Vitality enhancement of the rehydrated active dry wine yeast

In winemaking, spontaneous grape must fermentations have been replaced by inoculation of commercial active dry wine yeast (ADWY). Yeast rehydration is the key to avoiding stuck and sluggish fermentations. Despite the importance of this step, not enough is known about what this process implies for winemaking as a whole or about what kind of practices could help to improve it. The main aim of this study is to determine the best yeast rehydration conditions for ensuring good cell viability and vitality before inoculation into the must. The experimental rehydration media in this study can be divided into four groups: carbon and nitrogen compounds, metallic ions, oxidant and antioxidant agents, and membrane fluidity agents. We studied the biochemical and biophysical behaviour of ADWY after rehydration in the various media under oenological conditions, i.e. incubation at 37 degrees C for 30 min. The viability of rehydrated yeast cells was evaluated by plating, and assessed by fluorescence microscopy and flow cytometry. The vitality of rehydrated cells was estimated by indirect impedance. The rehydrating solution complemented with magnesium provided the best vitality rate because the time taken to reach the activity threshold was cut by two thirds. This improvement was also illustrated by the less time needed to stop the leakage of intracellular compounds during the rehydration process.     

Effect of the respiro-fermentative balance during yeast propagation on fermentation and wort attenuation

Breweries use different yeast strains to create beers with different flavours and aromas. Yeast propagation must produce yeast that performs consistently from the first fermentation to harvesting and re-pitching in subsequent fermentations. Breweries propagate yeast in wort leading to low efficiency fermentative growth in Crabtree-positive yeast. There is limited knowledge on the impact on beer production when fermenting with yeast propagated in sugar limited and nutrient supplemented wort. It was hypothesised that propagating yeast in this way would have a positive impact on subsequent fermentation performance. Saccharomyces cerevisiae was propagated at the laboratory scale in standard wort with a high carbon to nitrogen (C:N) ratio (850) or in modified wort supplemented with yeast extract to achieve a low C:N ratio (100) and at varying sugar concentrations. Propagation in low C:N wort with 2°P sugar yielded a 27% decrease in fermentation efficiency and a 46% increase in cell production compared to 2°P high C:N wort. This suggests nitrogen is critical to the respiro-fermentative balance during growth. Yeast propagated in standard wort resulted in slower fermentations and significant under-attenuation compared to yeast grown in the modified wort with low sugar and high nitrogen. The results of this study suggest the nitrogen and sugar content drive the respiro-fermentative balance during yeast propagation. The metabolism of yeast during propagation induces significant downstream impacts on the subsequent fermentation performance and wort attenuation. © 2020 The Institute of Brewing & Distilling     

Impact of the CaCl2 content in the rehydration media on the microcapsule formation out of spray dried capsule precursors for the immobilization of probiotic bacteria

The aim of this work was to develop a capsule formation process at moderate temperatures with a high encapsulation yield (EY) of probiotic bacteria. Capsule precursors (CP) obtained by spray drying were rehydrated at 40 °C in aqueous solution to form water-insoluble hydrogel capsules. The CaCl₂ concentration (0–2 mm) in the rehydration solution was varied. The rehydration step was evaluated regarding matrix stability and capsule size. The results show that only low amounts of non-aggregated casein remain in the rehydration media at or above 1.3 mm CaCl₂. Additionally, under this condition the particle size distribution shows no particles with the size of non-aggregated caseins and bacteria. Both results indicate a completely, stable matrix structure. To gain a deeper understanding the EY and capsule morphology by scanning electron microscope (SEM) images were assessed. The SEM images show that the bacterial cells are fully embedded in a dense casein network structure. The determined EY was ∼85%.     

Comparing the Impact of Environmental Factors During Very High Gravity Brewing Fermentations

The impact of the initial dissolved oxygen, fermentation temperature, wort concentration and yeast pitching rate on the major fermentation process responses were evaluated by full factorial design and statistical analysis by JMP 5.01 (SAS software) software. Fermentation trials were carried out in 2L‐EBC tall tubes using an industrial lager brewing yeast strain. The yeast viability, ethanol production, apparent extract and real degree of fermentation were monitored. The results obtained demonstrate that very high gravity worts at 22°P can be fermented in the same period of time as a 15°P wort, by raising the temperature to 18°C, the oxygen level to about 22 ppm, and increasing the pitching rate to 22 × 10⁶ cell/mL. When diluting to obtain an 11.5°P beer extract, the volumetric brewing capacity increased 91% for the 22°P wort fermentation and 30% using the 15°P wort. After dilution, the fermentation of the 22°P wort resulted in a beer with higher esters levels, primarily the compound ethyl acetate.     

