubility of hop α- and β-acids in liquid carbon dioxide. Results have shown that the optimum temperature range for the extraction of hops with liquid carbon dioxide is +5 to +10°C. A number of pesticides used by hop growers are appreciably soluble in liquid carbon dioxide.     

PRODUCTION-SCALE APPARATUS FOR THE INJECTION OF HOP EXTRACTS INTO BEER USING LIQUID CARBON DIOXIDE

Extracts of hops made with liquid carbon dioxide can be substituted for dry hops to introduce the flavour of hop oils into beer. Apparatus has been devised so that such extracts can be redissolved in liquid carbon dioxide and then metered into beer. Successful trials have been carried out on the commercial scale.     

THE STABILITY OF HOP OILS IN LIQUID CARBON DIOXIDE EXTRACTS OF HOPS

Portions of extracts obtained by treating three varieties of hops with liquid carbon dioxide were stored in the cold and at ambient temperature for 18 months. During this period the composition of nop oils remained stable, except for the formation of two terpene methyl sulphides in extracts from all three varieties. Ales were ‘dry-hopped’ using portions of the stored extracts and, despite formation of the two sulphur compounds, the resulting hop character was satisfactory in all cases.     

DIFFERENCES IN UTILISATION OF THE ESSENTIAL OIL OF HOPS DURING THE PRODUCTION OF DRY-HOPPED AND LATE-HOPPED BEERS

Late-hopped and dry-hopped beers were prepared and their lipophilic constituents extracted using Amberlite XAD-2 resin. Examination of the volatile constituents by GC-MS confirmed that most of the hop oil added towards the end of wort boiling is lost by evaporation. Part of the material which survives boiling is chemically transformed by yeast during fermentation. Dry-hopped beer contained compounds more representative of the original hop oil than did the corresponding late-hopped beer. A liquid carbon dioxide extract of hops, rich in essential oil, has been fractionated by column chromatography on alumina-silica giving preparations which simulate either late-hop or dry-hop character.     

LIQUID CO2 AND ETHANOL EXTRACTION OF HOPS PART I: EFFECT OF HOP DETERIORATION ON EXTRACTION EFFICIENCY AND EXTRACT QUALITY

Deteriorated hops were extracted with liquid carbon dioxide (LCO₂) and with ethanol. The degree of hop deterioration influences both the extraction efficiency and the composition of the resulting extracts.     

PREPARATION OF HOP EXTRACTS WITHOUT USING ORGANIC SOLVENTS

Extraction of hops with liquid carbon dioxide at ambient temperature provides an attractive means of producing hop extracts which are rich in α-acids and free from hard resins, polyphenols, pigments and residual organic solvents. The resulting yellow extracts give beer with a clean bitter flavour when they are added during wort boiling. Manufacturing costs using the process are likely to be substantially less than in a conventional hop extraction plant.     

The Oxygenated Sesquiterpenoid Fraction of Hops in Relation to the Spicy Hop Character of Beer

Hop‐derived sesquiterpenoid‐type oxidation products have been associated with a spicy or herbal hoppy beer character. However, the flavour threshold values of hitherto identified oxygenated sesquiterpenes are generally much higher than their estimated levels in beer. By applying two‐step supercritical fluid extraction of hop pellets using carbon dioxide, followed by chromatographic purification of the enriched sesquiterpenoid fraction, highly specific varietal hop oil essences containing all main oxygenated sesquiterpenes were obtained. Post‐fermentation addition (at ppb levels) of these purified sesquiterpenoid essences from various European aroma hops led to distinctive spicy or herbal flavour notes, reminiscent of typical ‘noble’ hop aroma. It is concluded that a spicy hop flavour impression in beer depends significantly on minor constituents of the natural sesquiterpenoid hop oil fraction.     

PILOT PLANT EXTRACTION OF HOPS WITH LIQUID CARBON DIOXIDE AND THE USE OF THESE EXTRACTS IN PILOT AND PRODUCTION SCALE BREWINGa

Several varieties of hop have been satisfactorily extracted using liquid carbon dioxide in a plant operating on the 1 kg scale. The extracts have been used in small scale (0·6 and 16 hl) and production scale (700–800 hl) brewing trials where both ales and lagers were produced. All beers were of sound quality and could not be distinguished organoleptically from controls brewed with either hops or commercial hop extracts.     