Effect of additives on the rehydration of Saccharomyces cerevisiae wine strains in active dry form: influence on viability and performance in the early fermentation phase

The effect of five additives on the rehydration process of three commercial Saccharomyces cerevisiae wine strains, in the form of active dry yeast, was tested using the approach of design of experiments. The response to additives was monitored by observing the viability, measured using fluorescence methodology at the end of the rehydration experiments, and fermentative performance, focusing attention on the first phase of fermentation, assessed based on ethanol production and the total number of cells after 48 h from the time of inoculation in synthetic must. The results showed a correlation between viability and the presence of magnesium in the rehydration medium. However, improvement in viability was not associated with better fermentation performance, which was not affected or in some cases significantly reduced. Among the additives examined, only rehydration with inactive dry yeast and ammonium showed a positive effect on the subsequent fermentations, but not for all of the strains tested. In general, considering all of the additives tested, no relationship was found between viability at the end of rehydration and fermentation performance. These findings suggest that the viability of the rehydrated yeast cells may not be a good index of fitness in the subsequent fermentation. Copyright © 2014 The Institute of Brewing & Distilling     

Kinetics of water absorption and soluble‐solid loss of hot‐air‐dried carrots during rehydration

Cubes of carrots dried at 60, 70, 80 and 90 °C were rehydrated at 20 and 95 °C. Kinetics of water gain and soluble‐solid loss were monitored and described by Peleg model. Dry matter holding capacity, water absorption capacity and rehydration ability were derived to assess the rehydration process. It was found that leaching flow was higher for the samples dried at higher temperatures. Rehydration ability and dry matter holding capacity of the samples rehydrated at 95 °C were higher than those observed for the samples soaked at 20 °C. Swelling of carrots during rehydration neither depended on temperature of drying nor on the temperature of the water. The results indicate that the use of low drying temperatures is suitable for preserving the quality attributes of carrots after rehydration.     

Optimisation of osmotic dehydration of carrot cubes in sucrose-salt solutions using response surface methodology

Osmotic dehydration of carrot cubes in ternary solution of water, sucrose and sodium chloride at different solution concentrations, temperatures and process durations were analysed for water loss and solute gain during osmotic dehydration. The osmotically pre-treated carrot cubes were further dehydrated in a cabinet dryer at 65 °C and were then rehydrated in water at ambient temperature of water for 10–12 h and were analysed for rehydration ratio, shrinkage and overall acceptability after rehydration. The process was optimised for maximum water loss, rehydration ratio and overall acceptability of the rehydrated product, and for minimum solute gain and shrinkage of rehydrated product by response surface methodology. The optimum conditions of various process parameters are 50°B+10% w/v aqueous sodium chloride concentration, 46.5 °C solution temperature and 180 min process duration.     

Influence of Drying Temperature and Rehydration on Selected Textural Properties of Carrots

Cubes of carrots dried at 60, 70, 80, and 90°C were rehydrated up to 180 min at 20°C and up to 10 min at 95°C. Kinetics of cutting strength were determined for the samples soaked at 95°C. Compression stress relaxation behavior of the samples was studied on carrots rehydrated at 20 and 95°C. Kinetics of cutting strength were satisfactorily described by means of a first-order kinetic model. The compression stress relaxation of carrots was analyzed using five element Maxwell and empirical Peleg models. Both of the models were found to be appropriate for characterizing viscoelastic properties of dried and rehydrated carrot cubes. The results indicated that the use of low drying temperatures was suitable for preserving the quality attributes of carrots after rehydration, and drying air temperature of 60°C was chosen as the most appropriate for hot air processing of carrots.     