AUTOMATED REPORTING ON THE QUALITY OF HOPS AND HOP PRODUCTS

The quality of a hop variety or a hop product can readily be assessed by a fully automated sequence of selective extraction, fractionation and quantitative analysis. To illustrate the elegance of the method, nine hop varieties and three hop extracts were compared with respect to the content of important marker compounds in the hop oils and of the hop acids. Supercritical fluid extraction at different densities of carbon dioxide was applied to extract selectively, the hop oils and the hop acids, respectively. The hop oils were further fractionated into an apolar and a polar fraction by solid phase extraction and consecutive elution with n-hexane and ethyl acetate. Separation and identification were achieved by capillary gas chromatography coupled to mass spectrometry. Myrcene, β;-caryophyllene, α;-humulene and β;-farnesene in the apolar fraction, linalool, undecan-2-one, tridecan-2-one and humuladienone in the polar fraction were selected for quantitative evaluation of the respective hop oils. Sulphur-containing compounds were revealed by capillary gas chromatography using sulphur-selective atomic emission detection. Complete separation and quantification of all hop α;-acids and β;-acids was effected by microemulsion electrokinetic chromatography coupled to diode array detection .     

Mechanism of gushing induction by carbon dioxide transfer activator

The article deals with the activation of carbon dioxide transfer from carbonated beverages. As a model compounds agents produced by Trichoderma reesei and harzianum and degraded hop iso‐extract were selected. These substances were added to the carbonated water or beer and their effect was compared. The method of pressure growth in the bottle headspace after rapid piercing and re‐closing the bottle was used. Some carbon dioxide transfer activators accelerated CO₂ escape even at rest; others required shaking for different periods. The pressure growth measurement allowed the prediction of gushing before its occurrence. Copyright © 2017 The Institute of Brewing & Distilling     

Modification of perceived beer bitterness intensity,character and temporal profile by hop aroma extract

The effect of hop aroma on perceived bitterness intensity, character and temporal profile of beer was investigated. A hop aroma extract was added at 3 levels (0, 245, 490 mg/L) to beers at low, medium and high bitterness. Beers were evaluated for perceived bitterness intensity, harshness, roundedness and linger by a trained panel using a rank-rating technique at each bitterness level, with and without nose clips. The use of nose clips enabled the olfactory aspect to be decoupled from taste and mouthfeel aspects of bitterness perception. Results showed significant modification of perceived bitterness in beer by hop aroma depending on the inherent level of bitterness. These modifications were mainly driven by olfaction – in an example of taste-aroma interactions, as well as certain tactile sensations elicited by the hop aroma extract in the oral cavity. At low bitterness, beers with hop aroma added were perceived as more bitter, and of ‘rounded’ bitterness character relative to those without hop aroma. When judges used nose clips, this effect was completely eliminated but the sample was perceived to have a ‘harsh’ bitterness character. Conversely, at high bitterness, even when nose clips were used, judges still perceived beers containing hop aroma to be more bitter. These increases in bitterness perception with nose clips indicates the stimulating of other receptors, e.g. trigeminal receptors by hop aroma extract, which in tandem with the high bitterness, cause perceptual interactions enhancing bitterness intensity and also affecting bitterness character. Bitterness character attributes such as ‘round’ and ‘harsh’ were found to significantly depend on bitterness and aroma levels, with the second level of aroma addition (245 mg/L) giving a ‘rounded’ bitterness in low bitterness beers but ‘harsh’ bitterness in high bitterness beers. The impact of aroma on temporal bitterness was also confirmed with time-intensity measurements, and found to be mostly significant at the highest level of hop aroma addition (490 mg/L) in low bitterness beers. These findings represent a significant step forward in terms of understanding bitterness flavour perception and the wider impact of hop compounds on sensory perception.     

FLAVOUR AND HAZE STABILITY DIFFERENCES DUE TO HOP TANNINS IN ALL-MALT PILSNER BEERS BREWED WITH PROANTHOCYANIDIN-FREE MALT

All-malt Pilsner beers were brewed with proanthocyanidin-free malt (ant 13 × 13 × Rupal). Hopping was with n-hexane tannin-free hop extract with or without n-hexane extracted hop residue or with whole leaf hops. The different beers were analysed chemically and presented to an expert panel to detect possible preferences and differences in bitterness and astringency. The impact of hop proantho-cyanidins on haze formation is comparable to that of malt proanthocyanidins. No differences between the beers were found in triangular tests. Statistical analysis of the paired comparison tests showed that hop proanthocyanidins do not contribute to the bitterness of beer since beer brewed with tannin-free hop extract is slightly more bitter than beer brewed with whole leaf hops. No differences in astringency were noted between beers brewed with or without hop proanthocyanidins and it was found that the panel expressed a very slight preference for beer brewed with n-hexane hop extract over beer brewed with both n-hexane hop extract and extracted hop residue.     