Rehydration of Freeze‐Dried and Convective Dried Boletus edulis Mushrooms: Effect on Some Quality Parameters

ABSTRACT: Quality of rehydrated products is a key aspect linked to rehydration conditions. To assess the effect of rehydration temperature on some quality parameters, experiments at 20 and 70 °C were performed with convective dried and freeze‐dried Boletus edulis mushrooms. Rehydration characteristics (through Peleg's parameter, k₁, and equilibrium moisture, W_e), texture (Kramer), and microstructure (Cryo‐Scanning Electron Microscopy) were evaluated. Freeze‐dried samples absorbed water more quickly and attained higher W_e values than convective dried ones. Convective dehydrated samples rehydrated at 20 °C showed significantly lower textural values (11.9 ± 3.3 N/g) than those rehydrated at 70 °C (15.7 ± 1.2 N/g). For the freeze‐dried Boletus edulis, the textural values also exhibited significant differences, being 8.2 ± 1.3 and 10.5 ± 2.3 N/g for 20 and 70 °C, respectively. Freeze‐dried samples showed a porous structure that allows rehydration to take place mainly at the extracellular level. This explains the fact that, regardless of temperature, freeze‐dried mushrooms absorbed water more quickly and reached higher W_e values than convective dried ones. Whatever the dehydration technique used, rehydration at 70 °C produced a structural damage that hindered water absorption; consequently lower W_e values and higher textural values were attained than when rehydrating at 20 °C.     

High gravity primary continuous beer fermentation using flocculent yeast biomass

The current work assessed a new immobilized cell reactor system throughout a long‐term (54 days) continuous primary fermentation of lager‐type wort of high specific gravity. The experiment was performed in a 4 L airlift bioreactor and immobilization of biomass was attained solely by flocculation. Despite the constant liquid agitation and washout of biomass, up to 53 g dry wt/L of yeast remained immobilized in the system. Two types of beer were produced without interrupting the reactor, based on two types of wort: a Pilsener type with high specific gravity of 15.6 ± 0.3°P; and a dark lager wort with specific gravity of 14.4 ± 0.03°P. Even during the inlet of high gravity wort, the desired attenuation was achieved without the need for either recirculation or an auxiliary second stage bioreactor. The specific saccharide consumption rate was kept around 7.9 ± 0.4 g/L/h and ethanol productivity oscillated at 3.36 ± 0.2 g/L/h for nearly a month. During this period the volumetric productivity of the current bioreactor reached 1.6 L beer/L/day. The green beers produced from the Pilsener and dark lager worts met the standards of regular finished primary beer fermentation. The productivity of diacetyl through the entire experiment could be correlated to the free amino nitrogen consumption rate. Copyright © 2014 The Institute of Brewing & Distilling     

Low Temperature Blanching Affects Firmness and Rehydration of Dried Cauliflower Florets

Cauliflower florets were blanched at 55, 60, 65, and 70°C, held without cooling for 15, 30, 45, 60, and 90 min, blanched again at 100°and then dried in a hot air dehydrater. The coefficient for the rate of rehydration (?) was calculated using a diffusion model. Rehydrated samples were divided into two equal parts, one part was boiled in water and the other was uncooked. Firmness of rehydrated samples was measured by back extrusion. Blanching cauliflower between 55°and 70°before dehydration caused a substantial increase in extrusion forces after rehydration. Cooking the rehydrated cauliflower decreased firmness of all samples. However, the degree of softening caused by cooking was proportionally less for the low temperature blanch treatments than for the controls.     

Improvement of the slide culture technique for the assessment of yeast viability

This work aimed to improve the slide culture technique (SCT) for the assessment of yeast viability. Thus, all the steps of the SCT were standardized: a sample of 20 μL containing 1 × 10⁵ cells/mL was placed in a ~ 20 × 20 mm YPD agar block and incubated for 16–24 h, at 25°C. It was proposed the use of calcofluor white (CFW) to facilitate the microscopic observation of yeast cells. The viability of cell populations in different physiological states (healthy, ethanol stressed and starved cells), assessed by SCT (without or with CFW), did not differ significantly (p  < 0.01). In addition, the viability of healthy and ethanol stressed cells determined by the SCT and the standard plate count technique (PCT) did not differ significantly (p  < 0.01). In conclusion, the improved SCT is a fast and reliable alternative to PCT for the evaluation of yeast viability in research and in the industry. Copyright © 2017 The Institute of Brewing & Distilling     

Rehydration of air-dried Shiitake mushroom (Lentinus edodes) caps: Comparison of conventional and vacuum water immersion processes

Air-dried Shiitake mushroom (Lentinus edodes) caps were rehydrated using conventional and vacuum techniques, at different temperatures (30, 40, 50 and 80 °C) and times (1, 2, 3, 6, 9, 12, 15, 18, 21, 120, 150 and 210 min). Three empirical models were used to model the rehydration process: 1st order kinetics, Peleg’s model and the Weibull distribution function. To determine the effects of temperature and pressure on the mushroom caps, the texture of the rehydrated material was determined, evaluating peak shear force and microstructure using cold-stage scanning electron microscopy (cryo-SEM). The rehydration of the mushrooms was found to be temperature and pressure-dependant. The speed of vacuum rehydration was faster compared to conventional rehydration. When rehydrated at 80 °C, a loss in rehydration capacity was observed in both cases, which can be explained by the structural damage and cell shrinkage which occurred during air-drying. Also, the vacuum rehydrated samples had the lowest toughness values. It was concluded that vacuum rehydration of dried Shiitake mushroom caps could be a feasible alternative to the conventional rehydration process, resulting in a lower immersion time and in a desirable texture.     

Effect of growth temperature on yeast lipid composition and alcoholic fermentation at low temperature

The loss of viability of wine yeast strains due to low-temperature fermentations could be overcome by increasing their stress tolerance and adaptability. Changes in membrane lipid composition are one of the first responses to cold stress. The aim of this study was to analyze the various adaptation mechanisms to low temperatures by comparing the better adapted Saccharomyces species. The viability, vitality, fermentation capacity, and lipid composition of different Saccharomyces species (S. cerevisiae, S. bayanus, S. uvarum, and a hybrid S. cerevisiae/S. uvarum) with different fermentative origins (wine, beer, and baker’s strains together with a laboratory strain) were compared after culturing at low (13 °C) and optimal (25 °C) temperatures. In spite of specific responses of the different strains/species, the results showed that at low temperature, the medium-chain fatty acid and the triacylglyceride content increased, whereas the phosphatidic acid content and the phosphatidylcholine/phosphatidylethanolamine ratio decreased. Only the laboratory strain was not able to ferment the sugars, and after growing at both temperatures, its lipid composition was very different from that of the other strains. The hybrid strain showed the highest sugar consumption at 13 °C and the best vitality whatever the preculture temperature used. The rest of the species needed a preadaptation at low temperature involving a change in their lipid composition to improve their fermentation rate at 13 °C.     

Effect of puffing conditions on physical properties and rehydration characteristic of instant rice product

The aim of this work was to study the effects of puffing conditions on the properties of instant rice and to obtain optimal processing condition for product with rehydration time within 5 min. Thai jasmine rice was soaked, cooked and dried at 80 °C in a tray dryer before being puffed at different moisture contents (15–20% wb), temperatures (200–220 °C) and time intervals (20–30 s). The rice puffed at higher moisture contents and puffing temperatures for longer time exhibited higher volume expansion ratios and shorter rehydration times. Presumably, case hardening of the grain surface occurred. Instant rice that can be rehydrated in 5 min with more acceptable hardness than the commercial instant rice was obtained. Regression models to predict the quality of instant rice were developed using response surface methodology.     

The effect of blanching on the quality of dehydrated broccoli florets

Different blanching treatments were applied to broccoli florets prior to dehydration in order to improve product quality. The pretreatments used were a conventional blanching in water at 99ǃ °C, and a stepwise blanching (a blanching at low temperature followed by a short blanching at high temperature after a holding time) using different temperatures for the first step (50, 55, 60, 65 and 70 °C). Five rehydration temperatures were used (25, 40, 55, 65 and 80 °C). Rehydration rate (D_eff and W_e), chlorophyll content and texture of the rehydrated product were evaluated. Rehydration was modelled according to Fick's diffusion equation. A good agreement between the model and the experimental data was obtained when D_eff and W_e values were identified for each temperature (average explained variance 96.9%). Samples stepwise blanched at 60 °C showed, on the average, the lowest W_e values. Stepwise blanching at 60-65 °C and rehydration at 25-55 °C were the combinations that gave the firmest product. Stepwise blanching at 50 °C together with the conventional blanching (99ǃ °C) and rehydration between 25 and 65 °C were the combinations that allowed preservation of the highest chlorophyll content. From these results, it seems difficult to obtain firm samples with a high chlorophyll content without additives.     