PREPARATION OF HOP EXTRACTS RICH IN PARTICULAR CONSTITUENTS*

When a column containing powdered hops is extracted with liquid carbon dioxide, chromatographic separation of hop components occurs. They are extracted in the order essential oils, β-acids, α-acids; and the separation is enhanced when finely milled hops are extracted. Early fractions (～0·5 hour) contain a high proportion of the available essential oils when hops are extracted at ?20°C and such extracts are suitable as a replacement for dry hops. Fractions can be obtained from extractions at ～7°C which are rich in α-acids and contain low levels of β-acids. Small amounts of fats and waxes are normally present in fractions collected towards the end of a run when seeded hops are extracted.     

HOP SUBSTANCES AND YEAST BEHAVIOUR

Top fermentation yeast strains vary in their ability to form a yeast head in the absence of hop substances. However, the addition of isohumulone or humulone to unhopped wort stimulates yeast-head formation. A quantitative method for the estimation of hop substances bound to the yeast cell is described and is used to demonstrate that in top fermentation, most of the adsorbed bitter substances are present in the head. It is shown that most of the hop substances in the yeast head are transported there by bubbles of carbon dioxide; in bottom fermentation, considerable quantities are present in the surface foam. In comparison with hopped wort the fermentation of unhopped wort with Saccharomyces cerevisiae (N.C.Y.C. 240) is characterized by an increased amount of yeast in suspension during fermentation, although there is no increase in the rate of attenuation.     

CONTROLLING MALTING LOSSES WITH ANOXIA,CARBON DIOXIDE,AND SULPHUR DIOXIDE

Micromalting trials were used to evaluate the effectiveness of various treatments with anaeroblosis, carbon dioxide or sulphur dioxide in controlling malting losses with grain treated with gibberellic acid. Periods of increasing anoxia, with carbon dioxide accumulation as in Kropff malting, produced malt with a reduced malting loss and a lower hot water extract than control malting. Covering germinating barley with atmospheres containing various partial pressures of carbon dioxide reduced malting losses, but the resulting malts were usually inferior in quality to the controls. Sulphur dioxide gas, applied to moist germinating barley three days after casting, reduced malting losses by almost 3%, and increased the hot water extract by about 3 lb./Qr. relative to control malts. The treated malt occupied less space than the control, and the heat output was reduced. Sulphur dioxide treatment and only 4 days' germination produced a malt in high yield, with an extract identical to that of a control malt germinated for five days. The sulphur dioxide malts yielded worts with lower pH and higher soluble nitrogen values than the control and the fermentability of the worts was normal.     

中压法回收生产高纯度食品级液体二氧化碳的研究

分析了酒精厂二氧化碳形成机理，比较各种二氧化碳生产方法的优缺点。重点介绍中压法回收生产高纯度食品级液体二氧化碳的生产方法及压缩、净化、液化和灌装技术。     

MODELING of TRIGLYCERIDE DISTRIBUTION and YIELD of ANHYDROUS MILK FAT IN A CONTINUOUS SUPERCRITICAL CARBON DIOXIDE EXTRACTION SYSTEM

A mathematical model was developed for continuous extraction of multicomponent mixture anhydrous milk fat (AMF) with supercritical carbon dioxide (SC-CO₂) as its solvent. At a constant temperature and pressure, the triglyceride mixture was separated into vapor and liquid fractions. the composition distribution (indicated by acyl carbon number), mass distribution and yield of AMF were calculated by the model based on thermodynamic equilibrium and material balance. the feed composition and distribution coefficient were required information in this model. the experimental values for the extract were in good agreement with the model used. the results for the raffinate were not as precisely modeled. the main factors which affected the model were temperature, pressure, solvent/feed ratio and extract fraction.     

胡萝卜素的提取及其护肝作用的研究

研究超临界CO2萃取胡萝卜素及其对四氯化碳化学性肝损伤的保护作用。结果表明:超临界CO2萃取的胡萝卜素能显著降低四氯化碳致小鼠急性肝损伤血清ALT、AST升高,减轻四氯化碳对肝脏细胞的病理损伤。