Evaluation of the fermentative potential of Candida zemplinina yeasts for craft beer fermentation

The fermentative potential of Candida zemplinina Y.01667 and Y.01670 was evaluated to explore the potential use of these yeasts for craft beer fermentations. Fermentation experiments were carried out at different temperatures and soluble solid concentrations, using synthetic media with glucose syrup as a sugar source and with a laboratory malt wort plus different adjuncts. Results showed that both strains fermented well at 14 °C and had improved fermentative activity at 20 °C. The fermentative kinetics of C. zemplinina Y.01667 and Y.01670 were not affected when experiments at higher concentrations of soluble solids were conducted. Furthermore, C. zemplinina strains had better growth, higher viable cells counts, less free amino nitrogen consumption, lower sedimentation rates and slighter changes in pH values, when compared with results of the lager beer yeast Saccharomyces cerevisiae S‐23 in the synthetic medium tested. Fermentations in a malt wort with different adjuncts indicated that C. zemplinina Y.01670 could possibly be used as a yeast in craft beer production. Copyright © 2016 The Institute of Brewing & Distilling     

Rehydration Capacity of Chilean Papaya (Vasconcellea pubescens): Effect of Process Temperature on Kinetic Parameters and Functional Properties

Slabs of Chilean papaya hot air-dried at 60 °C were rehydrated at 20, 40, 60, and 80 °C to study the influence of process temperature on mass transfer kinetics during rehydration. Diffusive and empirical models were selected to simulate the experimental rehydration curves. All models parameters showed dependence with temperature, thus activation energy could be estimated according to an Arrhenius-type equation. Among the applied models, Weibull provided the best fit for each rehydration curve based on the statistical tests RMSE, SSE, and chi-square. According to these results, this model could be used to estimate the rehydration time of Chilean papaya. In addition, rehydration ratio and water-holding capacity were analyzed. Both indices showed a decrease with increasing rehydration temperature indicating modification of the papaya cell structure due to thermal treatment which resulted in a reduction of the rehydration ability, in particular at high rehydration temperatures.     

BREAKAGE SUSCEPTIBILITY of SHELLED CORN DUE to REHYDRATION and REDRYING

Processing activities such as drying expose grains to temperature and moisture gradients resulting to increased susceptibility of corn breakage. the effect of rehydration and redrying rates on the breakage susceptibility of corn was compared and evaluated. Dried corn samples were rehydrated and redried artificially. Breakage susceptibility of the samples were tested using a food grinder (blender) and Instron testing machine. Treatments consisting of a cycle of rehydration and redrying represented different rates of moisture sorption. Initial sample moisture, rehydration methods and redrying temperatures were used in comparing breakage susceptibility. Samples of low initial moisture had higher breakage susceptibility as compared to higher initial moisture samples. the rehydration method representing the highest moisture adsorption rate resulted to samples which were more susceptible to breakage than the two rehydration methods representing intermediate and slow rates of moisture adsorption. Temperature of redrying also showed significant effects with high temperatures (80°C) resulting to grains with higher breakage susceptibility compared to samples redried with unheated air (30°C). Breakage susceptibility increased when samples were rehydrated and increased much more when they were redried.     

PITCHING RATE IN HIGH GRAVITY BREWING

The optimal pitching rate in high gravity worts (12–16°P) was about 0.3 g/l wet weight (2.3 × 10⁶ counted cells/ml) and per one percent of original wort gravity. In very high gravity worts (20–23°P) the corresponding figure was 0.4 g/l (2.9 × 10⁶ cells/ml). Higher amounts of yeast did not improve the fermentation rate. With increased original wort gravity, flocculation of the yeast weakened and the amount of cropped yeast decreased. The viability of the crop yeast was good. In the conditions used, excessive production of acetate esters occurred only with pitching rates lower than the recommended rate. As the original wort gravity increased, more fermentable extract was metabolized to ethanol rather than utilized for yeast growth. The highest ethanol yield obtained was 10.9% (v/v).